WEBVTT Kind: captions Language: en 00:00:01.160 --> 00:00:06.690 align:start position:0% [Music] 00:00:06.690 --> 00:00:06.700 align:start position:0% 00:00:06.700 --> 00:00:10.430 align:start position:0% [Music] 00:00:10.430 --> 00:00:10.440 align:start position:0% [Music] 00:00:10.440 --> 00:00:12.549 align:start position:0% [Music] hello<00:00:11.120> everyone<00:00:11.480> who<00:00:11.639> could<00:00:11.840> wake<00:00:12.080> up<00:00:12.400> thank 00:00:12.549 --> 00:00:12.559 align:start position:0% hello everyone who could wake up thank 00:00:12.559 --> 00:00:14.070 align:start position:0% hello everyone who could wake up thank you<00:00:12.639> for 00:00:14.070 --> 00:00:14.080 align:start position:0% you for 00:00:14.080 --> 00:00:17.510 align:start position:0% you for coming<00:00:15.080> uh<00:00:15.280> this<00:00:15.480> talk<00:00:15.759> is<00:00:16.039> about<00:00:16.359> EF<00:00:17.279> uh<00:00:17.359> we 00:00:17.510 --> 00:00:17.520 align:start position:0% coming uh this talk is about EF uh we 00:00:17.520 --> 00:00:19.790 align:start position:0% coming uh this talk is about EF uh we had<00:00:17.640> a<00:00:17.760> very<00:00:17.960> nice<00:00:18.160> introduction<00:00:18.720> thanks<00:00:19.039> Alex 00:00:19.790 --> 00:00:19.800 align:start position:0% had a very nice introduction thanks Alex 00:00:19.800 --> 00:00:21.590 align:start position:0% had a very nice introduction thanks Alex uh<00:00:19.920> in<00:00:20.039> the<00:00:20.160> previous<00:00:20.519> presentation<00:00:21.080> so 00:00:21.590 --> 00:00:21.600 align:start position:0% uh in the previous presentation so 00:00:21.600 --> 00:00:23.189 align:start position:0% uh in the previous presentation so hopefully<00:00:22.080> you<00:00:22.199> know<00:00:22.439> by<00:00:22.600> now<00:00:22.840> this<00:00:22.920> is<00:00:23.039> a 00:00:23.189 --> 00:00:23.199 align:start position:0% hopefully you know by now this is a 00:00:23.199 --> 00:00:24.230 align:start position:0% hopefully you know by now this is a series<00:00:23.480> of 00:00:24.230 --> 00:00:24.240 align:start position:0% series of 00:00:24.240 --> 00:00:26.750 align:start position:0% series of proposals<00:00:25.240> that<00:00:25.400> aims<00:00:25.720> at<00:00:25.880> redesigning<00:00:26.560> and 00:00:26.750 --> 00:00:26.760 align:start position:0% proposals that aims at redesigning and 00:00:26.760 --> 00:00:30.509 align:start position:0% proposals that aims at redesigning and improving<00:00:27.359> evm<00:00:27.920> in<00:00:28.160> various<00:00:28.640> ways<00:00:29.320> and<00:00:29.800> uh<00:00:30.439> I 00:00:30.509 --> 00:00:30.519 align:start position:0% improving evm in various ways and uh I 00:00:30.519 --> 00:00:32.870 align:start position:0% improving evm in various ways and uh I will<00:00:30.720> be<00:00:30.880> talking<00:00:31.240> about<00:00:31.599> one<00:00:31.920> part<00:00:32.160> of<00:00:32.320> it<00:00:32.599> one 00:00:32.870 --> 00:00:32.880 align:start position:0% will be talking about one part of it one 00:00:32.880 --> 00:00:35.069 align:start position:0% will be talking about one part of it one EIP<00:00:33.239> 5450<00:00:33.879> St 00:00:35.069 --> 00:00:35.079 align:start position:0% EIP 5450 St 00:00:35.079 --> 00:00:37.389 align:start position:0% EIP 5450 St validation<00:00:36.079> stack<00:00:36.399> validation<00:00:36.960> is<00:00:37.200> in 00:00:37.389 --> 00:00:37.399 align:start position:0% validation stack validation is in 00:00:37.399 --> 00:00:39.869 align:start position:0% validation stack validation is in general<00:00:38.120> one<00:00:38.480> part<00:00:38.680> of<00:00:38.800> a<00:00:39.000> bigger<00:00:39.600> code 00:00:39.869 --> 00:00:39.879 align:start position:0% general one part of a bigger code 00:00:39.879 --> 00:00:42.110 align:start position:0% general one part of a bigger code validation<00:00:40.559> procedure<00:00:41.120> that<00:00:41.320> happens<00:00:41.760> before 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00:00:50.879 align:start position:0% of it is uh to get rid of repeated 00:00:50.879 --> 00:00:53.590 align:start position:0% of it is uh to get rid of repeated checks<00:00:51.480> during<00:00:51.879> executing<00:00:52.359> the<00:00:52.520> same<00:00:52.760> code 00:00:53.590 --> 00:00:53.600 align:start position:0% checks during executing the same code 00:00:53.600 --> 00:00:56.029 align:start position:0% checks during executing the same code and<00:00:53.760> instead<00:00:54.320> if<00:00:54.559> we<00:00:54.719> can<00:00:54.879> if<00:00:55.039> we<00:00:55.199> can<00:00:55.640> do<00:00:55.879> the 00:00:56.029 --> 00:00:56.039 align:start position:0% and instead if we can if we can do the 00:00:56.039 --> 00:00:58.189 align:start position:0% and instead if we can if we can do the check<00:00:56.320> once<00:00:56.760> before<00:00:57.039> code<00:00:57.280> is<00:00:57.399> being<00:00:57.600> deployed 00:00:58.189 --> 00:00:58.199 align:start position:0% check once before code is being deployed 00:00:58.199 --> 00:01:01.110 align:start position:0% check once before code is being deployed then<00:00:58.399> we<00:00:58.719> do<00:00:59.039> that<00:00:59.440> and<00:01:00.039> then<00:01:00.359> assume<00:01:00.840> it<00:01:00.960> is 00:01:01.110 --> 00:01:01.120 align:start position:0% then we do that and then assume it is 00:01:01.120 --> 00:01:04.990 align:start position:0% then we do that and then assume it is satisfied<00:01:02.039> during<00:01:03.039> uh<00:01:03.480> execution<00:01:04.239> and 00:01:04.990 --> 00:01:05.000 align:start position:0% satisfied during uh execution and 00:01:05.000 --> 00:01:07.590 align:start position:0% satisfied during uh execution and then<00:01:06.000> basically<00:01:06.439> we<00:01:06.560> can<00:01:06.840> Adit<00:01:07.240> the<00:01:07.400> same 00:01:07.590 --> 00:01:07.600 align:start position:0% then basically we can Adit the same 00:01:07.600 --> 00:01:10.590 align:start position:0% then basically we can Adit the same checks<00:01:08.320> uh<00:01:08.680> uh<00:01:08.799> at<00:01:09.119> runtime<00:01:10.119> for<00:01:10.360> stack 00:01:10.590 --> 00:01:10.600 align:start position:0% checks uh uh at runtime for stack 00:01:10.600 --> 00:01:13.469 align:start position:0% checks uh uh at runtime for stack validation<00:01:11.040> in<00:01:11.240> particular<00:01:12.159> this<00:01:12.799> means 00:01:13.469 --> 00:01:13.479 align:start position:0% validation in particular this means 00:01:13.479 --> 00:01:15.270 align:start position:0% validation in particular this means ensuring<00:01:14.040> stack<00:01:14.360> correctness<00:01:14.880> of<00:01:15.040> every 00:01:15.270 --> 00:01:15.280 align:start position:0% ensuring stack correctness of every 00:01:15.280 --> 00:01:18.550 align:start position:0% ensuring stack correctness of every instruction<00:01:15.759> in<00:01:15.960> the<00:01:16.119> code<00:01:16.640> and<00:01:17.040> in<00:01:17.280> evm<00:01:18.200> as<00:01:18.400> we 00:01:18.550 --> 00:01:18.560 align:start position:0% instruction in the code and in evm as we 00:01:18.560 --> 00:01:20.950 align:start position:0% instruction in the code and in evm as we don't<00:01:18.880> have<00:01:19.520> uh<00:01:19.840> types<00:01:20.119> of<00:01:20.280> the<00:01:20.439> values<00:01:20.720> on 00:01:20.950 --> 00:01:20.960 align:start position:0% don't have uh types of the values on 00:01:20.960 --> 00:01:23.749 align:start position:0% don't have uh types of the values on stack<00:01:21.759> this<00:01:22.000> simply<00:01:22.320> means<00:01:22.840> making<00:01:23.159> sure<00:01:23.520> that 00:01:23.749 --> 00:01:23.759 align:start position:0% stack this simply means making sure that 00:01:23.759 --> 00:01:25.749 align:start position:0% stack this simply means making sure that none<00:01:24.040> of<00:01:24.159> the<00:01:24.320> instructions<00:01:25.040> overflow<00:01:25.600> or 00:01:25.749 --> 00:01:25.759 align:start position:0% none of the instructions overflow or 00:01:25.759 --> 00:01:27.789 align:start position:0% none of the instructions overflow or underflow<00:01:26.479> the 00:01:27.789 --> 00:01:27.799 align:start position:0% underflow the 00:01:27.799 --> 00:01:30.550 align:start position:0% underflow the stack<00:01:28.799> and<00:01:29.000> given<00:01:29.280> that<00:01:29.479> we<00:01:29.560> check<00:01:29.759> this<00:01:30.040> once 00:01:30.550 --> 00:01:30.560 align:start position:0% stack and given that we check this once 00:01:30.560 --> 00:01:32.310 align:start position:0% stack and given that we check this once uh<00:01:30.680> at<00:01:30.840> validation<00:01:31.360> then<00:01:31.520> we<00:01:31.640> can<00:01:31.840> omit<00:01:32.159> these 00:01:32.310 --> 00:01:32.320 align:start position:0% uh at validation then we can omit these 00:01:32.320 --> 00:01:35.389 align:start position:0% uh at validation then we can omit these checks<00:01:32.759> from<00:01:33.079> The<00:01:33.439> Interpreter<00:01:33.960> Loop<00:01:34.920> and<00:01:35.159> one 00:01:35.389 --> 00:01:35.399 align:start position:0% checks from The Interpreter Loop and one 00:01:35.399 --> 00:01:37.310 align:start position:0% checks from The Interpreter Loop and one important<00:01:35.840> consideration<00:01:36.479> to<00:01:36.720> keep<00:01:36.880> in<00:01:37.079> mind 00:01:37.310 --> 00:01:37.320 align:start position:0% important consideration to keep in mind 00:01:37.320 --> 00:01:40.109 align:start position:0% important consideration to keep in mind when<00:01:37.520> designing<00:01:38.000> St<00:01:38.240> validation<00:01:38.880> is<00:01:39.799> keeping 00:01:40.109 --> 00:01:40.119 align:start position:0% when designing St validation is keeping 00:01:40.119 --> 00:01:42.190 align:start position:0% when designing St validation is keeping its<00:01:40.360> complexity<00:01:40.960> linear<00:01:41.439> in<00:01:41.560> the<00:01:41.680> size<00:01:41.880> of<00:01:42.040> the 00:01:42.190 --> 00:01:42.200 align:start position:0% its complexity linear in the size of the 00:01:42.200 --> 00:01:45.910 align:start position:0% its complexity linear in the size of the code<00:01:43.159> uh<00:01:43.640> this<00:01:44.040> is<00:01:45.000> important<00:01:45.520> because<00:01:45.759> we 00:01:45.910 --> 00:01:45.920 align:start position:0% code uh this is important because we 00:01:45.920 --> 00:01:48.709 align:start position:0% code uh this is important because we cannot<00:01:46.240> afford<00:01:46.960> having<00:01:47.240> some<00:01:47.560> Rust<00:01:48.079> case<00:01:48.399> bite 00:01:48.709 --> 00:01:48.719 align:start position:0% cannot afford having some Rust case bite 00:01:48.719 --> 00:01:51.429 align:start position:0% cannot afford having some Rust case bite codes<00:01:49.680> exploding<00:01:50.439> validation<00:01:51.000> time<00:01:51.240> and 00:01:51.429 --> 00:01:51.439 align:start position:0% codes exploding validation time and 00:01:51.439 --> 00:01:53.990 align:start position:0% codes exploding validation time and enabling<00:01:51.880> dos<00:01:52.320> attacks<00:01:52.960> with 00:01:53.990 --> 00:01:54.000 align:start position:0% enabling dos attacks with 00:01:54.000 --> 00:01:57.389 align:start position:0% enabling dos attacks with that<00:01:55.000> very<00:01:55.360> high<00:01:55.719> level<00:01:56.079> overview<00:01:56.520> of<00:01:56.719> how<00:01:57.119> St 00:01:57.389 --> 00:01:57.399 align:start position:0% that very high level overview of how St 00:01:57.399 --> 00:01:59.510 align:start position:0% that very high level overview of how St validation<00:01:57.799> would<00:01:58.000> work<00:01:58.399> we<00:01:59.039> go<00:01:59.280> through 00:01:59.510 --> 00:01:59.520 align:start position:0% validation would work we go through 00:01:59.520 --> 00:02:01.789 align:start position:0% validation would work we go through control<00:01:59.920> flow<00:02:00.119> of<00:02:00.240> the<00:02:00.399> graph<00:02:01.119> uh<00:02:01.360> control 00:02:01.789 --> 00:02:01.799 align:start position:0% control flow of the graph uh control 00:02:01.799 --> 00:02:04.990 align:start position:0% control flow of the graph uh control flow<00:02:02.159> graph<00:02:02.360> of<00:02:02.479> the<00:02:02.719> code<00:02:03.719> uh<00:02:04.000> examine<00:02:04.680> every 00:02:04.990 --> 00:02:05.000 align:start position:0% flow graph of the code uh examine every 00:02:05.000 --> 00:02:06.990 align:start position:0% flow graph of the code uh examine every instruction<00:02:05.439> and<00:02:05.560> see<00:02:05.840> how<00:02:06.000> many<00:02:06.280> values<00:02:06.680> it 00:02:06.990 --> 00:02:07.000 align:start position:0% instruction and see how many values it 00:02:07.000 --> 00:02:08.830 align:start position:0% instruction and see how many values it pushes<00:02:07.320> or<00:02:07.479> Pops<00:02:07.759> from<00:02:07.920> the<00:02:08.039> stack<00:02:08.360> and<00:02:08.599> keep 00:02:08.830 --> 00:02:08.840 align:start position:0% pushes or Pops from the stack and keep 00:02:08.840 --> 00:02:10.469 align:start position:0% pushes or Pops from the stack and keep track<00:02:09.119> of<00:02:09.440> what<00:02:09.560> is<00:02:09.720> the<00:02:09.840> current<00:02:10.119> stack 00:02:10.469 --> 00:02:10.479 align:start position:0% track of what is the current stack 00:02:10.479 --> 00:02:13.070 align:start position:0% track of what is the current stack height<00:02:10.720> if<00:02:10.840> it<00:02:11.039> ever<00:02:11.920> goes<00:02:12.239> below<00:02:12.560> zero<00:02:12.879> we 00:02:13.070 --> 00:02:13.080 align:start position:0% height if it ever goes below zero we 00:02:13.080 --> 00:02:15.949 align:start position:0% height if it ever goes below zero we detect<00:02:13.680> detect<00:02:14.000> underflow<00:02:14.760> if<00:02:14.879> it<00:02:15.040> ever<00:02:15.319> goes 00:02:15.949 --> 00:02:15.959 align:start position:0% detect detect underflow if it ever goes 00:02:15.959 --> 00:02:17.990 align:start position:0% detect detect underflow if it ever goes above<00:02:16.360> stack<00:02:16.680> height<00:02:16.879> limit<00:02:17.200> we<00:02:17.400> detect 00:02:17.990 --> 00:02:18.000 align:start position:0% above stack height limit we detect 00:02:18.000 --> 00:02:20.070 align:start position:0% above stack height limit we detect overflow<00:02:18.599> and<00:02:18.800> reject<00:02:19.160> this<00:02:19.360> entire<00:02:19.680> code<00:02:19.920> AS 00:02:20.070 --> 00:02:20.080 align:start position:0% overflow and reject this entire code AS 00:02:20.080 --> 00:02:23.990 align:start position:0% overflow and reject this entire code AS invalid<00:02:20.480> and<00:02:20.599> do<00:02:20.760> not<00:02:20.920> allow<00:02:21.239> to<00:02:22.120> for<00:02:22.319> it<00:02:22.440> to<00:02:22.560> be 00:02:23.990 --> 00:02:24.000 align:start position:0% invalid and do not allow to for it to be 00:02:24.000 --> 00:02:26.949 align:start position:0% invalid and do not allow to for it to be deployed<00:02:25.000> uh<00:02:25.160> this<00:02:25.519> sounds<00:02:26.120> pretty<00:02:26.440> simple 00:02:26.949 --> 00:02:26.959 align:start position:0% deployed uh this sounds pretty simple 00:02:26.959 --> 00:02:29.350 align:start position:0% deployed uh this sounds pretty simple and<00:02:27.200> high<00:02:27.400> level<00:02:27.879> and<00:02:28.080> you<00:02:28.239> might<00:02:28.480> wonder<00:02:29.200> at 00:02:29.350 --> 00:02:29.360 align:start position:0% and high level and you might wonder at 00:02:29.360 --> 00:02:31.470 align:start position:0% and high level and you might wonder at this<00:02:29.519> point<00:02:29.959> how<00:02:30.160> is<00:02:30.280> this<00:02:30.480> even<00:02:30.879> possible<00:02:31.239> to 00:02:31.470 --> 00:02:31.480 align:start position:0% this point how is this even possible to 00:02:31.480 --> 00:02:33.309 align:start position:0% this point how is this even possible to achieve<00:02:31.959> without<00:02:32.360> executing<00:02:32.840> the<00:02:32.959> code 00:02:33.309 --> 00:02:33.319 align:start position:0% achieve without executing the code 00:02:33.319 --> 00:02:35.869 align:start position:0% achieve without executing the code because<00:02:33.560> we<00:02:33.680> are<00:02:33.879> used<00:02:34.239> to<00:02:34.640> thinking<00:02:35.640> about 00:02:35.869 --> 00:02:35.879 align:start position:0% because we are used to thinking about 00:02:35.879 --> 00:02:38.869 align:start position:0% because we are used to thinking about underflows<00:02:36.440> and<00:02:36.599> overflows<00:02:37.319> as<00:02:38.040> depending<00:02:38.560> on 00:02:38.869 --> 00:02:38.879 align:start position:0% underflows and overflows as depending on 00:02:38.879 --> 00:02:42.509 align:start position:0% underflows and overflows as depending on the<00:02:39.640> runtime<00:02:40.640> uh<00:02:40.840> value<00:02:41.200> of<00:02:41.319> the<00:02:41.480> stack<00:02:41.840> height 00:02:42.509 --> 00:02:42.519 align:start position:0% the runtime uh value of the stack height 00:02:42.519 --> 00:02:45.270 align:start position:0% the runtime uh value of the stack height and<00:02:43.040> uh<00:02:43.200> depending<00:02:43.640> on<00:02:44.000> whatever<00:02:44.640> runtime 00:02:45.270 --> 00:02:45.280 align:start position:0% and uh depending on whatever runtime 00:02:45.280 --> 00:02:47.470 align:start position:0% and uh depending on whatever runtime conditions<00:02:45.560> on<00:02:45.920> call<00:02:46.200> data<00:02:46.440> or<00:02:46.720> storage<00:02:47.159> or 00:02:47.470 --> 00:02:47.480 align:start position:0% conditions on call data or storage or 00:02:47.480 --> 00:02:49.790 align:start position:0% conditions on call data or storage or whatever<00:02:48.480> I<00:02:48.560> will<00:02:48.720> show<00:02:48.920> you<00:02:49.120> that<00:02:49.319> in<00:02:49.480> fact 00:02:49.790 --> 00:02:49.800 align:start position:0% whatever I will show you that in fact 00:02:49.800 --> 00:02:51.990 align:start position:0% whatever I will show you that in fact this<00:02:49.920> is<00:02:50.239> possible<00:02:50.720> given<00:02:50.959> that<00:02:51.120> we<00:02:51.360> impose 00:02:51.990 --> 00:02:52.000 align:start position:0% this is possible given that we impose 00:02:52.000 --> 00:02:54.309 align:start position:0% this is possible given that we impose one<00:02:52.239> extra<00:02:52.560> restriction<00:02:53.080> on<00:02:53.519> what<00:02:53.680> is<00:02:53.920> allowed 00:02:54.309 --> 00:02:54.319 align:start position:0% one extra restriction on what is allowed 00:02:54.319 --> 00:02:57.630 align:start position:0% one extra restriction on what is allowed in<00:02:54.440> the<00:02:54.959> code<00:02:55.959> uh<00:02:56.080> so<00:02:56.319> let's<00:02:56.640> zoom<00:02:56.920> in<00:02:57.159> and 00:02:57.630 --> 00:02:57.640 align:start position:0% in the code uh so let's zoom in and 00:02:57.640 --> 00:03:00.350 align:start position:0% in the code uh so let's zoom in and explore<00:02:58.040> how<00:02:58.280> this<00:02:58.760> would<00:02:59.040> work 00:03:00.350 --> 00:03:00.360 align:start position:0% explore how this would work 00:03:00.360 --> 00:03:02.830 align:start position:0% explore how this would work this<00:03:00.519> was<00:03:00.800> our<00:03:01.280> initial<00:03:01.879> approach<00:03:02.280> to<00:03:02.480> this 00:03:02.830 --> 00:03:02.840 align:start position:0% this was our initial approach to this 00:03:02.840 --> 00:03:05.949 align:start position:0% this was our initial approach to this problem<00:03:03.720> um<00:03:04.200> and<00:03:04.760> let's<00:03:05.000> discuss<00:03:05.360> underflows 00:03:05.949 --> 00:03:05.959 align:start position:0% problem um and let's discuss underflows 00:03:05.959 --> 00:03:07.910 align:start position:0% problem um and let's discuss underflows first<00:03:06.319> uh<00:03:06.440> overflows<00:03:06.920> are<00:03:07.080> handled<00:03:07.599> quite 00:03:07.910 --> 00:03:07.920 align:start position:0% first uh overflows are handled quite 00:03:07.920 --> 00:03:10.070 align:start position:0% first uh overflows are handled quite differently<00:03:08.319> I<00:03:08.360> will<00:03:08.519> mention<00:03:08.840> this<00:03:09.040> later<00:03:09.879> so 00:03:10.070 --> 00:03:10.080 align:start position:0% differently I will mention this later so 00:03:10.080 --> 00:03:12.270 align:start position:0% differently I will mention this later so every<00:03:10.319> section<00:03:10.680> is<00:03:11.040> validated<00:03:11.640> independently 00:03:12.270 --> 00:03:12.280 align:start position:0% every section is validated independently 00:03:12.280 --> 00:03:14.750 align:start position:0% every section is validated independently one<00:03:12.480> section<00:03:12.720> at<00:03:12.840> a<00:03:13.000> time<00:03:13.799> uh<00:03:13.920> we<00:03:14.159> Traverse<00:03:14.640> the 00:03:14.750 --> 00:03:14.760 align:start position:0% one section at a time uh we Traverse the 00:03:14.760 --> 00:03:17.589 align:start position:0% one section at a time uh we Traverse the