1 00:00:00,150 --> 00:00:01,410 ‫Hello and welcome, everybody. 2 00:00:02,250 --> 00:00:05,580 ‫There's a small bug with the bass points, reviews of processes. 3 00:00:06,360 --> 00:00:16,110 ‫So essentially I just want us to go to blank and blank dot C and ignore that test program. 4 00:00:16,110 --> 00:00:17,720 ‫I made that to find the bug. 5 00:00:17,740 --> 00:00:18,090 ‫Great. 6 00:00:18,780 --> 00:00:19,980 ‫So you guys won't have that. 7 00:00:20,670 --> 00:00:24,220 ‫And here I just want you to go for instar equals zero. 8 00:00:24,660 --> 00:00:26,010 ‫I below a million. 9 00:00:27,730 --> 00:00:33,220 ‫I plus plus and we're just going to go here and we're going to make clean Bill LSH. 10 00:00:34,090 --> 00:00:35,980 ‫And I want to show you what happens. 11 00:00:37,070 --> 00:00:38,350 ‫OK, we're going to run that. 12 00:00:38,920 --> 00:00:43,810 ‫You'll see ABC testing, ABC testing, and then you'll see no processes to switch to. 13 00:00:45,250 --> 00:00:47,140 ‫So this is a nasty bug. 14 00:00:47,140 --> 00:00:48,130 ‫What is happening? 15 00:00:48,580 --> 00:00:54,790 ‫Essentially, our follow up is using the base pointer and the base point of value is corrupted. 16 00:00:55,510 --> 00:00:58,510 ‫Now, where does the base point of value get corrupted? 17 00:00:58,540 --> 00:01:01,180 ‫Well, if we go to task and test out, see? 18 00:01:02,350 --> 00:01:05,710 ‫And here we'll see test, switch, test for term. 19 00:01:06,370 --> 00:01:09,490 ‫The bug is in tax returns are good to test it, I assume. 20 00:01:10,090 --> 00:01:11,770 ‫And you will see. 21 00:01:14,590 --> 00:01:22,300 ‫Tax return, buy here now everything, and he is correct, except when we call the general-purpose registers. 22 00:01:22,750 --> 00:01:25,290 ‫So in the general purpose registers, what do we do? 23 00:01:25,300 --> 00:01:30,850 ‫We restore all of the registers back to the ones that were in the register structure that we passed 24 00:01:30,850 --> 00:01:31,990 ‫this assembly function. 25 00:01:32,260 --> 00:01:33,350 ‫That's perfect, correct? 26 00:01:33,370 --> 00:01:33,670 ‫Right. 27 00:01:34,000 --> 00:01:34,870 ‫We go through them all. 28 00:01:34,870 --> 00:01:39,160 ‫We restore EDIR, CBP, FedEx, X, and so on. 29 00:01:39,610 --> 00:01:41,890 ‫But look what we do here on line 62. 30 00:01:42,580 --> 00:01:47,260 ‫We pop the base pointer that we saved because here we push the base pointer. 31 00:01:47,740 --> 00:01:53,260 ‫Here we popped off the base pointer, overwriting the restored base pointer value. 32 00:01:53,680 --> 00:02:01,480 ‫And that is what leads to that nasty bug where accessing the stack is done incorrectly. 33 00:02:02,110 --> 00:02:04,270 ‫So how do we fix this? 34 00:02:05,580 --> 00:02:05,890 ‫Wow. 35 00:02:06,150 --> 00:02:12,570 ‫We get rid of the pop MBP and we change it to add E.S.P fall, which will basically restore the stack 36 00:02:12,570 --> 00:02:15,630 ‫pointer back to where it should be, whether it's home addresses. 37 00:02:16,050 --> 00:02:19,440 ‫But it will not pop into the base pointer. 38 00:02:20,220 --> 00:02:20,590 ‫OK. 39 00:02:20,610 --> 00:02:25,890 ‫And once you've done that, if we now go back to the terminal and we make may clean bill that I think 40 00:02:26,430 --> 00:02:29,220 ‫we should see that bug is now resolved. 41 00:02:31,310 --> 00:02:33,920 ‫And there we go, everything works as expected. 42 00:02:34,730 --> 00:02:40,190 ‫Now, that boat took a long time to find it really was a needle in a haystack. 43 00:02:40,220 --> 00:02:42,890 ‫You saw how how easy that mistake was. 44 00:02:42,890 --> 00:02:43,190 ‫Right. 45 00:02:44,630 --> 00:02:51,020 ‫But, you know, Colonel, development is all about solving problems and and building systems. 46 00:02:51,020 --> 00:02:56,000 ‫And, you know, even Microsoft are releasing bug fixes every few months. 47 00:02:56,810 --> 00:02:58,460 ‫Nobody's immune from this. 48 00:02:58,850 --> 00:03:02,390 ‫So I appreciate your patience with some of these bug fixes. 49 00:03:02,840 --> 00:03:08,350 ‫But I will always fix any bug that is found in my work. 50 00:03:08,360 --> 00:03:10,880 ‫And I appreciate your patience. 51 00:03:11,540 --> 00:03:17,210 ‫And yes, so very easy bug to fix was a very hard bug to find. 52 00:03:17,990 --> 00:03:19,280 ‫OK, take care of everyone.