I found a bug in Intel Skylake processors • Hacker News Board

Re: I found a bug in Intel Skylake processors

#91

Post by justin66 » Mon, Jul 03, 2017, 10:40 PM UTC

tom_mellior wrote: post #89

justin66 wrote: post #86

Earlier quoted context omitted.

Since we're communicating via rhetorical questions, are you asserting that it's literally impossible to contact Intel support with a defect, or merely tedious? Does it become easier or more difficult if you have a reproducible test case and the sort of connections a prominent FP compiler person has?

I'm trusting the account of the prominent FP compiler person who had a test case and wrote in the linked article that he found no way to submit the issue. You're the one saying this cannot be true, but you're not saying why you think so.

1. That's not what I'm saying

2. That's not what he wrote

Re: I found a bug in Intel Skylake processors

#92

Post by justin66 » Mon, Jul 03, 2017, 10:43 PM UTC

jacquesm wrote: post #90

justin66 wrote: post #87

Earlier quoted context omitted.

I am shocked by this attitude. Maybe I shouldn't be, and I'll certainly give this all some thought. There's at least one obvious error in your statement: if an inconvenienced user's bug report results in less downtime for other users, it is a "gift" to other users, as well as a "gift" to the vendor. But it says something about our profession if we regard putting flags down to mark the landmines we find a mere courtes…

Well, guess what: you're as entitled to your opinion as I am to mine. But just like a user has no obligation to 'mark the landmines' for vendors they also have no such obligation towards other users. They do have a right to receiving bug free software in the first place, alas our industry is utterly incapable of doing so which has lowered our expectations to the point where you feel that we have an actual obligation…

> You're just a small step away from making it an obligation rather than an optional thing for users to report bugs, the only difference is that for you the obligation is a moral one rather than a legal one.

I'd argue that a person does have that obligation in some circumstances, yes. And yes, I am thinking in moral rather than legal terms. The legal picture is pretty far outside my expertise, and the professional ethics of software engineering (which would in turn inform the legal picture) seems to be woefully opt-in. As you say, 'moving fast and breaking shit,' perpetual beta test mode, etc. So I'd put the legal stuff aside for now.

For me, the key is that "user" is a deceptive term here. A mere user cannot point to a small piece inside a much larger machine and say "that will blow up occasionally, and I know exactly when." We are talking about engineers. Or at least, I was thinking of the professional obligations of engineers - on the user side of the fence and the vendor side of the fence - and that was informing my comments.

> Keep in mind that users have their own work to do, are not on the payroll of the vendors usually have forked over cold hard cash in order to be able to use the code (ok, not in the case of open source) and tend to be less knowledgeable about this stuff than the vendors.

Yeah, and I don't think I disagree with you in the "user" case. I really think a software engineer finding a CPU bug is a different case. It seems me that if we're in possession of knowledge of something as serious and wide-reaching as a CPU bug, we have a reproducible test case, and we don't do anything with it (I mean, at least a tweet or something, for the love of God) we are part of the problem with our profession.

Re: I found a bug in Intel Skylake processors

#93

Post by pcwalton » Mon, Jul 03, 2017, 10:48 PM UTC

userbinator wrote: post #46

raverbashing wrote: post #3

GCC generates code that's smaller but it isn't optimal, because of the potential for partial register stalls (and just overall register renaming issues) It's of course not wrong, but using AH when you're dealing with RAX is a weird anachronism Clang does the obvious, correct thing.

"smaller but not optimal" is not really true. It depends on what you're optimising for. In my experience, optimising for size overall, and then speed in the really performance-critical parts (with some expected expansion), gives the best results. Even the non-performance-critical code will have a noticeable effect if its larger size causes more cache misses. Making use of the "partial registers" (I see them more as s…

AH/BH/CH/DH are so seldom useful that it's not really worth adding support for using them to the compiler. They only exist for 4 of the 16 registers, and they only let you address one random byte of the 8 bytes in that register. You get a bit slower code and a more complicated register allocator in order to save, what, a few bytes in the entire program?

Re: I found a bug in Intel Skylake processors

#94

Post by jacquesm » Mon, Jul 03, 2017, 10:51 PM UTC

justin66 wrote: post #92

jacquesm wrote: post #90

Earlier quoted context omitted.

Well, guess what: you're as entitled to your opinion as I am to mine. But just like a user has no obligation to 'mark the landmines' for vendors they also have no such obligation towards other users. They do have a right to receiving bug free software in the first place, alas our industry is utterly incapable of doing so which has lowered our expectations to the point where you feel that we have an actual obligation…

> You're just a small step away from making it an obligation rather than an optional thing for users to report bugs, the only difference is that for you the obligation is a moral one rather than a legal one. I'd argue that a person does have that obligation in some circumstances, yes. And yes, I am thinking in moral rather than legal terms. The legal picture is pretty far outside my expertise, and the professional et…

I'm on board with a reporting duty if such a thing will always result in:

(1) a payment from the vendor to the reporter compensating them for time and effort spent at getting the bug to be reproduced

and, crucially,

(2) a requirement for all vendors of software and hardware to timely respond to bug reports and to have a standardized reporting process.

In that case I can see how such a shared responsibility would work, but as it is the companies get the benefits and the users get the hardship with a good portion of reported bugs (sometimes including a solution) that go unfixed, that's not a fair situation.

Case in point: I've reported quite a few bugs to vendors over the years but I've stopped doing it because in general vendors simply don't care, most of the time bug reports seem to result in a 'wont fix' or 'here is a paid upgrade for you with your fix in it'.

Re: I found a bug in Intel Skylake processors

#95

Post by justin66 » Tue, Jul 04, 2017, 3:35 AM UTC

jacquesm wrote: post #94

justin66 wrote: post #92

Earlier quoted context omitted.