control<00:03:15.080> flow<00:03:15.400> graph<00:03:15.680> of<00:03:15.959> the<00:03:16.599> uh<00:03:16.799> code<00:03:17.360> in<00:03:17.480> a 00:03:17.589 --> 00:03:17.599 align:start position:0% control flow graph of the uh code in a 00:03:17.599 --> 00:03:19.110 align:start position:0% control flow graph of the uh code in a breadth<00:03:17.920> resarch<00:03:18.280> or<00:03:18.440> depth<00:03:18.640> res<00:03:18.840> search 00:03:19.110 --> 00:03:19.120 align:start position:0% breadth resarch or depth res search 00:03:19.120 --> 00:03:21.910 align:start position:0% breadth resarch or depth res search manner<00:03:19.760> meaning<00:03:20.120> we<00:03:20.280> follow<00:03:20.640> every<00:03:20.920> jump<00:03:21.760> uh 00:03:21.910 --> 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code AS 00:03:34.799 --> 00:03:37.229 align:start position:0% underflow and reject this code AS invalid<00:03:35.799> and<00:03:36.120> one<00:03:36.360> extra<00:03:36.680> restriction<00:03:37.080> that 00:03:37.229 --> 00:03:37.239 align:start position:0% invalid and one extra restriction that 00:03:37.239 --> 00:03:40.869 align:start position:0% invalid and one extra restriction that makes<00:03:37.400> it<00:03:37.560> all<00:03:37.799> possible<00:03:38.280> is<00:03:39.040> the<00:03:39.480> rule<00:03:40.480> if<00:03:40.640> we 00:03:40.869 --> 00:03:40.879 align:start position:0% makes it all possible is the rule if we 00:03:40.879 --> 00:03:43.750 align:start position:0% makes it all possible is the rule if we ever<00:03:41.720> uh<00:03:41.920> encounter<00:03:42.439> an<00:03:42.599> instruction<00:03:43.120> that 00:03:43.750 --> 00:03:43.760 align:start position:0% ever uh encounter an instruction that 00:03:43.760 --> 00:03:45.869 align:start position:0% ever uh encounter an instruction that during<00:03:44.040> out<00:03:44.280> reversal<00:03:44.799> that<00:03:45.120> was<00:03:45.400> already 00:03:45.869 --> 00:03:45.879 align:start position:0% during out reversal that was already 00:03:45.879 --> 00:03:48.990 align:start position:0% during out reversal that was already visited<00:03:46.879> before<00:03:47.879> uh<00:03:48.040> it<00:03:48.200> means<00:03:48.599> that<00:03:48.799> this 00:03:48.990 --> 00:03:49.000 align:start position:0% visited before uh it means that this 00:03:49.000 --> 00:03:51.110 align:start position:0% visited before uh it means that this instruction<00:03:49.519> may<00:03:49.680> be<00:03:49.840> reached<00:03:50.319> via<00:03:50.599> multiple 00:03:51.110 --> 00:03:51.120 align:start position:0% instruction may be reached via multiple 00:03:51.120 --> 00:03:53.990 align:start position:0% instruction may be reached via multiple possible<00:03:51.480> code<00:03:51.840> paths<00:03:52.120> during<00:03:52.480> execution<00:03:53.439> and 00:03:53.990 --> 00:03:54.000 align:start position:0% possible code paths during execution and 00:03:54.000 --> 00:03:56.229 align:start position:0% possible code paths during execution and uh<00:03:54.680> in<00:03:54.879> this<00:03:55.120> case<00:03:55.319> we<00:03:55.519> require<00:03:55.920> that<00:03:56.079> the 00:03:56.229 --> 00:03:56.239 align:start position:0% uh in this case we require that the 00:03:56.239 --> 00:03:58.110 align:start position:0% uh in this case we require that the stack<00:03:56.519> height<00:03:56.760> at<00:03:56.959> this<00:03:57.239> instruction<00:03:57.840> is 00:03:58.110 --> 00:03:58.120 align:start position:0% stack height at this instruction is 00:03:58.120 --> 00:04:00.630 align:start position:0% stack height at this instruction is equal<00:03:58.480> for<00:03:58.720> all<00:03:58.920> possible<00:03:59.280> code<00:03:59.560> P<00:03:59.959> leading<00:04:00.280> to 00:04:00.630 --> 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were possible in current 00:04:09.280 --> 00:04:12.830 align:start position:0% patterns that were possible in current evm<00:04:09.920> uh<00:04:10.040> invalid<00:04:10.640> now<00:04:10.920> in<00:04:11.439> eof<00:04:12.439> uh<00:04:12.560> as<00:04:12.640> a 00:04:12.830 --> 00:04:12.840 align:start position:0% evm uh invalid now in eof uh as a 00:04:12.840 --> 00:04:13.789 align:start position:0% evm uh invalid now in eof uh as a practical 00:04:13.789 --> 00:04:13.799 align:start position:0% practical 00:04:13.799 --> 00:04:16.830 align:start position:0% practical example<00:04:14.799> for<00:04:15.439> if<00:04:15.760> then<00:04:15.920> else<00:04:16.239> statement<00:04:16.720> you 00:04:16.830 --> 00:04:16.840 align:start position:0% example for if then else statement you 00:04:16.840 --> 00:04:18.629 align:start position:0% example for if then else statement you would<00:04:17.000> be<00:04:17.199> required<00:04:17.560> to<00:04:17.759> have<00:04:17.959> equal<00:04:18.239> stack 00:04:18.629 --> 00:04:18.639 align:start position:0% would be required to have equal stack 00:04:18.639 --> 00:04:20.590 align:start position:0% would be required to have equal stack height<00:04:19.079> at<00:04:19.199> the<00:04:19.320> end<00:04:19.519> of<00:04:19.680> the<00:04:19.959> than<00:04:20.160> and<00:04:20.320> else 00:04:20.590 --> 00:04:20.600 align:start position:0% height at the end of the than and else 00:04:20.600 --> 00:04:24.270 align:start position:0% height at the end of the than and else branches<00:04:21.160> for<00:04:21.440> example<00:04:22.440> or<00:04:22.800> for<00:04:23.280> Loops<00:04:24.040> for 00:04:24.270 --> 00:04:24.280 align:start position:0% branches for example or for Loops for 00:04:24.280 --> 00:04:26.749 align:start position:0% branches for example or for Loops for example<00:04:24.840> the<00:04:24.960> loop<00:04:25.360> body<00:04:25.800> is<00:04:25.960> not<00:04:26.199> allowed<00:04:26.560> to 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--> 00:04:35.629 align:start position:0% vmss also have similar rules like jvm and<00:04:34.400> web 00:04:35.629 --> 00:04:35.639 align:start position:0% and web 00:04:35.639 --> 00:04:38.110 align:start position:0% and web assembly<00:04:36.639> and<00:04:37.000> uh<00:04:37.120> thanks<00:04:37.320> to<00:04:37.479> this<00:04:37.680> rule<00:04:37.919> we 00:04:38.110 --> 00:04:38.120 align:start position:0% assembly and uh thanks to this rule we 00:04:38.120 --> 00:04:40.110 align:start position:0% assembly and uh thanks to this rule we just<00:04:38.440> when<00:04:38.639> we<00:04:39.080> get<00:04:39.240> to<00:04:39.400> the<00:04:39.560> branch<00:04:39.880> that<00:04:40.000> we 00:04:40.110 --> 00:04:40.120 align:start position:0% just when we get to the branch that we 00:04:40.120 --> 00:04:42.029 align:start position:0% just when we get to the branch that we have<00:04:40.280> already<00:04:40.479> seen<00:04:40.800> we<00:04:40.960> just<00:04:41.400> check<00:04:41.680> this 00:04:42.029 --> 00:04:42.039 align:start position:0% have already seen we just check this 00:04:42.039 --> 00:04:44.110 align:start position:0% have already seen we just check this condition<00:04:42.360> and<00:04:42.560> do<00:04:42.720> not<00:04:43.160> revalidate<00:04:43.800> the<00:04:43.919> same 00:04:44.110 --> 00:04:44.120 align:start position:0% condition and do not revalidate the same 00:04:44.120 --> 00:04:46.150 align:start position:0% condition and do not revalidate the same Branch<00:04:44.560> so<00:04:44.800> in<00:04:44.919> the<00:04:45.039> end<00:04:45.320> every<00:04:45.680> branch<00:04:46.000> is 00:04:46.150 --> 00:04:46.160 align:start position:0% Branch so in the end every branch is 00:04:46.160 --> 00:04:48.390 align:start position:0% Branch so in the end every branch is validated<00:04:46.759> exactly<00:04:47.160> once<00:04:47.520> every<00:04:47.759> instruction 00:04:48.390 --> 00:04:48.400 align:start position:0% validated exactly once every instruction 00:04:48.400 --> 00:04:51.510 align:start position:0% validated exactly once every instruction is<00:04:48.800> visited<00:04:49.600> exactly<00:04:50.039> once<00:04:50.400> so<00:04:50.720> complexity<00:04:51.320> is 00:04:51.510 --> 00:04:51.520 align:start position:0% is visited exactly once so complexity is 00:04:51.520 --> 00:04:53.550 align:start position:0% is visited exactly once so complexity is linear<00:04:52.000> for<00:04:52.240> this<00:04:52.400> algorithm<00:04:52.960> which<00:04:53.080> is<00:04:53.400> what 00:04:53.550 --> 00:04:53.560 align:start position:0% linear for this algorithm which is what 00:04:53.560 --> 00:04:57.110 align:start position:0% linear for this algorithm which is what we<00:04:53.840> desired<00:04:54.320> so<00:04:54.520> this<00:04:54.639> is<00:04:54.840> great<00:04:55.840> and<00:04:56.080> one<00:04:56.880> uh 00:04:57.110 --> 00:04:57.120 align:start position:0% we desired so this is great and one uh 00:04:57.120 --> 00:05:00.070 align:start position:0% we desired so this is great and one uh extra<00:04:57.479> rule<00:04:57.759> that<00:04:57.919> we<00:04:58.120> have<00:04:58.759> uh<00:04:58.960> if<00:04:59.240> after<00:04:59.880> the 00:05:00.070 --> 00:05:00.080 align:start position:0% extra rule that we have uh if after the 00:05:00.080 --> 00:05:01.710 align:start position:0% extra rule that we have uh if after the traval<00:05:00.560> is<00:05:00.680> finished<00:05:01.240> some<00:05:01.400> of<00:05:01.560> the 00:05:01.710 --> 00:05:01.720 align:start position:0% traval is finished some of the 00:05:01.720 --> 00:05:04.110 align:start position:0% traval is finished some of the instructions<00:05:02.280> are<00:05:02.520> not<00:05:02.919> visited<00:05:03.759> it<00:05:03.880> means 00:05:04.110 --> 00:05:04.120 align:start position:0% instructions are not visited it means 00:05:04.120 --> 00:05:06.469 align:start position:0% instructions are not visited it means they<00:05:04.240> are<00:05:04.400> never<00:05:04.639> going<00:05:04.840> to<00:05:04.960> be<00:05:05.120> reached<00:05:05.520> in<00:05:06.240> uh 00:05:06.469 --> 00:05:06.479 align:start position:0% they are never going to be reached in uh 00:05:06.479 --> 00:05:08.950 align:start position:0% they are never going to be reached in uh execution<00:05:07.360> and<00:05:07.800> we<00:05:07.919> do<00:05:08.080> not<00:05:08.240> allow<00:05:08.520> this<00:05:08.720> we<00:05:08.800> do 00:05:08.950 --> 00:05:08.960 align:start position:0% execution and we do not allow this we do 00:05:08.960 --> 00:05:10.430 align:start position:0% execution and we do not allow this we do not<00:05:09.120> allow<00:05:09.400> unreachable<00:05:09.960> code<00:05:10.199> to<00:05:10.280> be 00:05:10.430 --> 00:05:10.440 align:start position:0% not allow unreachable code to be 00:05:10.440 --> 00:05:12.430 align:start position:0% not allow unreachable code to be deployed<00:05:10.919> and<00:05:11.080> reject<00:05:11.440> an<00:05:11.639> entire<00:05:12.000> bite<00:05:12.240> code 00:05:12.430 --> 00:05:12.440 align:start position:0% deployed and reject an entire bite code 00:05:12.440 --> 00:05:13.390 align:start position:0% deployed and reject an entire bite code AS 00:05:13.390 --> 00:05:13.400 align:start position:0% AS 00:05:13.400 --> 00:05:15.710 align:start position:0% AS invalid<00:05:14.400> I'll<00:05:14.600> show<00:05:14.800> an<00:05:14.960> example<00:05:15.320> now<00:05:15.479> how 00:05:15.710 --> 00:05:15.720 align:start position:0% invalid I'll show an example now how 00:05:15.720 --> 00:05:19.270 align:start position:0% invalid I'll show an example now how this<00:05:15.880> would<00:05:16.440> work<00:05:17.440> here's<00:05:17.639> a<00:05:17.759> simple<00:05:18.160> code<00:05:19.160> uh 00:05:19.270 --> 00:05:19.280 align:start position:0% this would work here's a simple code uh 00:05:19.280 --> 00:05:20.950 align:start position:0% this would work here's a simple code uh we'll<00:05:19.479> need<00:05:19.680> an<00:05:19.840> array<00:05:20.160> of<00:05:20.280> Stack<00:05:20.600> Heights<00:05:20.800> for 00:05:20.950 --> 00:05:20.960 align:start position:0% we'll need an array of Stack Heights for 00:05:20.960 --> 00:05:23.790 align:start position:0% we'll need an array of Stack Heights for every<00:05:21.199> instruction<00:05:22.199> and<00:05:22.520> work<00:05:22.880> list<00:05:23.199> here<00:05:23.479> is 00:05:23.790 --> 00:05:23.800 align:start position:0% every instruction and work list here is 00:05:23.800 --> 00:05:25.830 align:start position:0% every instruction and work list here is a<00:05:24.240> q<00:05:24.520> like<00:05:24.720> data<00:05:24.919> structure<00:05:25.240> that<00:05:25.360> keeps<00:05:25.600> track 00:05:25.830 --> 00:05:25.840 align:start position:0% a q like data structure that keeps track 00:05:25.840 --> 00:05:28.390 align:start position:0% a q like data structure that keeps track of<00:05:26.080> which<00:05:26.440> branches<00:05:27.000> we<00:05:27.720> have<00:05:28.000> yet<00:05:28.240> to 00:05:28.390 --> 00:05:28.400 align:start position:0% of which branches we have yet to 00:05:28.400 --> 00:05:30.749 align:start position:0% of which branches we have yet to validate<00:05:28.919> so<00:05:29.080> we<00:05:29.199> start<00:05:29.440> with<00:05:30.039> first<00:05:30.319> Branch 00:05:30.749 --> 00:05:30.759 align:start position:0% validate so we start with first Branch 00:05:30.759 --> 00:05:33.870 align:start position:0% validate so we start with first Branch at<00:05:31.039> offset<00:05:31.560> zero<00:05:32.560> uh<00:05:32.720> push<00:05:33.000> instruction<00:05:33.560> would 00:05:33.870 --> 00:05:33.880 align:start position:0% at offset zero uh push instruction would 00:05:33.880 --> 00:05:36.749 align:start position:0% at offset zero uh push instruction would add<00:05:34.360> one<00:05:35.280> value<00:05:35.520> on<00:05:35.639> the<00:05:35.759> stack<00:05:36.240> uh<00:05:36.319> then<00:05:36.520> call 00:05:36.749 --> 00:05:36.759 align:start position:0% add one value on the stack uh then call 00:05:36.759 --> 00:05:38.510 align:start position:0% add one value on the stack uh then call data<00:05:37.000> load<00:05:37.240> doesn't<00:05:37.520> change<00:05:37.840> the<00:05:37.919> St<00:05:38.199> height 00:05:38.510 --> 00:05:38.520 align:start position:0% data load doesn't change the St height 00:05:38.520 --> 00:05:40.790 align:start position:0% data load doesn't change the St height then<00:05:38.759> this<00:05:39.120> conditional<00:05:39.360> jump<00:05:39.800> instruction 00:05:40.790 --> 00:05:40.800 align:start position:0% then this conditional jump instruction 00:05:40.800 --> 00:05:44.189 align:start position:0% then this conditional jump instruction has<00:05:41.080> two<00:05:41.479> possible<00:05:42.560> successors<00:05:43.560> at<00:05:43.759> offsets 00:05:44.189 --> 00:05:44.199 align:start position:0% has two possible successors at offsets 00:05:44.199 --> 00:05:46.270 align:start position:0% has two possible successors at offsets 10<00:05:44.360> and<00:05:44.560> five<00:05:44.880> we<00:05:45.120> add<00:05:45.360> them<00:05:45.520> both<00:05:45.919> into<00:05:46.160> the 00:05:46.270 --> 00:05:46.280 align:start position:0% 10 and five we add them both into the 00:05:46.280 --> 00:05:48.430 align:start position:0% 10 and five we add them both into the work<00:05:46.560> list<00:05:47.000> and<00:05:47.319> at<00:05:47.479> this<00:05:47.720> point<00:05:47.919> we<00:05:48.080> also<00:05:48.319> have 00:05:48.430 --> 00:05:48.440 align:start position:0% work list and at this point we also have 00:05:48.440 --> 00:05:51.350 align:start position:0% work list and at this point we also have to<00:05:48.600> record<00:05:49.199> the<00:05:49.360> stack<00:05:49.800> height<00:05:50.800> uh<00:05:50.919> at<00:05:51.080> both<00:05:51.280> of 00:05:51.350 --> 00:05:51.360 align:start position:0% to record the stack height uh at both of 00:05:51.360 --> 00:05:53.270 align:start position:0% to record the stack height uh at both of the<00:05:51.479> targets<00:05:52.039> stack<00:05:52.319> height<00:05:52.520> is<00:05:52.639> zero<00:05:52.880> after<00:05:53.080> R 00:05:53.270 --> 00:05:53.280 align:start position:0% the targets stack height is zero after R 00:05:53.280 --> 00:05:56.189 align:start position:0% the targets stack height is zero after R jump<00:05:53.520> I<00:05:53.759> so<00:05:53.919> we<00:05:54.039> record<00:05:54.479> that<00:05:54.840> at<00:05:55.039> both<00:05:55.360> offsets 00:05:56.189 --> 00:05:56.199 align:start position:0% jump I so we record that at both offsets 00:05:56.199 --> 00:05:58.790 align:start position:0% jump I so we record that at both offsets and<00:05:56.400> continue<00:05:57.080> then<00:05:57.479> with<00:05:57.680> the<00:05:58.160> next<00:05:58.440> Branch 00:05:58.790 --> 00:05:58.800 align:start position:0% and continue then with the next Branch 00:05:58.800 --> 00:06:00.590 align:start position:0% and continue then with the next Branch from<00:05:58.919> the<00:05:59.039> work<00:05:59.280> list<00:05:59.440> we<00:05:59.680> go<00:05:59.800> to<00:05:59.960> offset<00:06:00.280> zero 00:06:00.590 --> 00:06:00.600 align:start position:0% from the work list we go to offset zero 00:06:00.600 --> 00:06:02.430 align:start position:0% from the work list we go to offset zero there<00:06:00.759> there's<00:06:00.960> a<00:06:01.080> push<00:06:01.319> and<00:06:01.479> another<00:06:01.800> push 00:06:02.430 --> 00:06:02.440 align:start position:0% there there's a push and another push 00:06:02.440 --> 00:06:05.550 align:start position:0% there there's a push and another push then<00:06:02.639> a<00:06:02.880> store<00:06:03.560> checks<00:06:04.560> whether<00:06:05.080> it<00:06:05.280> has 00:06:05.550 --> 00:06:05.560 align:start position:0% then a store checks whether it has 00:06:05.560 --> 00:06:08.550 align:start position:0% then a store checks whether it has enough<00:06:05.960> items<00:06:06.440> not<00:06:06.599> to<00:06:06.800> under 00:06:08.550 --> 00:06:08.560 align:start position:0% enough items not to under 00:06:08.560 --> 00:06:11.670 align:start position:0% enough items not to under underflow<00:06:09.560> uh<00:06:10.000> two<00:06:10.280> is<00:06:10.400> exactly<00:06:10.800> enough<00:06:11.039> for<00:06:11.400> S 00:06:11.670 --> 00:06:11.680 align:start position:0% underflow uh two is exactly enough for S 00:06:11.680 --> 00:06:13.710 align:start position:0% underflow uh two is exactly enough for S stor<00:06:12.120> so<00:06:12.360> no<00:06:12.520> underlow<00:06:13.000> happens<00:06:13.280> we<00:06:13.360> are<00:06:13.479> good 00:06:13.710 --> 00:06:13.720 align:start position:0% stor so no underlow happens we are good 00:06:13.720 --> 00:06:17.029 align:start position:0% stor so no underlow happens we are good here<00:06:14.160> and<00:06:14.360> we<00:06:14.560> continue<00:06:15.560> uh<00:06:16.199> this<00:06:16.479> stop<00:06:16.840> then 00:06:17.029 --> 00:06:17.039 align:start position:0% here and we continue uh this stop then 00:06:17.039 --> 00:06:19.870 align:start position:0% here and we continue uh this stop then validates<00:06:17.919> uh<00:06:18.240> uh<00:06:18.800> concludes<00:06:19.280> validation<00:06:19.680> of 00:06:19.870 --> 00:06:19.880 align:start position:0% validates uh uh concludes validation of 00:06:19.880 --> 00:06:22.550 align:start position:0% validates uh uh concludes validation of this<00:06:20.080> branch<00:06:21.000> and<00:06:21.160> we<00:06:21.319> have<00:06:21.520> still<00:06:21.800> one<00:06:22.199> branch 00:06:22.550 --> 00:06:22.560 align:start position:0% this branch and we have still one branch 00:06:22.560 --> 00:06:24.790 align:start position:0% this branch and we have still one branch left<00:06:22.759> to<00:06:23.000> examine<00:06:23.599> at<00:06:23.759> offset<00:06:24.199> five<00:06:24.440> we<00:06:24.560> go 00:06:24.790 --> 00:06:24.800 align:start position:0% left to examine at offset five we go 00:06:24.800 --> 00:06:26.950 align:start position:0% left to examine at offset five we go there<00:06:25.080> there's<00:06:25.440> another<00:06:25.720> push<00:06:26.080> and<00:06:26.280> then 00:06:26.950 --> 00:06:26.960 align:start position:0% there there's another push and then 00:06:26.960 --> 00:06:28.749 align:start position:0% there there's another push and then another<00:06:27.319> jump<00:06:27.680> into<00:06:27.960> the<00:06:28.160> Target<00:06:28.520> that<00:06:28.639> we 00:06:28.749 --> 00:06:28.759 align:start position:0% another jump into the Target that we 00:06:28.759 --> 00:06:30.309 align:start position:0% another jump into the Target that we have<00:06:28.919> already<00:06:29.199> visited<00:06:29.680> before<00:06:29.960> at<00:06:30.120> this 00:06:30.309 --> 00:06:30.319 align:start position:0% have already visited before at this 00:06:30.319 --> 00:06:31.710 align:start position:0% have already visited before at this point<00:06:30.560> we<00:06:30.680> have<00:06:30.800> to<00:06:30.960> check<00:06:31.199> whether<00:06:31.440> current 00:06:31.710 --> 00:06:31.720 align:start position:0% point we have to check whether current 00:06:31.720 --> 00:06:34.029 align:start position:0% point we have to check whether current stack<00:06:32.039> height<00:06:32.319> is<00:06:32.479> equal<00:06:32.759> to<00:06:33.599> what<00:06:33.759> we<00:06:33.880> have 00:06:34.029 --> 00:06:34.039 align:start position:0% stack height is equal to what we have 00:06:34.039 --> 00:06:37.270 align:start position:0% stack height is equal to what we have recorded<00:06:34.840> for<00:06:35.160> this<00:06:35.639> target<00:06:36.080> before<00:06:36.400> it<00:06:36.560> was 00:06:37.270 --> 00:06:37.280 align:start position:0% recorded for this target before it was 00:06:37.280 --> 00:06:39.670 align:start position:0% recorded for this target before it was one<00:06:37.720> previously<00:06:38.319> and<00:06:38.680> stack<00:06:39.080> height<00:06:39.280> is<00:06:39.440> also 00:06:39.670 --> 00:06:39.680 align:start position:0% one previously and stack height is also 00:06:39.680 --> 00:06:42.309 align:start position:0% one previously and stack height is also one<00:06:39.919> for<00:06:40.160> this<00:06:40.880> after<00:06:41.160> this<00:06:41.319> R<00:06:41.560> jump<00:06:41.880> so<00:06:42.080> 1 00:06:42.309 --> 00:06:42.319 align:start position:0% one for this after this R jump so 1 00:06:42.319 --> 00:06:46.070 align:start position:0% one for this after this R jump so 1 equals<00:06:43.280> one<00:06:44.280> and<00:06:44.919> uh<00:06:45.080> so<00:06:45.280> this<00:06:45.360> is<00:06:45.599> valid<00:06:45.840> we<00:06:45.960> do 00:06:46.070 --> 00:06:46.080 align:start position:0% equals one and uh so this is valid we do 00:06:46.080 --> 00:06:48.230 align:start position:0% equals one and uh so this is valid we do not<00:06:46.360> revisit<00:06:46.880> this<00:06:47.039> Branch<00:06:47.440> anymore<00:06:47.919> and<00:06:48.080> then 00:06:48.230 --> 00:06:48.240 align:start position:0% not revisit this Branch anymore and then 00:06:48.240 --> 00:06:49.589 align:start position:0% not revisit this Branch anymore and then we<00:06:48.319> do<00:06:48.440> not<00:06:48.599> have<00:06:48.759> anything<00:06:49.000> else<00:06:49.160> in<00:06:49.240> the<00:06:49.360> work 00:06:49.589 --> 00:06:49.599 align:start position:0% we do not have anything else in the work 00:06:49.599 --> 00:06:51.390 align:start position:0% we do not have anything else in the work list<00:06:50.000> and<00:06:50.240> this<00:06:50.440> concludes<00:06:50.840> the<00:06:50.960> validation 00:06:51.390 --> 00:06:51.400 align:start position:0% list and this concludes the validation 00:06:51.400 --> 00:06:53.589 align:start position:0% list and this concludes the validation this<00:06:51.560> code<00:06:51.759> is<00:06:51.919> valid<00:06:52.160> in<00:06:52.240> the<00:06:52.360> end<00:06:53.199> compare 00:06:53.589 --> 00:06:53.599 align:start position:0% this code is valid in the end compare 00:06:53.599 --> 00:06:56.230 align:start position:0% this code is valid in the end compare this<00:06:53.759> to<00:06:53.960> this<00:06:54.240> invalid<00:06:55.199> code<00:06:55.680> it<00:06:55.800> is<00:06:56.039> very 00:06:56.230 --> 00:06:56.240 align:start position:0% this to this invalid code it is very 00:06:56.240 --> 00:06:58.749 align:start position:0% this to this invalid code it is very similar<00:06:56.599> but<00:06:56.800> with<00:06:56.960> one<00:06:57.199> push<00:06:57.520> emitted<00:06:58.280> uh<00:06:58.520> so 00:06:58.749 --> 00:06:58.759 align:start position:0% similar but with one push emitted uh so 00:06:58.759 --> 00:07:01.270 align:start position:0% similar but with one push emitted uh so it<00:06:58.879> goes<00:06:59.120> through<00:06:59.319> very<00:06:59.720> similar<00:07:00.160> steps<00:07:00.639> and 00:07:01.270 --> 00:07:01.280 align:start position:0% it goes through very similar steps and 00:07:01.280 --> 00:07:03.469 align:start position:0% it goes through very similar steps and ends<00:07:01.639> up<00:07:01.919> at<00:07:02.120> this<00:07:02.360> R<00:07:02.680> jump 00:07:03.469 --> 00:07:03.479 align:start position:0% ends up at this R jump 00:07:03.479 --> 00:07:05.550 align:start position:0% ends up at this R jump instruction<00:07:04.479> uh<00:07:04.599> and<00:07:04.759> at<00:07:04.879> this<00:07:05.039> point<00:07:05.240> stack 00:07:05.550 --> 00:07:05.560 align:start position:0% instruction uh and at this point stack 00:07:05.560 --> 00:07:07.909 align:start position:0% instruction uh and at this point stack height<00:07:05.759> is<00:07:05.919> zero<00:07:06.360> but<00:07:06.520> we<00:07:06.680> have<00:07:06.879> seen<00:07:07.599> stack 00:07:07.909 --> 00:07:07.919 align:start position:0% height is zero but we have seen stack 00:07:07.919 --> 00:07:10.309 align:start position:0% height is zero but we have seen stack height<00:07:08.160> one<00:07:08.440> at<00:07:08.560> the<00:07:08.720> Target<00:07:09.120> before<00:07:09.720> and<00:07:10.120> so 00:07:10.309 --> 00:07:10.319 align:start position:0% height one at the Target before and so 00:07:10.319 --> 00:07:12.430 align:start position:0% height one at the Target before and so they<00:07:10.440> are<00:07:10.560> not<00:07:10.680> equal<00:07:11.080> and<00:07:11.319> this<00:07:11.879> means<00:07:12.240> code 00:07:12.430 --> 00:07:12.440 align:start position:0% they are not equal and this means code 00:07:12.440 --> 00:07:14.270 align:start position:0% they are not equal and this means code is<00:07:12.560> invalid<00:07:12.919> and 00:07:14.270 --> 00:07:14.280 align:start position:0% is invalid and 00:07:14.280 --> 00:07:17.430 align:start position:0% is invalid and rejected<00:07:15.280> so<00:07:15.720> this<00:07:16.120> uh<00:07:16.280> exact<00:07:16.840> restriction 00:07:17.430 --> 00:07:17.440 align:start position:0% rejected so this uh exact restriction 00:07:17.440 --> 00:07:19.150 align:start position:0% rejected so this uh exact restriction that<00:07:17.560> makes<00:07:17.759> it<00:07:17.879> all<00:07:18.120> possible<00:07:18.639> uh<00:07:18.720> turned<00:07:19.000> out 00:07:19.150 --> 00:07:19.160 align:start position:0% that makes it all possible uh turned out 00:07:19.160 --> 00:07:21.469 align:start position:0% that makes it all possible uh turned out to<00:07:19.280> be<00:07:19.440> problematic<00:07:19.919> in<00:07:20.080> some<00:07:20.280> important 00:07:21.469 --> 00:07:21.479 align:start position:0% to be problematic in some important 00:07:21.479 --> 00:07:25.469 align:start position:0% to be problematic in some important cases<00:07:22.479> so<00:07:22.720> this<00:07:22.879> code<00:07:23.360> like<00:07:23.720> on<00:07:23.840> the<00:07:24.319> slide<00:07:25.319> uh 00:07:25.469 --> 00:07:25.479 align:start position:0% cases so this code like on the slide uh 00:07:25.479 --> 00:07:28.589 align:start position:0% cases so this code like on the slide uh can<00:07:25.720> be<00:07:26.360> commonly<00:07:27.120> generated<00:07:27.800> by<00:07:28.039> solidity 00:07:28.589 --> 00:07:28.599 align:start position:0% can be commonly generated by solidity 00:07:28.599 --> 00:07:30.309 align:start position:0% can be commonly generated by solidity for<00:07:28.800> example<00:07:29.080> when<00:07:29.199> you<00:07:29.319> have<00:07:29.599> a<00:07:29.759> series<00:07:30.080> of 00:07:30.309 --> 00:07:30.319 align:start position:0% for example when you have a series of 00:07:30.319 --> 00:07:32.749 align:start position:0% for example when you have a series of requir<00:07:30.720> statements<00:07:31.080> in<00:07:31.240> solidity<00:07:31.840> every 00:07:32.749 --> 00:07:32.759 align:start position:0% requir statements in solidity every 00:07:32.759 --> 00:07:35.189 align:start position:0% requir statements in solidity every require<00:07:33.280> is<00:07:33.759> a<00:07:33.960> check<00:07:34.240> and<00:07:34.440> revert<00:07:34.919> in<00:07:35.039> case 00:07:35.189 --> 00:07:35.199 align:start position:0% require is a check and revert in case 00:07:35.199 --> 00:07:38.189 align:start position:0% require is a check and revert in case it's<00:07:35.400> not<00:07:36.280> uh<00:07:36.440> satisfied<00:07:37.199> and<00:07:37.400> then<00:07:38.080> uh 00:07:38.189 --> 00:07:38.199 align:start position:0% it's not uh satisfied and then uh 00:07:38.199 --> 00:07:40.430 align:start position:0% it's not uh satisfied and then uh solidity<00:07:38.680> Optimizer<00:07:39.240> at<00:07:39.360> some<00:07:39.560> point 00:07:40.430 --> 00:07:40.440 align:start position:0% solidity Optimizer at some point 00:07:40.440 --> 00:07:43.070 align:start position:0% solidity Optimizer at some point extracts<00:07:41.000> these<00:07:41.280> reverts<00:07:41.759> into<00:07:41.960> a<00:07:42.199> common<00:07:42.960> uh 00:07:43.070 --> 00:07:43.080 align:start position:0% extracts these reverts into a common uh 00:07:43.080 --> 00:07:46.189 align:start position:0% extracts these reverts into a common uh code<00:07:43.680> uh<00:07:43.840> common<00:07:44.120> code<00:07:44.360> block<00:07:45.120> and<00:07:45.440> uh<00:07:45.879> then 00:07:46.189 --> 00:07:46.199 align:start position:0% code uh common code block and uh then 00:07:46.199 --> 00:07:48.070 align:start position:0% code uh common code block and uh then each<00:07:46.560> require<00:07:47.000> becomes<00:07:47.400> this<00:07:47.599> check<00:07:47.800> anded 00:07:48.070 --> 00:07:48.080 align:start position:0% each require becomes this check anded 00:07:48.080 --> 00:07:50.909 align:start position:0% each require becomes this check anded jump<00:07:48.479> into<00:07:48.720> this<00:07:48.919> common<00:07:49.400> code<00:07:50.400> uh<00:07:50.520> so<00:07:50.759> the 00:07:50.909 --> 00:07:50.919 align:start position:0% jump into this common code uh so the 00:07:50.919 --> 00:07:53.749 align:start position:0% jump into this common code uh so the problem<00:07:51.280> here<00:07:52.240> these<00:07:52.680> uh<00:07:52.840> requires<00:07:53.479> and<00:07:53.599> these 00:07:53.749 --> 00:07:53.759 align:start position:0% problem here these uh requires and these 00:07:53.759 --> 00:07:55.830 align:start position:0% problem here these uh requires and these checks<00:07:54.000> and<00:07:54.159> jumps<00:07:54.520> can<00:07:54.919> be<00:07:55.159> located<00:07:55.639> at 00:07:55.830 --> 00:07:55.840 align:start position:0% checks and jumps can be located at 00:07:55.840 --> 00:07:57.950 align:start position:0% checks and jumps can be located at arbitary<00:07:56.400> points<00:07:56.680> in<00:07:56.800> the<00:07:56.919> function<00:07:57.319> code<00:07:57.720> and 00:07:57.950 --> 00:07:57.960 align:start position:0% arbitary points in the function code and 00:07:57.960 --> 00:08:01.589 align:start position:0% arbitary points in the function code and at<00:07:58.159> arbitary<00:07:58.720> stack<00:07:59.080> Heights<00:07:59.800> and<00:08:00.759> this<00:08:01.120> goes 00:08:01.589 --> 00:08:01.599 align:start position:0% at arbitary stack Heights and this goes 00:08:01.599 --> 00:08:03.230 align:start position:0% at arbitary stack Heights and this goes specifically<00:08:02.120> against<00:08:02.400> our<00:08:02.599> rule<00:08:02.840> that<00:08:02.960> stack 00:08:03.230 --> 00:08:03.240 align:start position:0% specifically against our rule that stack 00:08:03.240 --> 00:08:04.990 align:start position:0% specifically against our rule that stack height<00:08:03.440> must<00:08:03.599> be<00:08:03.759> equal<00:08:04.080> at 00:08:04.990 --> 00:08:05.000 align:start position:0% height must be equal at 00:08:05.000 --> 00:08:08.990 align:start position:0% height must be equal at every<00:08:06.000> every<00:08:06.400> jump<00:08:06.759> into<00:08:07.360> uh<00:08:07.759> common 00:08:08.990 --> 00:08:09.000 align:start position:0% every every jump into uh common 00:08:09.000 --> 00:08:12.270 align:start position:0% every every jump into uh common code<00:08:10.000> uh<00:08:10.840> compilers<00:08:11.479> could<00:08:11.680> deal<00:08:11.919> with<00:08:12.080> it 00:08:12.270 --> 00:08:12.280 align:start position:0% code uh compilers could deal with it 00:08:12.280 --> 00:08:14.589 align:start position:0% code uh compilers could deal with it with<00:08:12.440> some<00:08:12.680> workarounds<00:08:13.599> for<00:08:13.759> example<00:08:14.400> they 00:08:14.589 --> 00:08:14.599 align:start position:0% with some workarounds for example they 00:08:14.599 --> 00:08:16.749 align:start position:0% with some workarounds for example they could<00:08:15.080> uh<00:08:15.199> insert<00:08:15.919> some<00:08:16.159> extra<00:08:16.520> Pop 00:08:16.749 --> 00:08:16.759 align:start position:0% could uh insert some extra Pop 00:08:16.759 --> 00:08:18.230 align:start position:0% could uh insert some extra Pop instructions<00:08:17.199> before<00:08:17.440> some<00:08:17.680> jumps<00:08:18.000> to 00:08:18.230 --> 00:08:18.240 align:start position:0% instructions before some jumps to 00:08:18.240 --> 00:08:19.909 align:start position:0% instructions before some jumps to equalize<00:08:18.680> the<00:08:18.840> stack<00:08:19.039> and<00:08:19.199> make<00:08:19.319> it<00:08:19.479> equal<00:08:19.720> for 00:08:19.909 --> 00:08:19.919 align:start position:0% equalize the stack and make it equal for 00:08:19.919 --> 00:08:22.350 align:start position:0% equalize the stack and make it equal for every<00:08:20.159> jump<00:08:20.440> into<00:08:20.599> a<00:08:20.720> common<00:08:21.000> code<00:08:22.000> but<00:08:22.240> this 00:08:22.350 --> 00:08:22.360 align:start position:0% every jump into a common code but this 00:08:22.360 --> 00:08:24.909 align:start position:0% every jump into a common code but this would<00:08:22.560> mean<00:08:22.919> increased<00:08:23.560> code<00:08:23.919> size<00:08:24.599> and 00:08:24.909 --> 00:08:24.919 align:start position:0% would mean increased code size and 00:08:24.919 --> 00:08:28.230 align:start position:0% would mean increased code size and increased<00:08:25.360> gas<00:08:25.599> consumed<00:08:26.440> so<00:08:27.000> this<00:08:27.319> entire 00:08:28.230 --> 00:08:28.240 align:start position:0% increased gas consumed so this entire 00:08:28.240 --> 00:08:29.950 align:start position:0% increased gas consumed so this entire optimization<00:08:28.840> might<00:08:29.039> not<00:08:29.159> be<00:08:29.520> worth<00:08:29.720> it<00:08:29.879> in 00:08:29.950 --> 00:08:29.960 align:start position:0% optimization might not be worth it in 00:08:29.960 --> 00:08:32.630 align:start position:0% optimization might not be worth it in the<00:08:30.280> end<00:08:31.280> or<00:08:31.479> another<00:08:31.720> workaround<00:08:32.279> could<00:08:32.440> be 00:08:32.630 --> 00:08:32.640 align:start position:0% the end or another workaround could be 00:08:32.640 --> 00:08:35.190 align:start position:0% the end or another workaround could be to<00:08:32.959> take<00:08:33.159> this<00:08:33.399> revert<00:08:33.880> and<00:08:34.039> make<00:08:34.240> an<00:08:34.839> uh 00:08:35.190 --> 00:08:35.200 align:start position:0% to take this revert and make an uh 00:08:35.200 --> 00:08:37.029 align:start position:0% to take this revert and make an uh separate<00:08:35.599> code<00:08:35.839> section<00:08:36.159> out<00:08:36.279> of<00:08:36.440> it<00:08:36.680> and<00:08:36.839> call 00:08:37.029 --> 00:08:37.039 align:start position:0% separate code section out of it and call 00:08:37.039 --> 00:08:39.750 align:start position:0% separate code section out of it and call it<00:08:37.159> from<00:08:37.399> here<00:08:37.880> this<00:08:38.000> would<00:08:38.200> also<00:08:38.479> work<00:08:38.959> but 00:08:39.750 --> 00:08:39.760 align:start position:0% it from here this would also work but 00:08:39.760 --> 00:08:44.149 align:start position:0% it from here this would also work but this<00:08:40.000> also<00:08:40.320> has<00:08:40.440> an<00:08:40.640> overhead<00:08:41.320> of<00:08:42.120> um<00:08:43.159> putting 00:08:44.149 --> 00:08:44.159 align:start position:0% this also has an overhead of um putting 00:08:44.159 --> 00:08:46.030 align:start position:0% this also has an overhead of um putting declaring<00:08:44.680> this<00:08:44.920> extra<00:08:45.279> code<00:08:45.560> section<00:08:45.760> in<00:08:45.920> the 00:08:46.030 --> 00:08:46.040 align:start position:0% declaring this extra code section in the 00:08:46.040 --> 00:08:48.389 align:start position:0% declaring this extra code section in the UF<00:08:46.440> header<00:08:46.880> putting<00:08:47.200> its<00:08:47.360> metadata<00:08:47.800> into<00:08:48.080> type 00:08:48.389 --> 00:08:48.399 align:start position:0% UF header putting its metadata into type 00:08:48.399 --> 00:08:50.990 align:start position:0% UF header putting its metadata into type section<00:08:49.399> so<00:08:49.600> in<00:08:49.720> the<00:08:49.839> end<00:08:50.160> code<00:08:50.440> size<00:08:50.640> also<00:08:50.880> is 00:08:50.990 --> 00:08:51.000 align:start position:0% section so in the end code size also is 00:08:51.000 --> 00:08:52.590 align:start position:0% section so in the end code size also is increased<00:08:51.560> and<00:08:51.760> we<00:08:51.920> might<00:08:52.160> have<00:08:52.399> some 00:08:52.590 --> 00:08:52.600 align:start position:0% increased and we might have some 00:08:52.600 --> 00:08:54.870 align:start position:0% increased and we might have some regressions<00:08:53.240> comparing<00:08:53.680> to<00:08:54.040> current<00:08:54.360> evm 00:08:54.870 --> 00:08:54.880 align:start position:0% regressions comparing to current evm 00:08:54.880 --> 00:08:56.310 align:start position:0% regressions comparing to current evm this<00:08:54.959> is<00:08:55.160> something<00:08:55.519> we<00:08:55.800> really<00:08:56.000> would<00:08:56.200> like 00:08:56.310 --> 00:08:56.320 align:start position:0% this is something we really would like 00:08:56.320 --> 00:08:59.230 align:start position:0% this is something we really would like to<00:08:56.920> avoid<00:08:57.920> uh<00:08:58.200> and<00:08:58.360> this<00:08:58.480> is<00:08:58.640> just<00:08:58.800> one<00:08:59.000> common 00:08:59.230 --> 00:08:59.240 align:start position:0% to avoid uh and this is just one common 00:08:59.240 --> 00:09:01.230 align:start position:0% to avoid uh and this is just one common examp<00:08:59.480> example<00:08:59.839> it's<00:09:00.040> not<00:09:00.200> the<00:09:00.320> only<00:09:00.560> one<00:09:01.120> in 00:09:01.230 --> 00:09:01.240 align:start position:0% examp example it's not the only one in 00:09:01.240 --> 00:09:04.870 align:start position:0% examp example it's not the only one in general<00:09:01.800> compilers<00:09:02.360> are<00:09:02.560> very<00:09:02.800> much<00:09:03.600> um<00:09:04.560> uh<00:09:04.680> in 00:09:04.870 --> 00:09:04.880 align:start position:0% general compilers are very much um uh in 00:09:04.880 --> 00:09:08.550 align:start position:0% general compilers are very much um uh in favor<00:09:05.200> of<00:09:05.560> being<00:09:06.079> able<00:09:06.680> to<00:09:07.560> jump<00:09:07.959> into<00:09:08.240> some 00:09:08.550 --> 00:09:08.560 align:start position:0% favor of being able to jump into some 00:09:08.560 --> 00:09:11.230 align:start position:0% favor of being able to jump into some common<00:09:09.320> uh<00:09:09.760> helper<00:09:10.240> code<00:09:10.519> blocks<00:09:11.000> from 00:09:11.230 --> 00:09:11.240 align:start position:0% common uh helper code blocks from 00:09:11.240 --> 00:09:12.949 align:start position:0% common uh helper code blocks from arbitrary<00:09:11.760> stack 00:09:12.949 --> 00:09:12.959 align:start position:0% arbitrary stack 00:09:12.959 --> 00:09:15.829 align:start position:0% arbitrary stack Heights<00:09:13.959> so<00:09:14.160> we<00:09:14.279> found<00:09:14.600> a<00:09:14.800> solution<00:09:15.399> to<00:09:15.600> this 00:09:15.829 --> 00:09:15.839 align:start position:0% Heights so we found a solution to this 00:09:15.839 --> 00:09:18.150 align:start position:0% Heights so we found a solution to this and<00:09:16.000> this<00:09:16.120> is<00:09:16.320> current<00:09:16.600> spec<00:09:16.839> of<00:09:16.959> 50450<00:09:17.760> and 00:09:18.150 --> 00:09:18.160 align:start position:0% and this is current spec of 50450 and 00:09:18.160 --> 00:09:21.470 align:start position:0% and this is current spec of 50450 and final<00:09:18.720> one<00:09:19.720> uh<00:09:20.040> so<00:09:20.279> we<00:09:20.440> have<00:09:20.600> to<00:09:20.760> modify<00:09:21.240> our 00:09:21.470 --> 00:09:21.480 align:start position:0% final one uh so we have to modify our 00:09:21.480 --> 00:09:23.470 align:start position:0% final one uh so we have to modify our algorithm<00:09:22.360> somewhat<00:09:22.800> in<00:09:22.920> some<00:09:23.079> important 00:09:23.470 --> 00:09:23.480 align:start position:0% algorithm somewhat in some important 00:09:23.480 --> 00:09:26.670 align:start position:0% algorithm somewhat in some important ways<00:09:24.480> uh<00:09:25.480> uh<00:09:25.560> we<00:09:25.720> start<00:09:26.000> with<00:09:26.160> allowing 