> You're just a small step away from making it an obligation rather than an optional thing for users to report bugs, the only difference is that for you the obligation is a moral one rather than a legal one. I'd argue that a person does have that obligation in some circumstances, yes. And yes, I am thinking in moral rather than legal terms. The legal picture is pretty far outside my expertise, and the professional et…

I'm on board with a reporting duty if such a thing will always result in: (1) a payment from the vendor to the reporter compensating them for time and effort spent at getting the bug to be reproduced and, crucially, (2) a requirement for all vendors of software and hardware to timely respond to bug reports and to have a standardized reporting process. In that case I can see how such a shared responsibility would work…

The security guys seem to be converging on a way of managing these - the compensation of the person reporting the bug and the factors motivating vendors to respond to the bug report in a timely fashion or suffer consequences - with bug bounties. Intel should make it easy to report this stuff, but if everyone understood that finding something genuinely interesting resulted in a serious payday, nobody would skip making the call.

The difference between something like Google's bug bounty (capped at over $30k, I think) and a hypothetical bounty for Intel is, well, Intel has a lot more at stake. It's honestly strange that they don't have something in place already. Something like Skylake costs on the order of billions to get out there. It's cool that this Skylake bug was fixable via microcode, but the Pentium FPU bug back in the day cost them half a billion dollars. If such a bug exists, that is the kind of thing Intel should want to have reported as soon as humanly possible. Even the reputational damage they take from something milder like the Skylake bug would justify a bounty system with very serious payouts.

Re: I found a bug in Intel Skylake processors

#96

Post by AgentME » Tue, Jul 04, 2017, 6:37 AM UTC

jacquesm wrote: post #82

ihnorton wrote: post #13

> I worked from the executable provided by SIOU, first interactively under GDB (but it nearly drove me crazy, as I had to wait sometimes one hour to trigger the crash again), then using a little OCaml script that ran the program 1000 times and saved the core dumps produced at every crash. rr can often be a time-saver in situations by providing deterministic replays up to the point of a crash, whereas coredump analysi…

How will emulation trigger a hardware bug?

rr doesn't do any emulation. It records the inputs to a program so that it could be run again deterministically the same way again. However it doesn't actually run code as multi-threaded so it wouldn't be a help here.

Re: I found a bug in Intel Skylake processors

#97

Post by testfailure » Tue, Jul 04, 2017, 11:08 AM UTC

ihnorton wrote: post #13

> I worked from the executable provided by SIOU, first interactively under GDB (but it nearly drove me crazy, as I had to wait sometimes one hour to trigger the crash again), then using a little OCaml script that ran the program 1000 times and saved the core dumps produced at every crash. rr can often be a time-saver in situations by providing deterministic replays up to the point of a crash, whereas coredump analysi…

Replaying the recorded code under either rr or UndoDB would have revealed that something odd was going on in the CPU when the recording replayed differently depending on whether HT was enabled. Obviously finding this would have required that the tester replayed the recording multiple times with and without HT enabled

Re: I found a bug in Intel Skylake processors

#98

Post by gimmick73 » Tue, Jul 04, 2017, 11:27 AM UTC

j_jochem wrote: post #37

gfiorav wrote: post #9

Earlier quoted context omitted.

I'd say no, you likely won't run into trouble because of this

This is subjective and very anecdotal, so take with a heap of salt: My 2016 Skylake MBP used to crash very regularly when waking it up from suspend (sometimes multiple times a day). When I first heard about this issue a week ago, I used XCode Instruments to disable Hypterthreading. I have not observed a single crash since.

Also anecdotal but I am experiencing no crashes with HT off on my 2016 MBPr. Be sure to turn HT off after a sleep/wake cycle as it gets reset each time.

Re: I found a bug in Intel Skylake processors

#99

Post by j_jochem » Tue, Jul 04, 2017, 1:27 PM UTC

gimmick73 wrote: post #98

j_jochem wrote: post #37

Earlier quoted context omitted.

This is subjective and very anecdotal, so take with a heap of salt: My 2016 Skylake MBP used to crash very regularly when waking it up from suspend (sometimes multiple times a day). When I first heard about this issue a week ago, I used XCode Instruments to disable Hypterthreading. I have not observed a single crash since.

Also anecdotal but I am experiencing no crashes with HT off on my 2016 MBPr. Be sure to turn HT off after a sleep/wake cycle as it gets reset each time.

Did you get a lot of crashes before?

Re: I found a bug in Intel Skylake processors

#100

Post by johnbellone » Tue, Jul 04, 2017, 1:28 PM UTC

justin66 wrote: post #87

jacquesm wrote: post #81

Earlier quoted context omitted.

Bug reports are gifts from inconvenienced users to vendors who have just done free work on the vendors behalf. There is absolutely no obligation on the part of a user to report bugs.

I am shocked by this attitude. Maybe I shouldn't be, and I'll certainly give this all some thought. There's at least one obvious error in your statement: if an inconvenienced user's bug report results in less downtime for other users, it is a "gift" to other users, as well as a "gift" to the vendor. But it says something about our profession if we regard putting flags down to mark the landmines we find a mere courtes…

I am genuinely wondering why you think this way? I do not expect my users to report failures. If they do I am more than pleased (not sure I would call it a "gift") because it shows that my product is good enough that they won't just leave out of frustration.

As technologists, we develop tools and services to capture bugs (both server side and client) so that we gain more insight into how our product operates. A user that takes time to give a well crafted bug report is rare. Most of the time it tends to be legitimate gripe that a feature isn't working.

Update: After writing I am re-reading your comment and now thinking we are on same page.