00:09:26.670 --> 00:09:26.680 align:start position:0% ways uh uh we start with allowing 00:09:26.680 --> 00:09:28.150 align:start position:0% ways uh uh we start with allowing multiple<00:09:27.120> possible<00:09:27.399> stack<00:09:27.720> Heights<00:09:27.959> for 00:09:28.150 --> 00:09:28.160 align:start position:0% multiple possible stack Heights for 00:09:28.160 --> 00:09:30.350 align:start position:0% multiple possible stack Heights for every<00:09:28.399> instruction<00:09:29.040> in<00:09:29.360> instead<00:09:29.600> of<00:09:30.240> uh 00:09:30.350 --> 00:09:30.360 align:start position:0% every instruction in instead of uh 00:09:30.360 --> 00:09:32.470 align:start position:0% every instruction in instead of uh recording<00:09:30.880> just<00:09:31.040> one<00:09:31.240> stack<00:09:31.560> height<00:09:31.800> value<00:09:32.279> we 00:09:32.470 --> 00:09:32.480 align:start position:0% recording just one stack height value we 00:09:32.480 --> 00:09:34.750 align:start position:0% recording just one stack height value we record<00:09:33.360> uh<00:09:33.560> the<00:09:33.680> range<00:09:33.959> of<00:09:34.079> Stack<00:09:34.360> Heights<00:09:34.560> to 00:09:34.750 --> 00:09:34.760 align:start position:0% record uh the range of Stack Heights to 00:09:34.760 --> 00:09:36.509 align:start position:0% record uh the range of Stack Heights to minimum<00:09:35.160> and<00:09:35.360> maximum<00:09:35.959> for<00:09:36.200> every 00:09:36.509 --> 00:09:36.519 align:start position:0% minimum and maximum for every 00:09:36.519 --> 00:09:38.470 align:start position:0% minimum and maximum for every instruction<00:09:37.519> we<00:09:37.640> change<00:09:37.920> the<00:09:38.040> way<00:09:38.240> we 00:09:38.470 --> 00:09:38.480 align:start position:0% instruction we change the way we 00:09:38.480 --> 00:09:41.310 align:start position:0% instruction we change the way we Traverse<00:09:38.920> the<00:09:39.040> code<00:09:39.480> instead<00:09:39.839> of<00:09:40.519> uh<00:09:41.040> depth 00:09:41.310 --> 00:09:41.320 align:start position:0% Traverse the code instead of uh depth 00:09:41.320 --> 00:09:42.710 align:start position:0% Traverse the code instead of uh depth res<00:09:41.480> search<00:09:41.640> or<00:09:41.760> bread<00:09:41.959> for<00:09:42.079> search<00:09:42.279> reversal 00:09:42.710 --> 00:09:42.720 align:start position:0% res search or bread for search reversal 00:09:42.720 --> 00:09:44.910 align:start position:0% res search or bread for search reversal we<00:09:42.839> just<00:09:43.000> do<00:09:43.240> a<00:09:43.399> sequential<00:09:43.920> pass<00:09:44.200> through 00:09:44.910 --> 00:09:44.920 align:start position:0% we just do a sequential pass through 00:09:44.920 --> 00:09:47.110 align:start position:0% we just do a sequential pass through through<00:09:45.120> the<00:09:45.240> code<00:09:45.680> uh<00:09:45.800> front<00:09:46.120> to<00:09:46.320> back<00:09:46.800> just<00:09:46.959> a 00:09:47.110 --> 00:09:47.120 align:start position:0% through the code uh front to back just a 00:09:47.120 --> 00:09:48.949 align:start position:0% through the code uh front to back just a simple<00:09:47.360> Loop<00:09:47.680> we<00:09:47.760> do<00:09:47.920> not<00:09:48.040> follow<00:09:48.360> jumps<00:09:48.800> when 00:09:48.949 --> 00:09:48.959 align:start position:0% simple Loop we do not follow jumps when 00:09:48.959 --> 00:09:53.069 align:start position:0% simple Loop we do not follow jumps when they<00:09:49.079> see<00:09:49.360> them<00:09:50.320> instead<00:09:51.079> we<00:09:52.079> handle<00:09:52.680> jumps 00:09:53.069 --> 00:09:53.079 align:start position:0% they see them instead we handle jumps 00:09:53.079 --> 00:09:54.430 align:start position:0% they see them instead we handle jumps differently<00:09:53.560> depending<00:09:54.000> whether<00:09:54.200> it's<00:09:54.320> a 00:09:54.430 --> 00:09:54.440 align:start position:0% differently depending whether it's a 00:09:54.440 --> 00:09:56.790 align:start position:0% differently depending whether it's a forward<00:09:54.800> jump<00:09:55.079> or<00:09:55.279> backwards<00:09:55.760> jump<00:09:56.480> uh<00:09:56.600> so 00:09:56.790 --> 00:09:56.800 align:start position:0% forward jump or backwards jump uh so 00:09:56.800 --> 00:09:59.110 align:start position:0% forward jump or backwards jump uh so depending<00:09:57.120> on<00:09:57.320> its<00:09:57.880> relative<00:09:58.279> offset<00:09:58.880> and 00:09:59.110 --> 00:09:59.120 align:start position:0% depending on its relative offset and 00:09:59.120 --> 00:10:01.230 align:start position:0% depending on its relative offset and this<00:09:59.480> is<00:09:59.640> known<00:10:00.000> at<00:10:00.200> validation<00:10:00.640> time<00:10:00.880> because 00:10:01.230 --> 00:10:01.240 align:start position:0% this is known at validation time because 00:10:01.240 --> 00:10:04.269 align:start position:0% this is known at validation time because EF<00:10:01.720> has<00:10:02.519> static<00:10:02.839> jumps<00:10:03.279> instead<00:10:03.519> of<00:10:03.640> dynamic 00:10:04.269 --> 00:10:04.279 align:start position:0% EF has static jumps instead of dynamic 00:10:04.279 --> 00:10:07.190 align:start position:0% EF has static jumps instead of dynamic jumps<00:10:05.279> so<00:10:05.720> we<00:10:05.920> look<00:10:06.120> at<00:10:06.240> this<00:10:06.399> offset<00:10:06.920> if<00:10:07.079> it's 00:10:07.190 --> 00:10:07.200 align:start position:0% jumps so we look at this offset if it's 00:10:07.200 --> 00:10:09.949 align:start position:0% jumps so we look at this offset if it's a<00:10:07.360> forward<00:10:07.760> jump<00:10:08.760> we<00:10:08.959> always<00:10:09.240> allow<00:10:09.560> it<00:10:09.680> and<00:10:09.800> we 00:10:09.949 --> 00:10:09.959 align:start position:0% a forward jump we always allow it and we 00:10:09.959 --> 00:10:11.590 align:start position:0% a forward jump we always allow it and we just<00:10:10.120> record<00:10:10.560> the<00:10:10.720> stack<00:10:11.040> height<00:10:11.279> at<00:10:11.399> the 00:10:11.590 --> 00:10:11.600 align:start position:0% just record the stack height at the 00:10:11.600 --> 00:10:13.829 align:start position:0% just record the stack height at the Target<00:10:12.200> uh 00:10:13.829 --> 00:10:13.839 align:start position:0% Target uh 00:10:13.839 --> 00:10:16.069 align:start position:0% Target uh instruction<00:10:14.839> if<00:10:14.959> we<00:10:15.120> have<00:10:15.360> already<00:10:15.640> visited 00:10:16.069 --> 00:10:16.079 align:start position:0% instruction if we have already visited 00:10:16.079 --> 00:10:18.389 align:start position:0% instruction if we have already visited this<00:10:16.560> uh<00:10:16.680> or<00:10:16.839> we<00:10:17.000> have<00:10:17.240> already<00:10:17.480> seen<00:10:17.880> this 00:10:18.389 --> 00:10:18.399 align:start position:0% this uh or we have already seen this 00:10:18.399 --> 00:10:20.310 align:start position:0% this uh or we have already seen this target<00:10:18.720> instruction<00:10:19.200> before<00:10:19.560> we<00:10:19.800> expand<00:10:20.200> the 00:10:20.310 --> 00:10:20.320 align:start position:0% target instruction before we expand the 00:10:20.320 --> 00:10:22.750 align:start position:0% target instruction before we expand the stack<00:10:20.640> height<00:10:20.959> range<00:10:21.240> of<00:10:21.399> the 00:10:22.750 --> 00:10:22.760 align:start position:0% stack height range of the 00:10:22.760 --> 00:10:25.310 align:start position:0% stack height range of the Target<00:10:23.760> and<00:10:24.040> this<00:10:24.200> specifically<00:10:24.680> fixes<00:10:25.040> our 00:10:25.310 --> 00:10:25.320 align:start position:0% Target and this specifically fixes our 00:10:25.320 --> 00:10:27.829 align:start position:0% Target and this specifically fixes our problematic<00:10:25.880> case 00:10:27.829 --> 00:10:27.839 align:start position:0% problematic case 00:10:27.839 --> 00:10:30.389 align:start position:0% problematic case um<00:10:28.839> we<00:10:29.040> always<00:10:29.440> allow<00:10:29.760> this<00:10:29.880> jumps<00:10:30.160> into<00:10:30.320> a 00:10:30.389 --> 00:10:30.399 align:start position:0% um we always allow this jumps into a 00:10:30.399 --> 00:10:33.870 align:start position:0% um we always allow this jumps into a common<00:10:30.920> code<00:10:31.360> and<00:10:31.839> thanks<00:10:32.120> to<00:10:32.760> sequential<00:10:33.760> uh 00:10:33.870 --> 00:10:33.880 align:start position:0% common code and thanks to sequential uh 00:10:33.880 --> 00:10:36.629 align:start position:0% common code and thanks to sequential uh traversal<00:10:34.560> of<00:10:34.720> The<00:10:34.959> Code<00:10:35.959> by<00:10:36.120> the<00:10:36.279> time<00:10:36.440> we 00:10:36.629 --> 00:10:36.639 align:start position:0% traversal of The Code by the time we 00:10:36.639 --> 00:10:38.509 align:start position:0% traversal of The Code by the time we reach<00:10:37.079> the<00:10:37.320> validation<00:10:37.800> of<00:10:38.000> this<00:10:38.240> common 00:10:38.509 --> 00:10:38.519 align:start position:0% reach the validation of this common 00:10:38.519 --> 00:10:40.350 align:start position:0% reach the validation of this common helper<00:10:38.920> we<00:10:39.040> have<00:10:39.200> already<00:10:39.440> seen<00:10:39.760> all<00:10:39.920> forward 00:10:40.350 --> 00:10:40.360 align:start position:0% helper we have already seen all forward 00:10:40.360 --> 00:10:42.069 align:start position:0% helper we have already seen all forward jumps<00:10:40.680> into<00:10:40.920> it<00:10:41.040> so<00:10:41.200> we<00:10:41.320> have<00:10:41.440> seen<00:10:41.720> already 00:10:42.069 --> 00:10:42.079 align:start position:0% jumps into it so we have seen already 00:10:42.079 --> 00:10:44.829 align:start position:0% jumps into it so we have seen already all<00:10:42.519> stack<00:10:42.920> Heights<00:10:43.920> uh<00:10:44.000> at<00:10:44.160> all<00:10:44.279> of<00:10:44.399> the<00:10:44.519> jumps 00:10:44.829 --> 00:10:44.839 align:start position:0% all stack Heights uh at all of the jumps 00:10:44.839 --> 00:10:47.350 align:start position:0% all stack Heights uh at all of the jumps into<00:10:45.040> this<00:10:45.279> common<00:10:45.920> uh<00:10:46.279> uh<00:10:46.440> code<00:10:46.839> and<00:10:47.040> then<00:10:47.160> we 00:10:47.350 --> 00:10:47.360 align:start position:0% into this common uh uh code and then we 00:10:47.360 --> 00:10:49.590 align:start position:0% into this common uh uh code and then we validate<00:10:47.680> it<00:10:47.839> using<00:10:48.160> this<00:10:48.760> uh<00:10:49.120> stack<00:10:49.440> height 00:10:49.590 --> 00:10:49.600 align:start position:0% validate it using this uh stack height 00:10:49.600 --> 00:10:51.870 align:start position:0% validate it using this uh stack height range<00:10:49.880> that<00:10:50.000> we<00:10:50.079> have<00:10:50.480> observed<00:10:51.480> so<00:10:51.680> this 00:10:51.870 --> 00:10:51.880 align:start position:0% range that we have observed so this 00:10:51.880 --> 00:10:55.350 align:start position:0% range that we have observed so this fixes<00:10:52.519> the<00:10:52.800> problem<00:10:53.279> and<00:10:53.839> um<00:10:54.440> as<00:10:54.600> for<00:10:54.839> backward 00:10:55.350 --> 00:10:55.360 align:start position:0% fixes the problem and um as for backward 00:10:55.360 --> 00:10:57.990 align:start position:0% fixes the problem and um as for backward jumps<00:10:56.160> uh<00:10:56.320> we<00:10:56.519> still<00:10:56.839> keep<00:10:57.120> the<00:10:57.240> exactly<00:10:57.639> same 00:10:57.990 --> 00:10:58.000 align:start position:0% jumps uh we still keep the exactly same 00:10:58.000 --> 00:11:00.030 align:start position:0% jumps uh we still keep the exactly same restriction<00:10:58.480> as<00:10:58.639> before<00:10:58.959> we<00:10:59.320> require<00:10:59.760> equal 00:11:00.030 --> 00:11:00.040 align:start position:0% restriction as before we require equal 00:11:00.040 --> 00:11:01.990 align:start position:0% restriction as before we require equal stack<00:11:00.360> height<00:11:00.600> at<00:11:00.720> the<00:11:00.839> jump<00:11:01.320> instruction<00:11:01.839> and 00:11:01.990 --> 00:11:02.000 align:start position:0% stack height at the jump instruction and 00:11:02.000 --> 00:11:05.150 align:start position:0% stack height at the jump instruction and at<00:11:02.120> the<00:11:02.240> target<00:11:02.480> of<00:11:02.600> a<00:11:02.920> jump<00:11:03.920> this<00:11:04.079> means<00:11:04.760> that 00:11:05.150 --> 00:11:05.160 align:start position:0% at the target of a jump this means that 00:11:05.160 --> 00:11:06.829 align:start position:0% at the target of a jump this means that Loops<00:11:05.600> that<00:11:05.760> grow<00:11:05.959> or<00:11:06.079> Shrink<00:11:06.399> stack<00:11:06.680> are 00:11:06.829 --> 00:11:06.839 align:start position:0% Loops that grow or Shrink stack are 00:11:06.839 --> 00:11:08.230 align:start position:0% Loops that grow or Shrink stack are still<00:11:07.040> not<00:11:07.320> allowed<00:11:07.760> this<00:11:07.839> is<00:11:08.040> pretty 00:11:08.230 --> 00:11:08.240 align:start position:0% still not allowed this is pretty 00:11:08.240 --> 00:11:10.590 align:start position:0% still not allowed this is pretty reasonable<00:11:08.639> restriction<00:11:09.040> to<00:11:09.240> keep<00:11:09.639> no 00:11:10.590 --> 00:11:10.600 align:start position:0% reasonable restriction to keep no 00:11:10.600 --> 00:11:12.870 align:start position:0% reasonable restriction to keep no compilers<00:11:11.320> generate<00:11:11.760> such<00:11:11.959> Loops<00:11:12.360> anyway<00:11:12.800> and 00:11:12.870 --> 00:11:12.880 align:start position:0% compilers generate such Loops anyway and 00:11:12.880 --> 00:11:16.350 align:start position:0% compilers generate such Loops anyway and so<00:11:13.079> they<00:11:13.200> are<00:11:13.360> fine<00:11:13.560> with<00:11:14.160> it<00:11:15.160> uh<00:11:15.480> if<00:11:16.120> this 00:11:16.350 --> 00:11:16.360 align:start position:0% so they are fine with it uh if this 00:11:16.360 --> 00:11:19.030 align:start position:0% so they are fine with it uh if this backwards<00:11:16.920> jump<00:11:17.360> is<00:11:17.800> in<00:11:18.079> fact<00:11:18.279> a<00:11:18.480> jump<00:11:18.720> into<00:11:18.920> a 00:11:19.030 --> 00:11:19.040 align:start position:0% backwards jump is in fact a jump into a 00:11:19.040 --> 00:11:23.509 align:start position:0% backwards jump is in fact a jump into a helper<00:11:19.440> not<00:11:19.639> a<00:11:20.200> loop<00:11:21.200> uh<00:11:21.600> it<00:11:22.320> um<00:11:22.839> this<00:11:23.040> code 00:11:23.509 --> 00:11:23.519 align:start position:0% helper not a loop uh it um this code 00:11:23.519 --> 00:11:25.750 align:start position:0% helper not a loop uh it um this code always<00:11:23.839> can<00:11:24.000> be<00:11:24.200> reordered<00:11:24.800> in<00:11:24.880> a<00:11:25.040> way<00:11:25.279> that 00:11:25.750 --> 00:11:25.760 align:start position:0% always can be reordered in a way that 00:11:25.760 --> 00:11:27.829 align:start position:0% always can be reordered in a way that jumps<00:11:26.120> into<00:11:26.320> a<00:11:26.440> helper<00:11:26.760> is<00:11:26.880> a<00:11:27.000> forward<00:11:27.399> jump<00:11:27.720> so 00:11:27.829 --> 00:11:27.839 align:start position:0% jumps into a helper is a forward jump so 00:11:27.839 --> 00:11:29.750 align:start position:0% jumps into a helper is a forward jump so this<00:11:27.959> is<00:11:28.120> kind<00:11:28.240> of<00:11:28.320> an<00:11:28.480> implicit<00:11:28.880> require<00:11:29.440> M<00:11:29.600> to 00:11:29.750 --> 00:11:29.760 align:start position:0% this is kind of an implicit require M to 00:11:29.760 --> 00:11:31.550 align:start position:0% this is kind of an implicit require M to put<00:11:29.959> on<00:11:30.120> the<00:11:30.279> code<00:11:30.480> ordering<00:11:30.920> for<00:11:31.079> compilers 00:11:31.550 --> 00:11:31.560 align:start position:0% put on the code ordering for compilers 00:11:31.560 --> 00:11:35.190 align:start position:0% put on the code ordering for compilers to<00:11:32.440> and<00:11:32.800> this<00:11:32.920> is<00:11:33.200> always<00:11:33.600> can<00:11:33.760> be<00:11:33.920> done<00:11:34.279> and<00:11:34.959> so 00:11:35.190 --> 00:11:35.200 align:start position:0% to and this is always can be done and so 00:11:35.200 --> 00:11:37.069 align:start position:0% to and this is always can be done and so compilers<00:11:35.839> are<00:11:36.000> fine<00:11:36.240> with 00:11:37.069 --> 00:11:37.079 align:start position:0% compilers are fine with 00:11:37.079 --> 00:11:39.550 align:start position:0% compilers are fine with this<00:11:38.079> if<00:11:38.200> we<00:11:38.320> see<00:11:38.519> a<00:11:38.800> regular<00:11:39.160> instruction 00:11:39.550 --> 00:11:39.560 align:start position:0% this if we see a regular instruction 00:11:39.560 --> 00:11:41.590 align:start position:0% this if we see a regular instruction which<00:11:39.680> is<00:11:39.800> not<00:11:39.920> a<00:11:40.040> jump<00:11:40.360> we<00:11:40.600> just<00:11:40.880> modify<00:11:41.399> both 00:11:41.590 --> 00:11:41.600 align:start position:0% which is not a jump we just modify both 00:11:41.600 --> 00:11:42.829 align:start position:0% which is not a jump we just modify both ends<00:11:41.800> of<00:11:41.920> the<00:11:42.040> stack<00:11:42.279> height<00:11:42.440> range<00:11:42.720> both 00:11:42.829 --> 00:11:42.839 align:start position:0% ends of the stack height range both 00:11:42.839 --> 00:11:43.949 align:start position:0% ends of the stack height range both minimum<00:11:43.160> and 00:11:43.949 --> 00:11:43.959 align:start position:0% minimum and 00:11:43.959 --> 00:11:46.670 align:start position:0% minimum and maximum<00:11:44.959> uh<00:11:45.120> stack<00:11:45.440> underflow<00:11:46.040> is<00:11:46.200> checked 00:11:46.670 --> 00:11:46.680 align:start position:0% maximum uh stack underflow is checked 00:11:46.680 --> 00:11:49.670 align:start position:0% maximum uh stack underflow is checked obviously<00:11:47.079> using<00:11:47.440> minimum<00:11:47.839> end<00:11:48.040> of<00:11:48.160> the<00:11:48.680> range 00:11:49.670 --> 00:11:49.680 align:start position:0% obviously using minimum end of the range 00:11:49.680 --> 00:11:52.069 align:start position:0% obviously using minimum end of the range and<00:11:50.040> one<00:11:50.320> extra<00:11:50.720> restriction<00:11:51.240> on<00:11:51.600> or<00:11:51.760> one 00:11:52.069 --> 00:11:52.079 align:start position:0% and one extra restriction on or one 00:11:52.079 --> 00:11:54.710 align:start position:0% and one extra restriction on or one change<00:11:52.440> in<00:11:52.680> how<00:11:52.839> we<00:11:53.000> Define<00:11:53.360> unreachable<00:11:53.920> code 00:11:54.710 --> 00:11:54.720 align:start position:0% change in how we Define unreachable code 00:11:54.720 --> 00:11:57.389 align:start position:0% change in how we Define unreachable code this<00:11:54.839> is<00:11:55.040> very<00:11:55.240> much<00:11:55.680> related<00:11:56.200> to<00:11:56.880> backwards 00:11:57.389 --> 00:11:57.399 align:start position:0% this is very much related to backwards 00:11:57.399 --> 00:11:59.230 align:start position:0% this is very much related to backwards jump<00:11:57.800> rule<00:11:58.120> that<00:11:58.240> I<00:11:58.320> have<00:11:58.480> already<00:11:58.920> mentioned 00:11:59.230 --> 00:11:59.240 align:start position:0% jump rule that I have already mentioned 00:11:59.240 --> 00:12:02.790 align:start position:0% jump rule that I have already mentioned mentioned<00:11:59.639> just<00:11:59.839> now<00:12:00.800> so<00:12:01.040> we<00:12:01.279> also<00:12:02.160> uh<00:12:02.440> expand 00:12:02.790 --> 00:12:02.800 align:start position:0% mentioned just now so we also uh expand 00:12:02.800 --> 00:12:04.110 align:start position:0% mentioned just now so we also uh expand a<00:12:02.920> bit<00:12:03.079> the<00:12:03.200> definition<00:12:03.560> of<00:12:03.720> what<00:12:03.839> is<00:12:03.959> UN 00:12:04.110 --> 00:12:04.120 align:start position:0% a bit the definition of what is UN 00:12:04.120 --> 00:12:06.110 align:start position:0% a bit the definition of what is UN reachable<00:12:04.440> code<00:12:04.720> if<00:12:04.839> some<00:12:05.079> code<00:12:05.360> is<00:12:05.519> reachable 00:12:06.110 --> 00:12:06.120 align:start position:0% reachable code if some code is reachable 00:12:06.120 --> 00:12:08.230 align:start position:0% reachable code if some code is reachable only<00:12:06.519> via<00:12:06.760> a<00:12:06.880> backwards<00:12:07.360> jump<00:12:07.760> we<00:12:07.959> also 00:12:08.230 --> 00:12:08.240 align:start position:0% only via a backwards jump we also 00:12:08.240 --> 00:12:10.190 align:start position:0% only via a backwards jump we also consider<00:12:08.560> it<00:12:08.680> unreachable<00:12:09.320> now<00:12:09.920> this<00:12:10.040> is 00:12:10.190 --> 00:12:10.200 align:start position:0% consider it unreachable now this is 00:12:10.200 --> 00:12:13.470 align:start position:0% consider it unreachable now this is needed<00:12:10.519> to<00:12:10.760> make<00:12:11.120> this<00:12:11.399> sequential<00:12:11.920> traversal 00:12:13.470 --> 00:12:13.480 align:start position:0% needed to make this sequential traversal 00:12:13.480 --> 00:12:16.710 align:start position:0% needed to make this sequential traversal possible<00:12:14.480> and<00:12:14.680> this<00:12:14.760> is<00:12:14.920> all<00:12:15.360> also<00:12:15.760> always<00:12:16.560> uh 00:12:16.710 --> 00:12:16.720 align:start position:0% possible and this is all also always uh 00:12:16.720 --> 00:12:19.310 align:start position:0% possible and this is all also always uh achievable<00:12:17.240> by<00:12:17.399> compilers<00:12:18.279> they<00:12:18.600> need<00:12:18.839> to<00:12:19.079> do 00:12:19.310 --> 00:12:19.320 align:start position:0% achievable by compilers they need to do 00:12:19.320 --> 00:12:21.150 align:start position:0% achievable by compilers they need to do some<00:12:19.560> kind<00:12:19.720> of<00:12:20.040> topological<00:12:20.519> sort<00:12:20.800> ordering 00:12:21.150 --> 00:12:21.160 align:start position:0% some kind of topological sort ordering 00:12:21.160 --> 00:12:24.310 align:start position:0% some kind of topological sort ordering of<00:12:21.360> the<00:12:21.839> basic<00:12:22.120> blocks<00:12:22.440> in<00:12:22.560> the<00:12:22.720> code<00:12:23.519> uh<00:12:23.800> and 00:12:24.310 --> 00:12:24.320 align:start position:0% of the basic blocks in the code uh and 00:12:24.320 --> 00:12:27.949 align:start position:0% of the basic blocks in the code uh and uh<00:12:24.800> it<00:12:24.959> always<00:12:25.199> can<00:12:25.360> be<00:12:25.839> done<00:12:26.839> uh<00:12:27.000> so<00:12:27.680> this 00:12:27.949 --> 00:12:27.959 align:start position:0% uh it always can be done uh so this 00:12:27.959 --> 00:12:30.189 align:start position:0% uh it always can be done uh so this restriction<00:12:28.399> is<00:12:28.519> fine<00:12:28.760> some<00:12:28.920> other<00:12:29.440> uh<00:12:29.720> VMS 00:12:30.189 --> 00:12:30.199 align:start position:0% restriction is fine some other uh VMS 00:12:30.199 --> 00:12:31.590 align:start position:0% restriction is fine some other uh VMS also<00:12:30.440> have<00:12:30.680> similar 00:12:31.590 --> 00:12:31.600 align:start position:0% also have similar 00:12:31.600 --> 00:12:36.470 align:start position:0% also have similar Rule<00:12:32.600> and<00:12:33.320> um<00:12:34.320> also<00:12:34.720> because<00:12:35.720> we<00:12:35.880> have<00:12:36.160> this 00:12:36.470 --> 00:12:36.480 align:start position:0% Rule and um also because we have this 00:12:36.480 --> 00:12:38.629 align:start position:0% Rule and um also because we have this simple<00:12:37.160> Loop<00:12:37.399> over<00:12:37.639> all<00:12:37.880> instructions<00:12:38.440> every 00:12:38.629 --> 00:12:38.639 align:start position:0% simple Loop over all instructions every 00:12:38.639 --> 00:12:40.269 align:start position:0% simple Loop over all instructions every instruction<00:12:39.000> is<00:12:39.160> visited<00:12:39.560> exactly<00:12:39.880> once<00:12:40.120> so 00:12:40.269 --> 00:12:40.279 align:start position:0% instruction is visited exactly once so 00:12:40.279 --> 00:12:41.790 align:start position:0% instruction is visited exactly once so we<00:12:40.360> are<00:12:40.519> still<00:12:40.720> fine<00:12:41.040> complexity<00:12:41.560> wise 00:12:41.790 --> 00:12:41.800 align:start position:0% we are still fine complexity wise 00:12:41.800 --> 00:12:43.189 align:start position:0% we are still fine complexity wise complexity<00:12:42.240> is<00:12:42.360> still 00:12:43.189 --> 00:12:43.199 align:start position:0% complexity is still 00:12:43.199 --> 00:12:45.389 align:start position:0% complexity is still linear<00:12:44.199> I'll<00:12:44.360> show<00:12:44.560> an<00:12:44.720> example<00:12:45.000> how<00:12:45.240> this 00:12:45.389 --> 00:12:45.399 align:start position:0% linear I'll show an example how this 00:12:45.399 --> 00:12:48.550 align:start position:0% linear I'll show an example how this would<00:12:45.600> work<00:12:46.160> now<00:12:47.160> uh<00:12:47.279> so<00:12:47.480> we'll<00:12:47.680> need<00:12:47.959> an<00:12:48.120> array 00:12:48.550 --> 00:12:48.560 align:start position:0% would work now uh so we'll need an array 00:12:48.560 --> 00:12:50.230 align:start position:0% would work now uh so we'll need an array of<00:12:48.760> two<00:12:48.959> arrays<00:12:49.320> of<00:12:49.480> minimum<00:12:49.800> and<00:12:49.920> maximum 00:12:50.230 --> 00:12:50.240 align:start position:0% of two arrays of minimum and maximum 00:12:50.240 --> 00:12:51.990 align:start position:0% of two arrays of minimum and maximum stack<00:12:50.560> height<00:12:50.760> or<00:12:50.920> array<00:12:51.199> of 00:12:51.990 --> 00:12:52.000 align:start position:0% stack height or array of 00:12:52.000 --> 00:12:54.509 align:start position:0% stack height or array of pairs<00:12:53.000> uh<00:12:53.240> note<00:12:53.519> that<00:12:53.680> we<00:12:53.760> do<00:12:53.880> not<00:12:54.000> need<00:12:54.160> a<00:12:54.279> work 00:12:54.509 --> 00:12:54.519 align:start position:0% pairs uh note that we do not need a work 00:12:54.519 --> 00:12:55.910 align:start position:0% pairs uh note that we do not need a work list<00:12:54.760> here<00:12:55.000> because<00:12:55.199> it's<00:12:55.360> just<00:12:55.480> a<00:12:55.639> simple 00:12:55.910 --> 00:12:55.920 align:start position:0% list here because it's just a simple 00:12:55.920 --> 00:12:58.470 align:start position:0% list here because it's just a simple Loop<00:12:56.560> uh<00:12:56.680> over<00:12:56.959> instructions<00:12:57.760> so<00:12:57.959> we<00:12:58.120> start 00:12:58.470 --> 00:12:58.480 align:start position:0% Loop uh over instructions so we start 00:12:58.480 --> 00:13:01.150 align:start position:0% Loop uh over instructions so we start with<00:12:58.600> the<00:12:58.760> first<00:12:58.959> one<00:12:59.440> push<00:13:00.320> uh<00:13:00.639> is<00:13:00.760> a<00:13:00.920> simple 00:13:01.150 --> 00:13:01.160 align:start position:0% with the first one push uh is a simple 00:13:01.160 --> 00:13:02.990 align:start position:0% with the first one push uh is a simple instruction<00:13:01.560> that<00:13:01.720> modifies<00:13:02.279> both<00:13:02.680> minimum 00:13:02.990 --> 00:13:03.000 align:start position:0% instruction that modifies both minimum 00:13:03.000 --> 00:13:06.590 align:start position:0% instruction that modifies both minimum and<00:13:03.160> maximum<00:13:03.519> so<00:13:03.720> 0<00:13:04.120> to0<00:13:04.680> becomes<00:13:05.199> 0<00:13:05.600> 1<00:13:05.760> to<00:13:05.920> one 00:13:06.590 --> 00:13:06.600 align:start position:0% and maximum so 0 to0 becomes 0 1 to one 00:13:06.600 --> 00:13:08.870 align:start position:0% and maximum so 0 to0 becomes 0 1 to one call<00:13:06.839> data<00:13:07.040> Lo<00:13:07.199> doesn't<00:13:07.440> change<00:13:07.680> it<00:13:08.279> then<00:13:08.519> this 00:13:08.870 --> 00:13:08.880 align:start position:0% call data Lo doesn't change it then this 00:13:08.880 --> 00:13:11.189 align:start position:0% call data Lo doesn't change it then this conditional<00:13:09.199> jump<00:13:10.199> uh<00:13:10.320> it<00:13:10.399> is<00:13:10.480> a<00:13:10.600> forward<00:13:10.959> jump 00:13:11.189 --> 00:13:11.199 align:start position:0% conditional jump uh it is a forward jump 00:13:11.199 --> 00:13:13.269 align:start position:0% conditional jump uh it is a forward jump so<00:13:11.320> it<00:13:11.440> is<00:13:11.519> a<00:13:11.639> load<00:13:12.199> and<00:13:12.399> we<00:13:12.560> have<00:13:12.920> just<00:13:13.079> to 00:13:13.269 --> 00:13:13.279 align:start position:0% so it is a load and we have just to 00:13:13.279 --> 00:13:15.470 align:start position:0% so it is a load and we have just to record<00:13:13.639> the<00:13:13.760> stack<00:13:14.079> height<00:13:14.440> at<00:13:14.560> the<00:13:14.800> Target<00:13:15.279> it 00:13:15.470 --> 00:13:15.480 align:start position:0% record the stack height at the Target it 00:13:15.480 --> 00:13:18.389 align:start position:0% record the stack height at the Target it is<00:13:15.880> zero<00:13:16.199> after<00:13:16.440> or<00:13:16.880> Pi<00:13:17.079> so<00:13:17.240> we<00:13:17.519> record<00:13:17.880> 0<00:13:18.199> to 00:13:18.389 --> 00:13:18.399 align:start position:0% is zero after or Pi so we record 0 to 00:13:18.399 --> 00:13:21.069 align:start position:0% is zero after or Pi so we record 0 to zero<00:13:18.720> at<00:13:18.959> offset 00:13:21.069 --> 00:13:21.079 align:start position:0% zero at offset 00:13:21.079 --> 00:13:25.030 align:start position:0% zero at offset X<00:13:22.120> um<00:13:23.120> uh<00:13:23.480> then<00:13:23.600> we<00:13:23.760> continue<00:13:24.120> with<00:13:24.240> the<00:13:24.760> next 00:13:25.030 --> 00:13:25.040 align:start position:0% X um uh then we continue with the next 00:13:25.040 --> 00:13:27.790 align:start position:0% X um uh then we continue with the next instruction<00:13:25.920> this<00:13:26.079> is<00:13:26.680> yeah<00:13:26.839> another<00:13:27.519> push 00:13:27.790 --> 00:13:27.800 align:start position:0% instruction this is yeah another push 00:13:27.800 --> 00:13:30.710 align:start position:0% instruction this is yeah another push and<00:13:28.079> push<00:13:28.480> and<00:13:28.760> C<00:13:29.240> Lo<00:13:29.560> and<00:13:30.000> then<00:13:30.240> another 00:13:30.710 --> 00:13:30.720 align:start position:0% and push and C Lo and then another 00:13:30.720 --> 00:13:33.389 align:start position:0% and push and C Lo and then another conditional<00:13:31.000> jump<00:13:31.279> that<00:13:31.440> targets<00:13:32.040> the<00:13:32.399> same 00:13:33.389 --> 00:13:33.399 align:start position:0% conditional jump that targets the same 00:13:33.399 --> 00:13:35.269 align:start position:0% conditional jump that targets the same offset<00:13:33.760> that<00:13:33.880> we<00:13:34.000> have<00:13:34.160> already<00:13:34.440> seen<00:13:34.800> before 00:13:35.269 --> 00:13:35.279 align:start position:0% offset that we have already seen before 00:13:35.279 --> 00:13:37.629 align:start position:0% offset that we have already seen before at<00:13:35.480> this<00:13:35.720> point<00:13:36.440> uh<00:13:36.600> stack<00:13:36.959> height<00:13:37.199> is<00:13:37.360> one 00:13:37.629 --> 00:13:37.639 align:start position:0% at this point uh stack height is one 00:13:37.639 --> 00:13:40.790 align:start position:0% at this point uh stack height is one after<00:13:37.880> R<00:13:38.079> jum<00:13:38.399> pi<00:13:39.240> and<00:13:39.440> we<00:13:39.720> have<00:13:39.920> to<00:13:40.480> at<00:13:40.639> this 00:13:40.790 --> 00:13:40.800 align:start position:0% after R jum pi and we have to at this 00:13:40.800 --> 00:13:42.590 align:start position:0% after R jum pi and we have to at this point<00:13:41.160> expand<00:13:41.560> the<00:13:41.720> stack<00:13:41.959> height<00:13:42.160> range<00:13:42.440> that 00:13:42.590 --> 00:13:42.600 align:start position:0% point expand the stack height range that 00:13:42.600 --> 00:13:44.949 align:start position:0% point expand the stack height range that we<00:13:42.720> have<00:13:42.880> seen<00:13:43.440> at<00:13:43.560> the<00:13:43.720> Target<00:13:44.079> before<00:13:44.320> so<00:13:44.440> 0<00:13:44.720> 0 00:13:44.949 --> 00:13:44.959 align:start position:0% we have seen at the Target before so 0 0 00:13:44.959 --> 00:13:47.629 align:start position:0% we have seen at the Target before so 0 0 becomes<00:13:45.360> 01<00:13:46.360> then<00:13:46.519> we<00:13:46.680> have<00:13:46.800> a<00:13:47.000> stop<00:13:47.360> with<00:13:47.480> an 00:13:47.629 --> 00:13:47.639 align:start position:0% becomes 01 then we have a stop with an 00:13:47.639 --> 00:13:50.230 align:start position:0% becomes 01 then we have a stop with an extra<00:13:48.040> value<00:13:49.040> on<00:13:49.160> the<00:13:49.320> stack<00:13:49.600> this<00:13:49.680> is<00:13:49.800> allowed 00:13:50.230 --> 00:13:50.240 align:start position:0% extra value on the stack this is allowed 00:13:50.240 --> 00:13:52.189 align:start position:0% extra value on the stack this is allowed and<00:13:50.480> valid<00:13:50.839> and<00:13:50.959> then<00:13:51.079> we<00:13:51.240> get<00:13:51.399> to<00:13:51.600> this<00:13:51.759> Branch 00:13:52.189 --> 00:13:52.199 align:start position:0% and valid and then we get to this Branch 00:13:52.199 --> 00:13:53.990 align:start position:0% and valid and then we get to this Branch this<00:13:52.320> is<00:13:52.800> interesting<00:13:53.320> Branch<00:13:53.639> because<00:13:53.839> it 00:13:53.990 --> 00:13:54.000 align:start position:0% this is interesting Branch because it 00:13:54.000 --> 00:13:55.749 align:start position:0% this is interesting Branch because it has<00:13:54.279> multiple<00:13:54.720> possible<00:13:55.000> St<00:13:55.320> Heights<00:13:55.519> it<00:13:55.639> can 00:13:55.749 --> 00:13:55.759 align:start position:0% has multiple possible St Heights it can 00:13:55.759 --> 00:13:58.110 align:start position:0% has multiple possible St Heights it can be<00:13:55.920> either<00:13:56.160> zero<00:13:56.399> or<00:13:56.600> one<00:13:56.920> here<00:13:57.560> then<00:13:57.800> push 00:13:58.110 --> 00:13:58.120 align:start position:0% be either zero or one here then push 00:13:58.120 --> 00:13:59.910 align:start position:0% be either zero or one here then push would<00:13:58.320> modify<00:13:58.680> both<00:13:59.079> minimum<00:13:59.320> and<00:13:59.440> maximum<00:13:59.800> so 00:13:59.910 --> 00:13:59.920 align:start position:0% would modify both minimum and maximum so 00:13:59.920 --> 00:14:02.790 align:start position:0% would modify both minimum and maximum so it<00:14:00.000> shifts<00:14:00.600> the<00:14:00.800> St<00:14:01.120> height<00:14:01.320> range<00:14:02.040> 01<00:14:02.519> becomes 00:14:02.790 --> 00:14:02.800 align:start position:0% it shifts the St height range 01 becomes 00:14:02.800 --> 00:14:04.990 align:start position:0% it shifts the St height range 01 becomes one<00:14:03.000> two<00:14:03.320> and<00:14:03.519> another<00:14:03.839> push<00:14:04.360> and<00:14:04.519> revert 00:14:04.990 --> 00:14:05.000 align:start position:0% one two and another push and revert 00:14:05.000 --> 00:14:06.590 align:start position:0% one two and another push and revert checks<00:14:05.279> for<00:14:05.560> possible 00:14:06.590 --> 00:14:06.600 align:start position:0% checks for possible 00:14:06.600 --> 00:14:11.430 align:start position:0% checks for possible underflow<00:14:07.600> uh<00:14:08.680> uh<00:14:09.680> using<00:14:10.079> minimum<00:14:10.800> and<00:14:10.959> two<00:14:11.240> is 00:14:11.430 --> 00:14:11.440 align:start position:0% underflow uh uh using minimum and two is 00:14:11.440 --> 00:14:12.829 align:start position:0% underflow uh uh using minimum and two is exactly<00:14:11.720> what<00:14:11.880> revert<00:14:12.199> needs<00:14:12.480> so<00:14:12.680> no 00:14:12.829 --> 00:14:12.839 align:start position:0% exactly what revert needs so no 00:14:12.839 --> 00:14:14.550 align:start position:0% exactly what revert needs so no underflow<00:14:13.279> happens<00:14:13.639> this<00:14:13.759> code<00:14:14.000> is<00:14:14.199> valid<00:14:14.480> in 00:14:14.550 --> 00:14:14.560 align:start position:0% underflow happens this code is valid in 00:14:14.560 --> 00:14:17.230 align:start position:0% underflow happens this code is valid in the<00:14:14.680> end<00:14:14.920> this<00:14:15.120> concludes<00:14:15.560> the<00:14:16.079> validation<00:14:17.079> uh 00:14:17.230 --> 00:14:17.240 align:start position:0% the end this concludes the validation uh 00:14:17.240 --> 00:14:18.910 align:start position:0% the end this concludes the validation uh note<00:14:17.480> that<00:14:17.639> this<00:14:17.759> code<00:14:18.040> is<00:14:18.199> very<00:14:18.360> similar<00:14:18.720> to 00:14:18.910 --> 00:14:18.920 align:start position:0% note that this code is very similar to 00:14:18.920 --> 00:14:20.870 align:start position:0% note that this code is very similar to the<00:14:19.079> problematic<00:14:19.639> case<00:14:20.199> uh<00:14:20.279> that<00:14:20.399> I<00:14:20.480> showed<00:14:20.759> a 00:14:20.870 --> 00:14:20.880 align:start position:0% the problematic case uh that I showed a 00:14:20.880 --> 00:14:23.110 align:start position:0% the problematic case uh that I showed a couple<00:14:21.079> of<00:14:21.160> slides<00:14:21.519> before<00:14:22.320> this<00:14:22.440> is<00:14:22.680> like<00:14:22.839> a 00:14:23.110 --> 00:14:23.120 align:start position:0% couple of slides before this is like a 00:14:23.120 --> 00:14:25.030 align:start position:0% couple of slides before this is like a common<00:14:23.600> helper<00:14:24.040> that<00:14:24.160> reverts<00:14:24.560> and<00:14:24.720> a<00:14:24.839> couple 00:14:25.030 --> 00:14:25.040 align:start position:0% common helper that reverts and a couple 00:14:25.040 --> 00:14:26.509 align:start position:0% common helper that reverts and a couple of<00:14:25.160> jumps<00:14:25.560> from<00:14:25.759> different<00:14:26.000> stack<00:14:26.279> Heights 00:14:26.509 --> 00:14:26.519 align:start position:0% of jumps from different stack Heights 00:14:26.519 --> 00:14:27.269 align:start position:0% of jumps from different stack Heights into 00:14:27.269 --> 00:14:27.279 align:start position:0% into 00:14:27.279 --> 00:14:30.189 align:start position:0% into it<00:14:28.279> uh<00:14:28.399> so<00:14:28.600> given<00:14:28.800> this<00:14:29.120> algorithm<00:14:30.040> uh 00:14:30.189 --> 00:14:30.199 align:start position:0% it uh so given this algorithm uh 00:14:30.199 --> 00:14:32.629 align:start position:0% it uh so given this algorithm uh concludes<00:14:31.120> successfully<00:14:32.120> uh<00:14:32.320> we<00:14:32.440> are 00:14:32.629 --> 00:14:32.639 align:start position:0% concludes successfully uh we are 00:14:32.639 --> 00:14:34.670 align:start position:0% concludes successfully uh we are guaranteed<00:14:33.160> that<00:14:33.279> no<00:14:33.440> underflows<00:14:34.199> happen<00:14:34.519> at 00:14:34.670 --> 00:14:34.680 align:start position:0% guaranteed that no underflows happen at 00:14:34.680 --> 00:14:37.790 align:start position:0% guaranteed that no underflows happen at run<00:14:35.079> time<00:14:35.720> uh<00:14:35.880> ever<00:14:36.240> at<00:14:36.360> all<00:14:37.040> uh<00:14:37.279> and<00:14:37.440> we<00:14:37.560> can 00:14:37.790 --> 00:14:37.800 align:start position:0% run time uh ever at all uh and we can 00:14:37.800 --> 00:14:39.269 align:start position:0% run time uh ever at all uh and we can completely<00:14:38.240> Amit<00:14:38.639> them<00:14:38.959> from<00:14:39.160> the 00:14:39.269 --> 00:14:39.279 align:start position:0% completely Amit them from the 00:14:39.279 --> 00:14:41.590 align:start position:0% completely Amit them from the interpreted<00:14:39.800> Loop<00:14:40.800> this<00:14:40.880> is<00:14:41.040> not<00:14:41.240> the<00:14:41.399> case 00:14:41.590 --> 00:14:41.600 align:start position:0% interpreted Loop this is not the case 00:14:41.600 --> 00:14:43.910 align:start position:0% interpreted Loop this is not the case with<00:14:41.759> overflow<00:14:42.399> checks<00:14:42.959> uh<00:14:43.040> we<00:14:43.160> cannot<00:14:43.560> remove 00:14:43.910 --> 00:14:43.920 align:start position:0% with overflow checks uh we cannot remove 00:14:43.920 --> 00:14:46.710 align:start position:0% with overflow checks uh we cannot remove them<00:14:44.399> uh<00:14:44.720> completely<00:14:45.720> but<00:14:45.920> we<00:14:46.040> can<00:14:46.240> minimize 00:14:46.710 --> 00:14:46.720 align:start position:0% them uh completely but we can minimize 00:14:46.720 --> 00:14:48.670 align:start position:0% them uh completely but we can minimize how<00:14:46.920> often<00:14:47.160> we<00:14:47.320> do<00:14:47.480> them<00:14:47.639> and<00:14:47.800> not<00:14:48.040> do<00:14:48.240> them<00:14:48.440> for 00:14:48.670 --> 00:14:48.680 align:start position:0% how often we do them and not do them for 00:14:48.680 --> 00:14:51.990 align:start position:0% how often we do them and not do them for every<00:14:49.240> instruction<00:14:50.240> as<00:14:50.440> current<00:14:50.720> evm 00:14:51.990 --> 00:14:52.000 align:start position:0% every instruction as current evm 00:14:52.000 --> 00:14:57.629 align:start position:0% every instruction as current evm does<00:14:53.000> uh<00:14:53.240> so<00:14:53.639> to<00:14:53.839> make<00:14:54.759> this<00:14:55.759> uh<00:14:56.600> work<00:14:57.000> we<00:14:57.199> start 00:14:57.629 --> 00:14:57.639 align:start position:0% does uh so to make this uh work we start 00:14:57.639 --> 00:15:01.189 align:start position:0% does uh so to make this uh work we start with<00:14:58.040> the<00:14:58.560> with<00:14:58.759> what<00:14:59.399> previous<00:15:00.199> underflows 00:15:01.189 --> 00:15:01.199 align:start position:0% with the with what previous underflows 00:15:01.199 --> 00:15:03.269 align:start position:0% with the with what previous underflows uh<00:15:01.480> validation<00:15:01.959> algorithm<00:15:02.440> gave<00:15:02.600> us<00:15:03.120> we 00:15:03.269 --> 00:15:03.279 align:start position:0% uh validation algorithm gave us we 00:15:03.279 --> 00:15:04.550 align:start position:0% uh validation algorithm gave us we recorded<00:15:03.759> stack<00:15:04.040> height<00:15:04.240> at<00:15:04.320> every 00:15:04.550 --> 00:15:04.560 align:start position:0% recorded stack height at every 00:15:04.560 --> 00:15:06.470 align:start position:0% recorded stack height at every instruction<00:15:05.079> in<00:15:05.279> this<00:15:05.440> algorithm<00:15:06.040> and<00:15:06.160> we<00:15:06.279> can 00:15:06.470 --> 00:15:06.480 align:start position:0% instruction in this algorithm and we can 00:15:06.480 --> 00:15:08.670 align:start position:0% instruction in this algorithm and we can just<00:15:07.000> find<00:15:07.360> maximum<00:15:07.800> of<00:15:07.959> these<00:15:08.120> stack<00:15:08.399> Heights 00:15:08.670 --> 00:15:08.680 align:start position:0% just find maximum of these stack Heights 00:15:08.680 --> 00:15:11.230 align:start position:0% just find maximum of these stack Heights and<00:15:08.880> this<00:15:09.160> value<00:15:09.560> value<00:15:09.880> is<00:15:10.040> going<00:15:10.240> to<00:15:10.399> mean 00:15:11.230 --> 00:15:11.240 align:start position:0% and this value value is going to mean 00:15:11.240 --> 00:15:13.189 align:start position:0% and this value value is going to mean maximum<00:15:11.680> stack<00:15:12.000> height<00:15:12.320> value<00:15:12.720> of<00:15:13.000> this 00:15:13.189 --> 00:15:13.199 align:start position:0% maximum stack height value of this 00:15:13.199 --> 00:15:16.030 align:start position:0% maximum stack height value of this functions<00:15:14.120> frame<00:15:15.120> if<00:15:15.279> this<00:15:15.440> value<00:15:15.680> is<00:15:15.800> above 00:15:16.030 --> 00:15:16.040 align:start position:0% functions frame if this value is above 00:15:16.040 --> 00:15:17.990 align:start position:0% functions frame if this value is above stack<00:15:16.279> height<00:15:16.480> limit<00:15:16.759> it<00:15:16.880> means<00:15:17.440> execution<00:15:17.839> of 00:15:17.990 --> 00:15:18.000 align:start position:0% stack height limit it means execution of 00:15:18.000 --> 00:15:19.910 align:start position:0% stack height limit it means execution of this<00:15:18.160> function<00:15:18.519> May<00:15:18.800> overflow<00:15:19.279> and<00:15:19.440> we<00:15:19.600> reject 00:15:19.910 --> 00:15:19.920 align:start position:0% this function May overflow and we reject 00:15:19.920 --> 00:15:21.470 align:start position:0% this function May overflow and we reject it<00:15:20.079> immediately<00:15:20.519> at<00:15:20.680> validation<00:15:21.079> we<00:15:21.199> do<00:15:21.320> not 00:15:21.470 --> 00:15:21.480 align:start position:0% it immediately at validation we do not 00:15:21.480 --> 00:15:24.230 align:start position:0% it immediately at validation we do not allow<00:15:21.720> it<00:15:21.920> to<00:15:22.040> be<00:15:22.639> deployed<00:15:23.639> uh<00:15:23.759> if<00:15:23.920> it<00:15:24.079> is 00:15:24.230 --> 00:15:24.240 align:start position:0% allow it to be deployed uh if it is 00:15:24.240 --> 00:15:25.910 align:start position:0% allow it to be deployed uh if it is within<00:15:24.480> the<00:15:24.600> limit<00:15:24.839> we<00:15:25.040> record<00:15:25.399> this<00:15:25.560> maximum 00:15:25.910 --> 00:15:25.920 align:start position:0% within the limit we record this maximum 00:15:25.920 --> 00:15:28.269 align:start position:0% within the limit we record this maximum stack<00:15:26.160> height<00:15:26.399> value<00:15:26.759> in<00:15:27.040> this<00:15:27.759> functions 00:15:28.269 --> 00:15:28.279 align:start position:0% stack height value in this functions 00:15:28.279 --> 00:15:30.389 align:start position:0% stack height value in this functions metadata<00:15:29.079> the<00:15:29.160> EF<00:15:29.519> header<00:15:29.920> and<00:15:30.079> then<00:15:30.240> this 00:15:30.389 --> 00:15:30.399 align:start position:0% metadata the EF header and then this 00:15:30.399 --> 00:15:32.309 align:start position:0% metadata the EF header and then this value<00:15:30.639> is<00:15:30.759> used<00:15:30.959> for<00:15:31.199> validating<00:15:31.680> the<00:15:31.839> calls 00:15:32.309 --> 00:15:32.319 align:start position:0% value is used for validating the calls 00:15:32.319 --> 00:15:35.430 align:start position:0% value is used for validating the calls into<00:15:32.600> this<00:15:33.120> section<00:15:34.120> and<00:15:34.360> also<00:15:34.680> at<00:15:34.920> execution 00:15:35.430 --> 00:15:35.440 align:start position:0% into this section and also at execution 00:15:35.440 --> 00:15:37.470 align:start position:0% into this section and also at execution time<00:15:35.639> when<00:15:35.759> we<00:15:35.920> execute<00:15:36.399> call<00:15:36.639> F<00:15:36.839> for<00:15:37.000> jump<00:15:37.240> F 00:15:37.470 --> 00:15:37.480 align:start position:0% time when we execute call F for jump F 00:15:37.480 --> 00:15:40.590 align:start position:0% time when we execute call F for jump F into<00:15:37.800> this<00:15:38.319> uh<00:15:38.560> function<00:15:39.040> so<00:15:40.000> in<00:15:40.120> the<00:15:40.240> end<00:15:40.440> we 00:15:40.590 --> 00:15:40.600 align:start position:0% into this uh function so in the end we 00:15:40.600 --> 00:15:42.910 align:start position:0% into this uh function so in the end we only<00:15:41.000> have<00:15:41.120> to<00:15:41.319> do<00:15:41.600> runtime<00:15:42.040> overflow<00:15:42.519> checks 00:15:42.910 --> 00:15:42.920 align:start position:0% only have to do runtime overflow checks 00:15:42.920 --> 00:15:46.389 align:start position:0% only have to do runtime overflow checks at<00:15:43.639> two<00:15:44.639> uh<00:15:44.800> locations<00:15:45.199> in<00:15:45.360> the<00:15:45.480> code<00:15:45.800> for<00:15:46.279> when 00:15:46.389 --> 00:15:46.399 align:start position:0% at two uh locations in the code for when 00:15:46.399 --> 00:15:49.069 align:start position:0% at two uh locations in the code for when we<00:15:46.519> execute<00:15:46.839> call<00:15:47.040> F<00:15:47.199> or<00:15:47.319> jump<00:15:47.600> F<00:15:47.920> we<00:15:48.319> get<00:15:48.720> the 00:15:49.069 --> 00:15:49.079 align:start position:0% we execute call F or jump F we get the 00:15:49.079 --> 00:15:50.829 align:start position:0% we execute call F or jump F we get the current<00:15:49.399> runtime<00:15:49.759> stack<00:15:50.079> height<00:15:50.360> we<00:15:50.519> add<00:15:50.680> it 00:15:50.829 --> 00:15:50.839 align:start position:0% current runtime stack height we add it 00:15:50.839 --> 00:15:54.670 align:start position:0% current runtime stack height we add it up<00:15:51.120> with<00:15:51.720> maximum<00:15:52.199> stack<00:15:52.639> height<00:15:52.959> of<00:15:53.120> the 00:15:54.670 --> 00:15:54.680 align:start position:0% up with maximum stack height of the 00:15:54.680 --> 00:15:57.150 align:start position:0% up with maximum stack height of the call<00:15:55.680> if<00:15:55.880> this<00:15:56.000> sum<00:15:56.240> is<00:15:56.399> above<00:15:56.639> the<00:15:56.880> stack 00:15:57.150 --> 00:15:57.160 align:start position:0% call if this sum is above the stack 00:15:57.160 --> 00:15:58.590 align:start position:0% call if this sum is above the stack height<00:15:57.319> limit<00:15:57.560> we<00:15:57.639> do<00:15:57.800> not<00:15:57.920> allow<00:15:58.160> callif<00:15:58.480> a 00:15:58.590 --> 00:15:58.600 align:start position:0% height limit we do not allow callif a 00:15:58.600 --> 00:16:01.269 align:start position:0% height limit we do not allow callif a jump<00:15:59.040> we<00:15:59.199> exceptionally<00:15:59.800> abort<00:16:00.240> at<00:16:00.560> call<00:16:00.839> F<00:16:01.079> or 00:16:01.269 --> 00:16:01.279 align:start position:0% jump we exceptionally abort at call F or 00:16:01.279 --> 00:16:06.470 align:start position:0% jump we exceptionally abort at call F or jump<00:16:01.839> F<00:16:02.839> otherwise<00:16:03.680> uh<00:16:04.560> um<00:16:05.560> execution<00:16:06.199> could 00:16:06.470 --> 00:16:06.480 align:start position:0% jump F otherwise uh um execution could 00:16:06.480 --> 00:16:09.150 align:start position:0% jump F otherwise uh um execution could overflow<00:16:07.079> execution<00:16:07.480> of<00:16:07.680> this<00:16:08.240> uh<00:16:08.720> eof 00:16:09.150 --> 00:16:09.160 align:start position:0% overflow execution of this uh eof 00:16:09.160 --> 00:16:11.710 align:start position:0% overflow execution of this uh eof function<00:16:10.079> so<00:16:10.279> this<00:16:10.399> is<00:16:10.560> how<00:16:10.759> overflows<00:16:11.440> are 00:16:11.710 --> 00:16:11.720 align:start position:0% function so this is how overflows are 00:16:11.720 --> 00:16:14.150 align:start position:0% function so this is how overflows are handled<00:16:12.279> and<00:16:12.720> uh<00:16:13.199> one<00:16:13.440> final<00:16:13.759> thing<00:16:13.920> that<00:16:14.040> I 00:16:14.150 --> 00:16:14.160 align:start position:0% handled and uh one final thing that I 00:16:14.160 --> 00:16:16.230 align:start position:0% handled and uh one final thing that I wanted<00:16:14.399> to<00:16:14.519> mention<00:16:15.040> is<00:16:15.600> non-<00:16:15.839> returning 00:16:16.230 --> 00:16:16.240 align:start position:0% wanted to mention is non- returning 00:16:16.240 --> 00:16:18.790 align:start position:0% wanted to mention is non- returning functions<00:16:16.600> and<00:16:16.800> jump<00:16:17.120> F<00:16:17.920> these<00:16:18.079> are<00:16:18.360> defined 00:16:18.790 --> 00:16:18.800 align:start position:0% functions and jump F these are defined 00:16:18.800 --> 00:16:22.069 align:start position:0% functions and jump F these are defined in<00:16:18.959> their<00:16:19.199> own<00:16:19.480> EIP<00:16:20.319> but<00:16:20.959> they<00:16:21.120> are<00:16:21.720> closely 00:16:22.069 --> 00:16:22.079 align:start position:0% in their own EIP but they are closely 00:16:22.079 --> 00:16:23.829 align:start position:0% in their own EIP but they are closely related<00:16:22.360> to<00:16:22.480> stack<00:16:22.720> validation<00:16:23.360> and 00:16:23.829 --> 00:16:23.839 align:start position:0% related to stack validation and 00:16:23.839 --> 00:16:25.710 align:start position:0% related to stack validation and partially<00:16:24.279> motivated<00:16:24.800> by<00:16:24.920> Stack<00:16:25.199> validation 00:16:25.710 --> 00:16:25.720 align:start position:0% partially motivated by Stack validation 00:16:25.720 --> 00:16:28.710 align:start position:0% partially motivated by Stack validation I<00:16:25.800> would<00:16:26.079> say<00:16:27.079> so<00:16:27.319> non<00:16:27.959> functions<00:16:28.279> are<00:16:28.519> those 00:16:28.710 --> 00:16:28.720 align:start position:0% I would say so non functions are those 00:16:28.720 --> 00:16:31.350 align:start position:0% I would say so non functions are those that<00:16:29.000> do<00:16:29.160> not<00:16:29.519> return<00:16:29.920> control<00:16:30.440> back<00:16:30.759> to<00:16:31.120> a 00:16:31.350 --> 00:16:31.360 align:start position:0% that do not return control back to a 00:16:31.360 --> 00:16:33.910 align:start position:0% that do not return control back to a caller<00:16:31.839> they<00:16:32.000> do<00:16:32.120> not<00:16:32.319> execute<00:16:32.720> red<00:16:33.040> f 00:16:33.910 --> 00:16:33.920 align:start position:0% caller they do not execute red f 00:16:33.920 --> 00:16:35.910 align:start position:0% caller they do not execute red f instruction<00:16:34.920> or<00:16:35.120> you<00:16:35.199> could<00:16:35.360> think<00:16:35.519> of<00:16:35.680> them 00:16:35.910 --> 00:16:35.920 align:start position:0% instruction or you could think of them 00:16:35.920 --> 00:16:39.069 align:start position:0% instruction or you could think of them as<00:16:36.880> functions<00:16:37.319> that<00:16:37.680> and<00:16:38.160> entire<00:16:38.639> contract 00:16:39.069 --> 00:16:39.079 align:start position:0% as functions that and entire contract 00:16:39.079 --> 00:16:40.870 align:start position:0% as functions that and entire contract execution<00:16:39.720> with<00:16:39.880> instructions<00:16:40.360> like<00:16:40.480> stop 00:16:40.870 --> 00:16:40.880 align:start position:0% execution with instructions like stop 00:16:40.880 --> 00:16:42.710 align:start position:0% execution with instructions like stop return<00:16:41.160> revert 00:16:42.710 --> 00:16:42.720 align:start position:0% return revert 00:16:42.720 --> 00:16:45.509 align:start position:0% return revert Etc<00:16:43.720> uh<00:16:43.880> how<00:16:44.079> is<00:16:44.279> this<00:16:44.519> relevant<00:16:44.959> to<00:16:45.120> stack 00:16:45.509 --> 00:16:45.519 align:start position:0% Etc uh how is this relevant to stack 00:16:45.519 --> 00:16:48.910 align:start position:0% Etc uh how is this relevant to stack validation<00:16:46.519> um<00:16:47.160> so<00:16:47.519> when<00:16:47.720> we<00:16:47.959> validate<00:16:48.440> a<00:16:48.639> call 00:16:48.910 --> 00:16:48.920 align:start position:0% validation um so when we validate a call 00:16:48.920 --> 00:16:50.829 align:start position:0% validation um so when we validate a call to<00:16:49.120> such<00:16:49.279> a<00:16:49.440> non-returning 00:16:50.829 --> 00:16:50.839 align:start position:0% to such a non-returning 00:16:50.839 --> 00:16:52.870 align:start position:0% to such a non-returning function<00:16:51.839> if<00:16:52.040> there's<00:16:52.279> some<00:16:52.519> code 00:16:52.870 --> 00:16:52.880 align:start position:0% function if there's some code 00:16:52.880 --> 00:16:55.509 align:start position:0% function if there's some code immediately<00:16:53.319> following<00:16:53.800> this<00:16:54.199> call<00:16:55.160> uh<00:16:55.319> this 00:16:55.509 --> 00:16:55.519 align:start position:0% immediately following this call uh this 00:16:55.519 --> 00:16:57.189 align:start position:0% immediately following this call uh this code<00:16:55.839> is<00:16:56.000> never<00:16:56.240> going<00:16:56.399> to<00:16:56.519> be<00:16:56.680> executed<00:16:57.079> at 00:16:57.189 --> 00:16:57.199 align:start position:0% code is never going to be executed at 00:16:57.199 --> 00:16:59.550 align:start position:0% code is never going to be executed at run<00:16:57.440> time<00:16:57.639> because<00:16:57.880> this<00:16:58.040> call<00:16:58.319> is<00:16:58.639> not 00:16:59.550 --> 00:16:59.560 align:start position:0% run time because this call is not 00:16:59.560 --> 00:17:02.430 align:start position:0% run time because this call is not returning<00:17:00.560> this<00:17:00.759> means<00:17:01.240> that<00:17:01.639> we<00:17:01.800> do<00:17:01.959> not<00:17:02.160> need 00:17:02.430 --> 00:17:02.440 align:start position:0% returning this means that we do not need 00:17:02.440 --> 00:17:04.350 align:start position:0% returning this means that we do not need and<00:17:02.600> we<00:17:02.720> should<00:17:02.959> not<00:17:03.240> validate<00:17:03.720> this<00:17:03.959> code 00:17:04.350 --> 00:17:04.360 align:start position:0% and we should not validate this code 00:17:04.360 --> 00:17:05.909 align:start position:0% and we should not validate this code following<00:17:04.760> the<00:17:04.839> call<00:17:05.039> to<00:17:05.160> non 00:17:05.909 --> 00:17:05.919 align:start position:0% following the call to non 00:17:05.919 --> 00:17:08.750 align:start position:0% following the call to non returning<00:17:06.919> instead<00:17:07.280> we<00:17:07.439> should<00:17:08.160> uh<00:17:08.439> consider 00:17:08.750 --> 00:17:08.760 align:start position:0% returning instead we should uh consider 00:17:08.760 --> 00:17:10.669 align:start position:0% returning instead we should uh consider it<00:17:08.880> unreachable<00:17:09.400> and<00:17:09.600> reject<00:17:09.919> it<00:17:10.280> as<00:17:10.400> we<00:17:10.520> do 00:17:10.669 --> 00:17:10.679 align:start position:0% it unreachable and reject it as we do 00:17:10.679 --> 00:17:12.750 align:start position:0% it unreachable and reject it as we do with<00:17:10.839> other<00:17:11.039> unreachable<00:17:11.559> code<00:17:12.280> uh<00:17:12.400> so<00:17:12.559> to 00:17:12.750 --> 00:17:12.760 align:start position:0% with other unreachable code uh so to 00:17:12.760 --> 00:17:14.429 align:start position:0% with other unreachable code uh so to make<00:17:13.000> this<00:17:13.160> work<00:17:13.439> stack<00:17:13.679> validation<00:17:14.120> has<00:17:14.240> to 00:17:14.429 --> 00:17:14.439 align:start position:0% make this work stack validation has to 00:17:14.439 --> 00:17:16.230 align:start position:0% make this work stack validation has to detect<00:17:14.880> calls<00:17:15.120> to<00:17:15.240> non-<00:17:15.439> returning<00:17:15.799> functions 00:17:16.230 --> 00:17:16.240 align:start position:0% detect calls to non- returning functions 00:17:16.240 --> 00:17:18.789 align:start position:0% detect calls to non- returning functions somehow<00:17:17.240> for<00:17:17.480> that<00:17:17.600> we<00:17:17.760> have<00:17:17.880> a<00:17:18.039> special<00:17:18.360> flag 00:17:18.789 --> 00:17:18.799 align:start position:0% somehow for that we have a special flag 00:17:18.799 --> 00:17:21.270 align:start position:0% somehow for that we have a special flag in<00:17:19.000> the<00:17:19.160> EF<00:17:19.600> header<00:17:20.039> in<00:17:20.439> the<00:17:20.720> functions 00:17:21.270 --> 00:17:21.280 align:start position:0% in the EF header in the functions 00:17:21.280 --> 00:17:24.069 align:start position:0% in the EF header in the functions metadata<00:17:22.280> so<00:17:22.480> when<00:17:22.679> stack<00:17:22.959> validation<00:17:23.880> uh 00:17:24.069 --> 00:17:24.079 align:start position:0% metadata so when stack validation uh 00:17:24.079 --> 00:17:26.990 align:start position:0% metadata so when stack validation uh detects<00:17:24.839> a<00:17:25.199> call<00:17:26.079> when<00:17:26.240> it<00:17:26.360> sees<00:17:26.559> a<00:17:26.679> call<00:17:26.919> it 00:17:26.990 --> 00:17:27.000 align:start position:0% detects a call when it sees a call it 00:17:27.000 --> 00:17:28.350 align:start position:0% detects a call when it sees a call it checks<00:17:27.280> this<00:17:27.439> flag<00:17:27.760> whether<00:17:27.919> it's<00:17:28.039> returning 00:17:28.350 --> 00:17:28.360 align:start position:0% checks this flag whether it's returning 00:17:28.360 --> 00:17:30.029 align:start position:0% checks this flag whether it's returning or<00:17:28.439> non<00:17:28.559> rur<00:17:29.120> if<00:17:29.200> it's<00:17:29.320> a<00:17:29.440> call<00:17:29.640> to<00:17:29.799> non- 00:17:30.029 --> 00:17:30.039 align:start position:0% or non rur if it's a call to non- 00:17:30.039 --> 00:17:31.990 align:start position:0% or non rur if it's a call to non- returning<00:17:30.720> function<00:17:31.200> it<00:17:31.360> considers<00:17:31.840> this 00:17:31.990 --> 00:17:32.000 align:start position:0% returning function it considers this 00:17:32.000 --> 00:17:34.510 align:start position:0% returning function it considers this call<00:17:32.240> to<00:17:32.320> be<00:17:32.440> a<00:17:32.559> terminated<00:17:33.120> instruction<00:17:33.760> and 00:17:34.510 --> 00:17:34.520 align:start position:0% call to be a terminated instruction and 00:17:34.520 --> 00:17:37.029 align:start position:0% call to be a terminated instruction and then<00:17:35.520> uh<00:17:35.760> in<00:17:35.880> the<00:17:36.000> end<00:17:36.240> then<00:17:36.400> if<00:17:36.559> there's<00:17:36.880> some 00:17:37.029 --> 00:17:37.039 align:start position:0% then uh in the end then if there's some 00:17:37.039 --> 00:17:39.350 align:start position:0% then uh in the end then if there's some code<00:17:37.240> immediately<00:17:37.640> following<00:17:38.039> it<00:17:38.440> it<00:17:38.840> it<00:17:39.160> may 00:17:39.350 --> 00:17:39.360 align:start position:0% code immediately following it it it may 00:17:39.360 --> 00:17:41.270 align:start position:0% code immediately following it it it may be<00:17:39.480> unreachable<00:17:40.039> unless<00:17:40.360> there<00:17:40.520> was<00:17:40.760> some 00:17:41.270 --> 00:17:41.280 align:start position:0% be unreachable unless there was some 00:17:41.280 --> 00:17:43.430 align:start position:0% be unreachable unless there was some previously<00:17:41.679> seen<00:17:41.960> forward<00:17:42.320> jump<00:17:42.600> into<00:17:42.799> it<00:17:43.280> so 00:17:43.430 --> 00:17:43.440 align:start position:0% previously seen forward jump into it so 00:17:43.440 --> 00:17:44.750 align:start position:0% previously seen forward jump into it so this<00:17:43.559> is<00:17:43.679> how<00:17:43.799> it<00:17:43.919> works<00:17:44.200> what's<00:17:44.400> important 00:17:44.750 --> 00:17:44.760 align:start position:0% this is how it works what's important 00:17:44.760 --> 00:17:46.870 align:start position:0% this is how it works what's important here<00:17:44.960> is<00:17:45.120> that<00:17:45.320> calls<00:17:45.600> to<00:17:45.799> returning<00:17:46.440> and<00:17:46.600> non- 00:17:46.870 --> 00:17:46.880 align:start position:0% here is that calls to returning and non- 00:17:46.880 --> 00:17:48.909 align:start position:0% here is that calls to returning and non- returning<00:17:47.280> functions<00:17:47.679> are<00:17:47.880> validated<00:17:48.480> very 00:17:48.909 --> 00:17:48.919 align:start position:0% returning functions are validated very 00:17:48.919 --> 00:17:51.110 align:start position:0% returning functions are validated very differently<00:17:49.919> so<00:17:50.120> for<00:17:50.320> calls<00:17:50.559> to<00:17:50.720> returning 00:17:51.110 --> 00:17:51.120 align:start position:0% differently so for calls to returning 00:17:51.120 --> 00:17:52.510 align:start position:0% differently so for calls to returning functions<00:17:51.440> you<00:17:51.559> have<00:17:51.679> to<00:17:51.799> take<00:17:51.960> into<00:17:52.200> account 00:17:52.510 --> 00:17:52.520 align:start position:0% functions you have to take into account 00:17:52.520 --> 00:17:54.630 align:start position:0% functions you have to take into account how<00:17:52.640> many<00:17:53.320> values<00:17:53.640> were<00:17:54.000> returned<00:17:54.360> put<00:17:54.520> them 00:17:54.630 --> 00:17:54.640 align:start position:0% how many values were returned put them 00:17:54.640 --> 00:17:56.350 align:start position:0% how many values were returned put them on<00:17:54.840> stack<00:17:55.120> and<00:17:55.280> continue<00:17:55.640> validation<00:17:56.200> and 00:17:56.350 --> 00:17:56.360 align:start position:0% on stack and continue validation and 00:17:56.360 --> 00:17:57.750 align:start position:0% on stack and continue validation and calls<00:17:56.679> to<00:17:56.799> non-<00:17:57.039> returning<00:17:57.400> ad<00:17:57.600> just 00:17:57.750 --> 00:17:57.760 align:start position:0% calls to non- returning ad just 00:17:57.760 --> 00:17:59.470 align:start position:0% calls to non- returning ad just terminating<00:17:58.200> instructions 00:17:59.470 --> 00:17:59.480 align:start position:0% terminating instructions 00:17:59.480 --> 00:18:02.669 align:start position:0% terminating instructions given<00:17:59.760> this<00:18:00.039> difference<00:18:00.520> I<00:18:00.600> would<00:18:01.120> say<00:18:02.120> uh<00:18:02.440> a 00:18:02.669 --> 00:18:02.679 align:start position:0% given this difference I would say uh a 00:18:02.679 --> 00:18:04.990 align:start position:0% given this difference I would say uh a separate<00:18:03.240> instruction<00:18:03.760> for<00:18:04.000> C<00:18:04.559> return<00:18:04.840> is 00:18:04.990 --> 00:18:05.000 align:start position:0% separate instruction for C return is 00:18:05.000 --> 00:18:07.470 align:start position:0% separate instruction for C return is already<00:18:05.400> Justified<00:18:06.039> so<00:18:06.559> this<00:18:06.880> is<00:18:07.080> exactly 00:18:07.470 --> 00:18:07.480 align:start position:0% already Justified so this is exactly 00:18:07.480 --> 00:18:09.789 align:start position:0% already Justified so this is exactly what<00:18:07.679> jump<00:18:08.000> F<00:18:08.200> instruction<00:18:08.799> is<00:18:09.440> if<00:18:09.520> you<00:18:09.640> need 00:18:09.789 --> 00:18:09.799 align:start position:0% what jump F instruction is if you need 00:18:09.799 --> 00:18:13.470 align:start position:0% what jump F instruction is if you need to<00:18:09.919> do<00:18:10.080> a<00:18:10.200> call<00:18:10.360> to<00:18:10.520> non<00:18:11.120> function<00:18:11.960> you<00:18:12.960> uh<00:18:13.200> use 00:18:13.470 --> 00:18:13.480 align:start position:0% to do a call to non function you uh use 00:18:13.480 --> 00:18:15.789 align:start position:0% to do a call to non function you uh use jump<00:18:13.760> f<00:18:13.919> for<00:18:14.080> that<00:18:14.240> call<00:18:14.480> F<00:18:14.640> to<00:18:14.799> non<00:18:14.960> returning 00:18:15.789 --> 00:18:15.799 align:start position:0% jump f for that call F to non returning 00:18:15.799 --> 00:18:18.950 align:start position:0% jump f for that call F to non returning is<00:18:15.960> not<00:18:16.200> allowed<00:18:16.960> in 00:18:18.950 --> 00:18:18.960 align:start position:0% is not allowed in 00:18:18.960 --> 00:18:22.470 align:start position:0% is not allowed in fact<00:18:19.960> uh<00:18:20.120> jump<00:18:20.440> F<00:18:20.720> also<00:18:21.039> has<00:18:21.799> different<00:18:22.159> use 00:18:22.470 --> 00:18:22.480 align:start position:0% fact uh jump F also has different use 00:18:22.480 --> 00:18:24.230 align:start position:0% fact uh jump F also has different use case<00:18:22.640> it<00:18:22.799> can<00:18:22.919> be<00:18:23.039> used<00:18:23.440> with<00:18:23.679> returning 00:18:24.230 --> 00:18:24.240 align:start position:0% case it can be used with returning 00:18:24.240 --> 00:18:27.070 align:start position:0% case it can be used with returning functions<00:18:24.919> but<00:18:25.440> uh<00:18:25.640> this<00:18:25.919> does<00:18:26.120> not<00:18:26.320> fit<00:18:26.720> this 00:18:27.070 --> 00:18:27.080 align:start position:0% functions but uh this does not fit this 00:18:27.080 --> 00:18:29.110 align:start position:0% functions but uh this does not fit this presentation<00:18:28.080> but<00:18:28.240> you<00:18:28.360> can<00:18:28.840> read<00:18:28.960> more 00:18:29.110 --> 00:18:29.120 align:start position:0% presentation but you can read more 00:18:29.120 --> 00:18:32.270 align:start position:0% presentation but you can read more details<00:18:29.520> in<00:18:29.640> the<00:18:29.760> EIP<00:18:30.440> or<00:18:31.440> some<00:18:31.679> discussion<00:18:32.080> at 00:18:32.270 --> 00:18:32.280 align:start position:0% details in the EIP or some discussion at 00:18:32.280 --> 00:18:34.029 align:start position:0% details in the EIP or some discussion at this<00:18:32.720> another 00:18:34.029 --> 00:18:34.039 align:start position:0% this another 00:18:34.039 --> 00:18:36.750 align:start position:0% this another link<00:18:35.039> and<00:18:35.240> this<00:18:35.360> is<00:18:35.640> what<00:18:35.840> all<00:18:36.120> that<00:18:36.240> I<00:18:36.360> wanted 00:18:36.750 --> 00:18:36.760 align:start position:0% link and this is what all that I wanted 00:18:36.760 --> 00:18:44.270 align:start position:0% link and this is what all that I wanted to<00:18:36.919> say<00:18:37.159> about<00:18:37.440> this<00:18:37.720> thank 00:18:44.270 --> 00:18:44.280 align:start position:0% 00:18:44.280 --> 00:18:46.950 align:start position:0% you<00:18:45.280> thanks<00:18:45.480> a<00:18:45.679> lot<00:18:46.080> that<00:18:46.240> was<00:18:46.440> a<00:18:46.760> very 00:18:46.950 --> 00:18:46.960 align:start position:0% you thanks a lot that was a very 00:18:46.960 --> 00:18:50.190 align:start position:0% you thanks a lot that was a very interesting<00:18:47.440> presentation<00:18:48.400> so<00:18:49.240> let's<00:18:49.520> start 00:18:50.190 --> 00:18:50.200 align:start position:0% interesting presentation so let's start 00:18:50.200 --> 00:18:53.149 align:start position:0% interesting presentation so let's start uh<00:18:50.600> with<00:18:51.120> uh<00:18:51.320> the<00:18:51.600> questions<00:18:52.600> uh<00:18:52.760> the<00:18:52.919> most 00:18:53.149 --> 00:18:53.159 align:start position:0% uh with uh the questions uh the most 00:18:53.159 --> 00:18:57.549 align:start position:0% uh with uh the questions uh the most popular<00:18:53.559> one<00:18:54.120> is<00:18:55.159> um<00:18:56.159> uh<00:18:56.760> good<00:18:57.280> stack 00:18:57.549 --> 00:18:57.559 align:start position:0% popular one is um uh good stack 00:18:57.559 --> 00:18:59.909 align:start position:0% popular one is um uh good stack validation<00:18:58.240> allowed<00:18:58.840> translation<00:18:59.559> to<00:18:59.760> a 00:18:59.909 --> 00:18:59.919 align:start position:0% validation allowed translation to a 00:18:59.919 --> 00:19:01.470 align:start position:0% validation allowed translation to a register<00:19:00.400> based<00:19:00.760> instruction<00:19:01.200> set 00:19:01.470 --> 00:19:01.480 align:start position:0% register based instruction set 00:19:01.480 --> 00:19:05.510 align:start position:0% register based instruction set internally<00:19:02.640> reducing<00:19:03.760> dispatch<00:19:04.760> overhead<00:19:05.360> in 00:19:05.510 --> 00:19:05.520 align:start position:0% internally reducing dispatch overhead in 00:19:05.520 --> 00:19:07.190 align:start position:0% internally reducing dispatch overhead in The<00:19:05.640> Interpreter 00:19:07.190 --> 00:19:07.200 align:start position:0% The Interpreter 00:19:07.200 --> 00:19:12.510 align:start position:0% The Interpreter loop<00:19:08.200> I<00:19:08.320> think<00:19:08.559> definitely<00:19:09.039> it 00:19:12.510 --> 00:19:12.520 align:start position:0% 00:19:12.520 --> 00:19:16.789 align:start position:0% can<00:19:13.520> any<00:19:13.799> any<00:19:14.039> translation<00:19:14.559> is<00:19:15.240> easier<00:19:16.159> uh<00:19:16.600> in 00:19:16.789 --> 00:19:16.799 align:start position:0% can any any translation is easier uh in 00:19:16.799 --> 00:19:19.750 align:start position:0% can any any translation is easier uh in eof<00:19:17.559> given<00:19:17.840> that<00:19:18.000> we<00:19:18.159> have<00:19:18.640> we<00:19:18.760> do<00:19:18.880> not<00:19:19.080> have 00:19:19.750 --> 00:19:19.760 align:start position:0% eof given that we have we do not have 00:19:19.760 --> 00:19:21.230 align:start position:0% eof given that we have we do not have Dynamic<00:19:20.080> jumps<00:19:20.440> that's<00:19:20.559> the<00:19:20.679> main<00:19:20.880> reason 00:19:21.230 --> 00:19:21.240 align:start position:0% Dynamic jumps that's the main reason 00:19:21.240 --> 00:19:24.230 align:start position:0% Dynamic jumps that's the main reason that<00:19:21.760> we<00:19:21.880> can<00:19:22.080> do<00:19:22.320> jittin<00:19:22.880> we<00:19:23.000> can<00:19:23.400> compile<00:19:23.799> to 00:19:24.230 --> 00:19:24.240 align:start position:0% that we can do jittin we can compile to 00:19:24.240 --> 00:19:28.390 align:start position:0% that we can do jittin we can compile to whatever<00:19:25.280> backand<00:19:26.280> uh<00:19:26.440> it's<00:19:26.799> yeah<00:19:27.600> there<00:19:27.720> are 00:19:28.390 --> 00:19:28.400 align:start position:0% whatever backand uh it's yeah there are 00:19:28.400 --> 00:19:30.990 align:start position:0% whatever backand uh it's yeah there are various<00:19:28.840> ideas<00:19:29.200> about<00:19:30.080> what<00:19:30.280> EF<00:19:30.720> can<00:19:30.840> be 00:19:30.990 --> 00:19:31.000 align:start position:0% various ideas about what EF can be 00:19:31.000 --> 00:19:36.549 align:start position:0% various ideas about what EF can be compiled<00:19:31.440> to<00:19:32.360> uh<00:19:32.880> uh<00:19:33.400> not 00:19:36.549 --> 00:19:36.559 align:start position:0% 00:19:36.559 --> 00:19:40.350 align:start position:0% yeah<00:19:37.559> interesting<00:19:37.960> topic<00:19:38.720> yeah<00:19:39.720> okay<00:19:40.200> the 00:19:40.350 --> 00:19:40.360 align:start position:0% yeah interesting topic yeah okay the 00:19:40.360 --> 00:19:43.350 align:start position:0% yeah interesting topic yeah okay the next<00:19:40.640> question<00:19:41.000> is<00:19:41.559> since<00:19:42.000> stack<00:19:42.360> size<00:19:42.679> can 00:19:43.350 --> 00:19:43.360 align:start position:0% next question is since stack size can 00:19:43.360 --> 00:19:46.350 align:start position:0% next question is since stack size can vary<00:19:43.679> with<00:19:43.880> recursion<00:19:44.679> which<00:19:44.880> is<00:19:45.159> only<00:19:45.440> known 00:19:46.350 --> 00:19:46.360 align:start position:0% vary with recursion which is only known 00:19:46.360 --> 00:19:48.549 align:start position:0% vary with recursion which is only known uh<00:19:46.480> at<00:19:46.679> run<00:19:46.960> time<00:19:47.480> how<00:19:47.679> can<00:19:47.960> this<00:19:48.200> method 00:19:48.549 --> 00:19:48.559 align:start position:0% uh at run time how can this method 00:19:48.559 --> 00:19:52.350 align:start position:0% uh at run time how can this method ensure<00:19:49.320> St<00:19:49.799> stack<00:19:50.280> Overflow<00:19:51.120> is<00:19:51.280> detected 00:19:52.350 --> 00:19:52.360 align:start position:0% ensure St stack Overflow is detected 00:19:52.360 --> 00:19:55.310 align:start position:0% ensure St stack Overflow is detected statically<00:19:53.360> good<00:19:53.600> question<00:19:54.120> so<00:19:54.600> it<00:19:54.760> is<00:19:55.120> we 00:19:55.310 --> 00:19:55.320 align:start position:0% statically good question so it is we 00:19:55.320 --> 00:19:59.510 align:start position:0% statically good question so it is we still<00:19:56.000> uh<00:19:56.679> uh<00:19:57.159> require<00:19:58.120> runtime<00:19:58.880> for<00:19:59.000> overflow 00:19:59.510 --> 00:19:59.520 align:start position:0% still uh uh require runtime for overflow 00:19:59.520 --> 00:20:01.669 align:start position:0% still uh uh require runtime for overflow we<00:19:59.720> just<00:20:00.000> don't<00:20:00.240> do<00:20:00.480> them<00:20:01.080> every<00:20:01.320> time<00:20:01.520> at 00:20:01.669 --> 00:20:01.679 align:start position:0% we just don't do them every time at 00:20:01.679 --> 00:20:03.950 align:start position:0% we just don't do them every time at every 00:20:03.950 --> 00:20:03.960 align:start position:0% 00:20:03.960 --> 00:20:07.149 align:start position:0% instruction<00:20:04.960> so<00:20:05.559> uh<00:20:06.200> the<00:20:06.360> recursive<00:20:06.840> calls 00:20:07.149 --> 00:20:07.159 align:start position:0% instruction so uh the recursive calls 00:20:07.159 --> 00:20:09.470 align:start position:0% instruction so uh the recursive calls will<00:20:07.360> still<00:20:08.080> do<00:20:08.320> the<00:20:08.480> Overflow<00:20:08.960> check<00:20:09.280> when 00:20:09.470 --> 00:20:09.480 align:start position:0% will still do the Overflow check when 00:20:09.480 --> 00:20:11.430 align:start position:0% will still do the Overflow check when they<00:20:09.600> do<00:20:09.840> a<00:20:10.000> call<00:20:10.559> callif<00:20:10.919> or<00:20:11.039> jump<00:20:11.240> off 00:20:11.430 --> 00:20:11.440 align:start position:0% they do a call callif or jump off 00:20:11.440 --> 00:20:14.549 align:start position:0% they do a call callif or jump off instruction<00:20:12.000> and<00:20:12.280> in<00:20:12.480> case<00:20:13.080> uh<00:20:13.320> this<00:20:13.840> call<00:20:14.240> May 00:20:14.549 --> 00:20:14.559 align:start position:0% instruction and in case uh this call May 00:20:14.559 --> 00:20:16.669 align:start position:0% instruction and in case uh this call May overflow<00:20:15.240> this<00:20:15.559> call<00:20:15.799> is<00:20:15.919> not<00:20:16.080> going<00:20:16.240> to<00:20:16.400> be 00:20:16.669 --> 00:20:16.679 align:start position:0% overflow this call is not going to be 00:20:16.679 --> 00:20:18.669 align:start position:0% overflow this call is not going to be succeeded<00:20:17.200> so<00:20:17.600> overflow<00:20:18.039> checks<00:20:18.240> are<00:20:18.400> not 00:20:18.669 --> 00:20:18.679 align:start position:0% succeeded so overflow checks are not 00:20:18.679 --> 00:20:20.630 align:start position:0% succeeded so overflow checks are not checked<00:20:19.039> completely<00:20:19.679> statically<00:20:20.400> that's 00:20:20.630 --> 00:20:20.640 align:start position:0% checked completely statically that's 00:20:20.640 --> 00:20:22.390 align:start position:0% checked completely statically that's that's<00:20:20.799> the 00:20:22.390 --> 00:20:22.400 align:start position:0% that's the 00:20:22.400 --> 00:20:26.909 align:start position:0% that's the answer<00:20:23.640> great<00:20:24.640> uh<00:20:25.240> so<00:20:25.760> the<00:20:26.000> next<00:20:26.320> question<00:20:26.760> I 00:20:26.909 --> 00:20:26.919 align:start position:0% answer great uh so the next question I 00:20:26.919 --> 00:20:29.510 align:start position:0% answer great uh so the next question I think<00:20:27.440> uh<00:20:27.720> in<00:20:27.840> the<00:20:28.039> beginning<00:20:28.760> you<00:20:28.960> mentioned 00:20:29.510 --> 00:20:29.520 align:start position:0% think uh in the beginning you mentioned 00:20:29.520 --> 00:20:32.149 align:start position:0% think uh in the beginning you mentioned that<00:20:29.880> uh<00:20:30.080> some<00:20:30.440> compiler<00:20:31.159> optimizations 00:20:32.149 --> 00:20:32.159 align:start position:0% that uh some compiler optimizations 00:20:32.159 --> 00:20:34.789 align:start position:0% that uh some compiler optimizations won't<00:20:32.480> be<00:20:32.720> worth<00:20:32.960> it<00:20:33.559> so<00:20:33.799> I<00:20:34.000> guess<00:20:34.400> uh<00:20:34.559> which 00:20:34.789 --> 00:20:34.799 align:start position:0% won't be worth it so I guess uh which 00:20:34.799 --> 00:20:36.830 align:start position:0% won't be worth it so I guess uh which compilers<00:20:35.280> optimizations<00:20:36.120> won't<00:20:36.320> be<00:20:36.440> worth 00:20:36.830 --> 00:20:36.840 align:start position:0% compilers optimizations won't be worth 00:20:36.840 --> 00:20:39.390 align:start position:0% compilers optimizations won't be worth yeah<00:20:37.240> so<00:20:37.760> I<00:20:37.880> refer<00:20:38.280> to<00:20:38.559> this<00:20:38.760> one<00:20:39.000> specific 00:20:39.390 --> 00:20:39.400 align:start position:0% yeah so I refer to this one specific 00:20:39.400 --> 00:20:43.230 align:start position:0% yeah so I refer to this one specific case<00:20:39.720> that<00:20:40.320> uh<00:20:40.559> was<00:20:41.039> pretty<00:20:41.360> common<00:20:41.720> for<00:20:42.520> our 00:20:43.230 --> 00:20:43.240 align:start position:0% case that uh was pretty common for our 00:20:43.240 --> 00:20:46.830 align:start position:0% case that uh was pretty common for our uh<00:20:43.400> initial<00:20:44.320> idea<00:20:44.760> of<00:20:44.880> Stack<00:20:45.520> validation<00:20:46.520> uh 00:20:46.830 --> 00:20:46.840 align:start position:0% uh initial idea of Stack validation uh 00:20:46.840 --> 00:20:49.630 align:start position:0% uh initial idea of Stack validation uh there<00:20:47.799> uh<00:20:48.080> the<00:20:48.240> optimization<00:20:49.000> that<00:20:49.159> I<00:20:49.280> meant 00:20:49.630 --> 00:20:49.640 align:start position:0% there uh the optimization that I meant 00:20:49.640 --> 00:20:52.990 align:start position:0% there uh the optimization that I meant was<00:20:50.360> uh<00:20:51.240> the<00:20:51.520> application<00:20:52.120> that<00:20:52.640> solidity 00:20:52.990 --> 00:20:53.000 align:start position:0% was uh the application that solidity 00:20:53.000 --> 00:20:55.230 align:start position:0% was uh the application that solidity compiler<00:20:53.400> does<00:20:53.679> when<00:20:53.799> it<00:20:53.880> sees<00:20:54.559> uh<00:20:54.720> a<00:20:54.919> similar 00:20:55.230 --> 00:20:55.240 align:start position:0% compiler does when it sees uh a similar 00:20:55.240 --> 00:20:58.590 align:start position:0% compiler does when it sees uh a similar code<00:20:55.559> at<00:20:55.799> at<00:20:56.000> multiple<00:20:56.919> uh<00:20:57.440> points<00:20:57.840> in<00:20:58.039> the 00:20:58.590 --> 00:20:58.600 align:start position:0% code at at multiple uh points in the 00:20:58.600 --> 00:21:00.669 align:start position:0% code at at multiple uh points in the bite<00:20:58.840> code<00:20:59.200> it<00:20:59.600> gets<00:20:59.880> them<00:21:00.039> and<00:21:00.200> distracts 00:21:00.669 --> 00:21:00.679 align:start position:0% bite code it gets them and distracts 00:21:00.679 --> 00:21:03.950 align:start position:0% bite code it gets them and distracts them<00:21:00.840> into<00:21:01.039> a<00:21:01.159> common<00:21:02.000> Helper<00:21:02.960> but<00:21:03.280> like<00:21:03.799> with 00:21:03.950 --> 00:21:03.960 align:start position:0% them into a common Helper but like with 00:21:03.960 --> 00:21:05.710 align:start position:0% them into a common Helper but like with the<00:21:04.480> first<00:21:04.760> algorithm<00:21:05.240> there<00:21:05.320> was<00:21:05.520> some 00:21:05.710 --> 00:21:05.720 align:start position:0% the first algorithm there was some 00:21:05.720 --> 00:21:07.510 align:start position:0% the first algorithm there was some overhead<00:21:06.360> and<00:21:06.600> in<00:21:06.720> the<00:21:06.840> end<00:21:07.080> this<00:21:07.200> might<00:21:07.400> not 00:21:07.510 --> 00:21:07.520 align:start position:0% overhead and in the end this might not 00:21:07.520 --> 00:21:09.270 align:start position:0% overhead and in the end this might not be<00:21:07.679> worth<00:21:07.840> it<00:21:08.039> and<00:21:08.320> because<00:21:08.640> code<00:21:08.919> size<00:21:09.120> in<00:21:09.200> the 00:21:09.270 --> 00:21:09.280 align:start position:0% be worth it and because code size in the 00:21:09.280 --> 00:21:12.070 align:start position:0% be worth it and because code size in the end<00:21:09.679> may<00:21:09.880> increase<00:21:10.400> and<00:21:10.640> gas<00:21:10.919> also 00:21:12.070 --> 00:21:12.080 align:start position:0% end may increase and gas also 00:21:12.080 --> 00:21:17.230 align:start position:0% end may increase and gas also increased<00:21:13.279> mhm<00:21:14.279> uh<00:21:14.559> so<00:21:15.480> uh<00:21:15.679> what<00:21:16.000> does<00:21:17.000> why 00:21:17.230 --> 00:21:17.240 align:start position:0% increased mhm uh so uh what does why 00:21:17.240 --> 00:21:20.549 align:start position:0% increased mhm uh so uh what does why does<00:21:17.520> this<00:21:17.760> need<00:21:18.320> needs<00:21:18.640> to<00:21:18.799> be<00:21:19.039> part<00:21:19.279> of<00:21:19.760> eof 00:21:20.549 --> 00:21:20.559 align:start position:0% does this need needs to be part of eof 00:21:20.559 --> 00:21:23.549 align:start position:0% does this need needs to be part of eof instead<00:21:21.000> of<00:21:21.520> just<00:21:21.840> relying<00:21:22.279> on<00:21:22.440> the<00:21:22.640> compiler 00:21:23.549 --> 00:21:23.559 align:start position:0% instead of just relying on the compiler 00:21:23.559 --> 00:21:25.909 align:start position:0% instead of just relying on the compiler to<00:21:23.880> H<00:21:24.400> uh<00:21:24.520> to<00:21:24.720> handle<00:21:25.120> stack<00:21:25.559> access 00:21:25.909 --> 00:21:25.919 align:start position:0% to H uh to handle stack access 00:21:25.919 --> 00:21:32.149 align:start position:0% to H uh to handle stack access efficiently 00:21:32.149 --> 00:21:32.159 align:start position:0% 00:21:32.159 --> 00:21:35.070 align:start position:0% interesting 00:21:35.070 --> 00:21:35.080 align:start position:0% interesting 00:21:35.080 --> 00:21:38.230 align:start position:0% interesting um<00:21:36.080> well<00:21:36.240> I<00:21:36.320> would 00:21:38.230 --> 00:21:38.240 align:start position:0% um well I would 00:21:38.240 --> 00:21:41.149 align:start position:0% um well I would say<00:21:39.240> there<00:21:39.360> is<00:21:39.480> a<00:21:39.679> value<00:21:40.039> definitely<00:21:40.880> some 00:21:41.149 --> 00:21:41.159 align:start position:0% say there is a value definitely some 00:21:41.159 --> 00:21:43.870 align:start position:0% say there is a value definitely some value<00:21:41.520> in<00:21:41.840> ensuring<00:21:42.760> St<00:21:43.159> correctness<00:21:43.640> of<00:21:43.760> the 00:21:43.870 --> 00:21:43.880 align:start position:0% value in ensuring St correctness of the 00:21:43.880 --> 00:21:45.149 align:start position:0% value in ensuring St correctness of the bite<00:21:44.120> code 00:21:45.149 --> 00:21:45.159 align:start position:0% bite code 00:21:45.159 --> 00:21:48.669 align:start position:0% bite code itself<00:21:46.159> uh<00:21:46.279> because<00:21:46.640> it<00:21:46.919> can<00:21:47.919> it<00:21:48.200> bite<00:21:48.480> code 00:21:48.669 --> 00:21:48.679 align:start position:0% itself uh because it can it bite code 00:21:48.679 --> 00:21:50.470 align:start position:0% itself uh because it can it bite code itself<00:21:49.080> then<00:21:49.279> can<00:21:49.440> be<00:21:49.600> audited<00:21:50.080> or<00:21:50.240> can<00:21:50.360> be 00:21:50.470 --> 00:21:50.480 align:start position:0% itself then can be audited or can be 00:21:50.480 --> 00:21:52.070 align:start position:0% itself then can be audited or can be formally<00:21:50.880> verified<00:21:51.279> or<00:21:51.400> can<00:21:51.520> be<00:21:51.640> statically 00:21:52.070 --> 00:21:52.080 align:start position:0% formally verified or can be statically 00:21:52.080 --> 00:21:54.909 align:start position:0% formally verified or can be statically analyzed<00:21:52.679> so<00:21:53.360> St<00:21:53.679> validation<00:21:54.159> and<00:21:54.480> validation 00:21:54.909 --> 00:21:54.919 align:start position:0% analyzed so St validation and validation 00:21:54.919 --> 00:21:58.630 align:start position:0% analyzed so St validation and validation in<00:21:55.200> general<00:21:56.200> uh<00:21:56.679> uh<00:21:57.000> simplifies<00:21:57.799> these<00:21:58.000> tasks 00:21:58.630 --> 00:21:58.640 align:start position:0% in general uh uh simplifies these tasks 00:21:58.640 --> 00:22:02.350 align:start position:0% in general uh uh simplifies these tasks and<00:21:59.159> uh<00:21:59.840> uh<00:22:00.000> immensely<00:22:00.480> I<00:22:00.559> would<00:22:00.720> say<00:22:01.360> so 00:22:02.350 --> 00:22:02.360 align:start position:0% and uh uh immensely I would say so 00:22:02.360 --> 00:22:03.789 align:start position:0% and uh uh immensely I would say so that's<00:22:02.520> the<00:22:02.679> answer<00:22:02.960> I<00:22:03.039> think<00:22:03.240> so<00:22:03.520> if<00:22:03.640> it 00:22:03.789 --> 00:22:03.799 align:start position:0% that's the answer I think so if it 00:22:03.799 --> 00:22:06.549 align:start position:0% that's the answer I think so if it wouldn't<00:22:04.039> be<00:22:04.159> enforced<00:22:04.600> on<00:22:04.840> the<00:22:05.640> protocol 00:22:06.549 --> 00:22:06.559 align:start position:0% wouldn't be enforced on the protocol 00:22:06.559 --> 00:22:08.430 align:start position:0% wouldn't be enforced on the protocol level 00:22:08.430 --> 00:22:08.440 align:start position:0% level 00:22:08.440 --> 00:22:13.190 align:start position:0% level then<00:22:09.440> high<00:22:09.679> level<00:22:10.440> uh<00:22:11.000> the<00:22:11.200> same<00:22:12.200> only<00:22:12.720> the 00:22:13.190 --> 00:22:13.200 align:start position:0% then high level uh the same only the 00:22:13.200 --> 00:22:15.950 align:start position:0% then high level uh the same only the high<00:22:13.400> level<00:22:13.679> Lang<00:22:13.960> language<00:22:14.559> code<00:22:14.960> would<00:22:15.200> be 00:22:15.950 --> 00:22:15.960 align:start position:0% high level Lang language code would be 00:22:15.960 --> 00:22:17.149 align:start position:0% high level Lang language code would be available 00:22:17.149 --> 00:22:17.159 align:start position:0% available 00:22:17.159 --> 00:22:20.630 align:start position:0% available to<00:22:18.159> uh<00:22:18.559> to<00:22:18.720> use<00:22:19.039> these<00:22:19.279> benefits<00:22:19.760> I<00:22:19.840> think 00:22:20.630 --> 00:22:20.640 align:start position:0% to uh to use these benefits I think 00:22:20.640 --> 00:22:26.909 align:start position:0% to uh to use these benefits I think Soh<00:22:21.640> makes<00:22:22.360> sense<00:22:23.760> uh<00:22:24.760> so<00:22:25.240> the<00:22:25.440> next<00:22:25.720> one<00:22:26.240> is<00:22:26.679> uh 00:22:26.909 --> 00:22:26.919 align:start position:0% Soh makes sense uh so the next one is uh 00:22:26.919 --> 00:22:29.830 align:start position:0% Soh makes sense uh so the next one is uh if<00:22:27.120> the<00:22:27.279> code<00:22:27.679> passes<00:22:28.279> uh<00:22:28.640> stock<00:22:28.919> range 00:22:29.830 --> 00:22:29.840 align:start position:0% if the code passes uh stock range 00:22:29.840 --> 00:22:32.669 align:start position:0% if the code passes uh stock range validation<00:22:30.840> um<00:22:31.440> is<00:22:31.559> it<00:22:31.840> possible<00:22:32.360> that<00:22:32.559> there 00:22:32.669 --> 00:22:32.679 align:start position:0% validation um is it possible that there 00:22:32.679 --> 00:22:37.029 align:start position:0% validation um is it possible that there is<00:22:32.799> a<00:22:33.000> code<00:22:33.360> path<00:22:33.840> that<00:22:34.520> under<00:22:35.080> overflows<00:22:35.840> the 00:22:37.029 --> 00:22:37.039 align:start position:0% is a code path that under overflows the 00:22:37.039 --> 00:22:39.789 align:start position:0% is a code path that under overflows the stock<00:22:38.039> there<00:22:38.159> is<00:22:38.679> uh<00:22:39.120> possibility<00:22:39.640> of 00:22:39.789 --> 00:22:39.799 align:start position:0% stock there is uh possibility of 00:22:39.799 --> 00:22:41.990 align:start position:0% stock there is uh possibility of overflows<00:22:40.360> but<00:22:40.520> not<00:22:40.679> underflows<00:22:41.520> that's<00:22:41.840> the 00:22:41.990 --> 00:22:42.000 align:start position:0% overflows but not underflows that's the 00:22:42.000 --> 00:22:45.149 align:start position:0% overflows but not underflows that's the answer<00:22:42.400> yeah<00:22:42.799> um<00:22:43.799> underflows<00:22:44.360> are<00:22:44.520> completely 00:22:45.149 --> 00:22:45.159 align:start position:0% answer yeah um underflows are completely 00:22:45.159 --> 00:22:47.470 align:start position:0% answer yeah um underflows are completely eliminated<00:22:45.760> thanks<00:22:46.000> to<00:22:46.240> static<00:22:46.840> validation 00:22:47.470 --> 00:22:47.480 align:start position:0% eliminated thanks to static validation 00:22:47.480 --> 00:22:51.549 align:start position:0% eliminated thanks to static validation at<00:22:47.760> at<00:22:48.240> uh<00:22:49.000> deployment<00:22:49.559> time<00:22:49.919> and<00:22:50.559> overflows 00:22:51.549 --> 00:22:51.559 align:start position:0% at at uh deployment time and overflows 00:22:51.559 --> 00:22:54.029 align:start position:0% at at uh deployment time and overflows still<00:22:51.840> can<00:22:52.080> happen<00:22:52.760> but<00:22:53.320> uh<00:22:53.440> we<00:22:53.600> do<00:22:53.760> not<00:22:53.919> need 00:22:54.029 --> 00:22:54.039 align:start position:0% still can happen but uh we do not need 00:22:54.039 --> 00:22:56.470 align:start position:0% still can happen but uh we do not need to<00:22:54.159> check<00:22:54.400> them<00:22:54.520> at<00:22:54.640> every<00:22:54.799> instruction<00:22:55.279> as<00:22:55.480> I 00:22:56.470 --> 00:22:56.480 align:start position:0% to check them at every instruction as I 00:22:56.480 --> 00:23:01.830 align:start position:0% to check them at every instruction as I as<00:22:56.559> I<00:22:56.760> said<00:22:57.360> mhm<00:22:58.320> uh<00:22:58.840> uh<00:22:59.400> and<00:23:00.360> um<00:23:01.360> the<00:23:01.520> next 00:23:01.830 --> 00:23:01.840 align:start position:0% as I said mhm uh uh and um the next 00:23:01.840 --> 00:23:07.070 align:start position:0% as I said mhm uh uh and um the next question<00:23:02.279> is<00:23:02.799> uh<00:23:03.400> if<00:23:03.919> St<00:23:04.919> validation<00:23:05.640> makes<00:23:06.320> uh 00:23:07.070 --> 00:23:07.080 align:start position:0% question is uh if St validation makes uh 00:23:07.080 --> 00:23:10.470 align:start position:0% question is uh if St validation makes uh ZK<00:23:07.600> cross<00:23:07.919> compilation<00:23:08.679> or<00:23:09.000> ZK<00:23:10.000> Trace 00:23:10.470 --> 00:23:10.480 align:start position:0% ZK cross compilation or ZK Trace 00:23:10.480 --> 00:23:13.470 align:start position:0% ZK cross compilation or ZK Trace aromatization<00:23:11.480> easier<00:23:11.840> or 00:23:13.470 --> 00:23:13.480 align:start position:0% aromatization easier or 00:23:13.480 --> 00:23:16.430 align:start position:0% aromatization easier or harder<00:23:14.480> it<00:23:14.840> definitely<00:23:15.279> makes<00:23:15.480> it<00:23:15.640> easier<00:23:16.200> if 00:23:16.430 --> 00:23:16.440 align:start position:0% harder it definitely makes it easier if 00:23:16.440 --> 00:23:20.430 align:start position:0% harder it definitely makes it easier if in<00:23:16.640> case<00:23:17.240> this<00:23:17.520> ZK<00:23:17.919> compilation<00:23:18.600> targets<00:23:19.440> eof 00:23:20.430 --> 00:23:20.440 align:start position:0% in case this ZK compilation targets eof 00:23:20.440 --> 00:23:22.909 align:start position:0% in case this ZK compilation targets eof only<00:23:20.760> eof<00:23:21.159> and<00:23:21.559> does<00:23:21.760> not<00:23:21.960> try<00:23:22.159> to<00:23:22.480> support 00:23:22.909 --> 00:23:22.919 align:start position:0% only eof and does not try to support 00:23:22.919 --> 00:23:25.990 align:start position:0% only eof and does not try to support Legacy<00:23:23.320> 2<00:23:23.600> in<00:23:23.760> case<00:23:24.240> it<00:23:24.360> is<00:23:25.039> ZK<00:23:25.559> system<00:23:25.880> that 00:23:25.990 --> 00:23:26.000 align:start position:0% Legacy 2 in case it is ZK system that 00:23:26.000 --> 00:23:28.149 align:start position:0% Legacy 2 in case it is ZK system that tries<00:23:26.240> to<00:23:26.400> support<00:23:26.799> both<00:23:27.200> Legacy<00:23:27.559> execution 00:23:28.149 --> 00:23:28.159 align:start position:0% tries to support both Legacy execution 00:23:28.159 --> 00:23:31.190 align:start position:0% tries to support both Legacy execution and<00:23:28.880> UF<00:23:29.320> execution<00:23:29.919> then<00:23:30.600> it<00:23:30.760> has<00:23:30.919> to 00:23:31.190 --> 00:23:31.200 align:start position:0% and UF execution then it has to 00:23:31.200 --> 00:23:32.950 align:start position:0% and UF execution then it has to basically<00:23:31.559> support<00:23:31.919> two<00:23:32.080> different<00:23:32.400> systems 00:23:32.950 --> 00:23:32.960 align:start position:0% basically support two different systems 00:23:32.960 --> 00:23:35.870 align:start position:0% basically support two different systems that<00:23:33.120> is<00:23:33.679> big<00:23:33.919> pain<00:23:34.159> I<00:23:34.320> guess<00:23:34.600> so<00:23:35.440> it's 00:23:35.870 --> 00:23:35.880 align:start position:0% that is big pain I guess so it's 00:23:35.880 --> 00:23:39.590 align:start position:0% that is big pain I guess so it's generally<00:23:36.640> much<00:23:37.640> better<00:23:38.039> idea<00:23:38.400> to<00:23:38.600> support<00:23:39.000> EF 00:23:39.590 --> 00:23:39.600 align:start position:0% generally much better idea to support EF 00:23:39.600 --> 00:23:42.350 align:start position:0% generally much better idea to support EF for<00:23:39.840> them<00:23:40.200> and<00:23:40.720> uh 00:23:42.350 --> 00:23:42.360 align:start position:0% for them and uh 00:23:42.360 --> 00:23:46.430 align:start position:0% for them and uh then<00:23:43.360> thanks<00:23:43.760> to<00:23:44.760> code<00:23:45.200> validation<00:23:46.200> and 00:23:46.430 --> 00:23:46.440 align:start position:0% then thanks to code validation and 00:23:46.440 --> 00:23:49.110 align:start position:0% then thanks to code validation and thanks<00:23:46.679> to<00:23:47.480> uh<00:23:47.600> deleting<00:23:48.080> code<00:23:48.320> observability 00:23:49.110 --> 00:23:49.120 align:start position:0% thanks to uh deleting code observability 00:23:49.120 --> 00:23:52.029 align:start position:0% thanks to uh deleting code observability ZK<00:23:49.799> compilation<00:23:50.480> becomes<00:23:51.159> much<00:23:51.360> easier 00:23:52.029 --> 00:23:52.039 align:start position:0% ZK compilation becomes much easier 00:23:52.039 --> 00:23:54.230 align:start position:0% ZK compilation becomes much easier that's<00:23:52.640> at<00:23:52.760> least<00:23:53.039> the<00:23:53.200> theory<00:23:53.679> and<00:23:54.120> yeah 00:23:54.230 --> 00:23:54.240 align:start position:0% that's at least the theory and yeah 00:23:54.240 --> 00:23:55.830 align:start position:0% that's at least the theory and yeah we'll<00:23:54.400> see<00:23:54.600> how<00:23:54.760> this<00:23:54.919> works 00:23:55.830 --> 00:23:55.840 align:start position:0% we'll see how this works 00:23:55.840 --> 00:24:00.590 align:start position:0% we'll see how this works out<00:23:56.840> okay<00:23:57.080> and<00:23:57.600> uh<00:23:57.960> I<00:23:58.080> guess<00:23:58.440> last<00:23:58.679> question<00:23:59.640> uh 00:24:00.590 --> 00:24:00.600 align:start position:0% out okay and uh I guess last question uh 00:24:00.600 --> 00:24:03.310 align:start position:0% out okay and uh I guess last question uh will<00:24:01.440> gas<00:24:01.720> fee<00:24:02.240> reduce<00:24:02.880> after<00:24:03.120> the 00:24:03.310 --> 00:24:03.320 align:start position:0% will gas fee reduce after the 00:24:03.320 --> 00:24:05.510 align:start position:0% will gas fee reduce after the optimization<00:24:04.200> and<00:24:04.400> if<00:24:04.559> so<00:24:04.799> how<00:24:05.000> much<00:24:05.440> there 00:24:05.510 --> 00:24:05.520 align:start position:0% optimization and if so how much there 00:24:05.520 --> 00:24:08.470 align:start position:0% optimization and if so how much there was<00:24:05.640> no<00:24:05.840> exact<00:24:06.080> plans<00:24:06.400> to<00:24:06.559> reduce<00:24:07.000> gas<00:24:07.640> but<00:24:08.279> uh 00:24:08.470 --> 00:24:08.480 align:start position:0% was no exact plans to reduce gas but uh 00:24:08.480 --> 00:24:12.549 align:start position:0% was no exact plans to reduce gas but uh we<00:24:08.880> definitely<00:24:09.360> will<00:24:09.919> see<00:24:11.039> some<00:24:12.039> uh 00:24:12.549 --> 00:24:12.559 align:start position:0% we definitely will see some uh 00:24:12.559 --> 00:24:15.630 align:start position:0% we definitely will see some uh improvements<00:24:13.120> in<00:24:14.039> in<00:24:14.400> in<00:24:14.640> execution<00:24:15.080> time<00:24:15.480> and 00:24:15.630 --> 00:24:15.640 align:start position:0% improvements in in in execution time and 00:24:15.640 --> 00:24:17.070 align:start position:0% improvements in in in execution time and this<00:24:15.799> might<00:24:16.000> lead<00:24:16.200> to<00:24:16.279> some<00:24:16.440> optimizations<00:24:16.960> in 00:24:17.070 --> 00:24:17.080 align:start position:0% this might lead to some optimizations in 00:24:17.080 --> 00:24:17.789 align:start position:0% this might lead to some optimizations in the 00:24:17.789 --> 00:24:17.799 align:start position:0% the 00:24:17.799 --> 00:24:21.310 align:start position:0% the future<00:24:18.799> uh<00:24:19.559> there<00:24:19.720> will<00:24:19.919> be<00:24:20.360> gas<00:24:20.760> savings 00:24:21.310 --> 00:24:21.320 align:start position:0% future uh there will be gas savings 00:24:21.320 --> 00:24:23.269 align:start position:0% future uh there will be gas savings thanks<00:24:21.600> to<00:24:22.000> better<00:24:22.400> stack<00:24:22.640> management<00:24:23.159> this 00:24:23.269 --> 00:24:23.279 align:start position:0% thanks to better stack management this 00:24:23.279 --> 00:24:26.070 align:start position:0% thanks to better stack management this is<00:24:23.559> like<00:24:23.720> not<00:24:24.520> uh<00:24:24.720> specifically<00:24:25.159> related<00:24:25.520> to 00:24:26.070 --> 00:24:26.080 align:start position:0% is like not uh specifically related to 00:24:26.080 --> 00:24:28.110 align:start position:0% is like not uh specifically related to validation<00:24:26.760> but<00:24:27.039> rather<00:24:27.320> to<00:24:27.480> a<00:24:27.640> better<00:24:27.960> just 00:24:28.110 --> 00:24:28.120 align:start position:0% validation but rather to a better just 00:24:28.120 --> 00:24:29.710 align:start position:0% validation but rather to a better just better<00:24:28.399> instruction<00:24:29.039> instructions<00:24:29.520> to 00:24:29.710 --> 00:24:29.720 align:start position:0% better instruction instructions to 00:24:29.720 --> 00:24:32.190 align:start position:0% better instruction instructions to handle<00:24:30.320> values<00:24:30.640> on<00:24:30.880> stack<00:24:31.480> uh<00:24:31.799> we<00:24:31.919> have<00:24:32.080> now 00:24:32.190 --> 00:24:32.200 align:start position:0% handle values on stack uh we have now 00:24:32.200 --> 00:24:34.590 align:start position:0% handle values on stack uh we have now Swap<00:24:32.520> and<00:24:32.720> d<00:24:32.919> and<00:24:33.200> and<00:24:33.520> exchange<00:24:34.080> and<00:24:34.320> all 00:24:34.590 --> 00:24:34.600 align:start position:0% Swap and d and and exchange and all 00:24:34.600 --> 00:24:37.470 align:start position:0% Swap and d and and exchange and all these<00:24:35.600> uh<00:24:35.880> simplifies<00:24:36.520> life<00:24:36.679> for<00:24:36.840> compilers 00:24:37.470 --> 00:24:37.480 align:start position:0% these uh simplifies life for compilers 00:24:37.480 --> 00:24:39.710 align:start position:0% these uh simplifies life for compilers and<00:24:37.919> in<00:24:38.039> the<00:24:38.159> end<00:24:38.480> reduces<00:24:38.960> gas<00:24:39.200> consumed<00:24:39.559> for 00:24:39.710 --> 00:24:39.720 align:start position:0% and in the end reduces gas consumed for 00:24:39.720 --> 00:24:40.750 align:start position:0% and in the end reduces gas consumed for entire 00:24:40.750 --> 00:24:40.760 align:start position:0% entire 00:24:40.760 --> 00:24:44.389 align:start position:0% entire execution<00:24:41.760> great<00:24:42.080> how<00:24:42.200> much<00:24:42.360> can<00:24:42.480> I<00:24:43.159> say<00:24:44.159> uh 00:24:44.389 --> 00:24:44.399 align:start position:0% execution great how much can I say uh 00:24:44.399 --> 00:24:48.000 align:start position:0% execution great how much can I say uh let's<00:24:44.679> thanks<00:24:45.279> um