Messages in this thread | | | Date | Fri, 19 Apr 2019 17:13:21 -0400 (EDT) | From | Mathieu Desnoyers <> | Subject | Re: [tip:core/rseq] rseq/selftests/x86: Work around bogus gcc-8 optimisation |
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----- On Apr 19, 2019, at 2:53 PM, Linus Torvalds torvalds@linux-foundation.org wrote:
> On Fri, Apr 19, 2019 at 11:46 AM tip-bot for Mathieu Desnoyers > <tipbot@zytor.com> wrote: >> >> rseq/selftests/x86: Work around bogus gcc-8 optimisation >> >> At least the following versions of gcc-8: >> >> - gcc version 8.0.1 20180414 (experimental) [trunk revision 259383] (Ubuntu >> 8-20180414-1ubuntu2) >> - gcc 8.2.0-7ubuntu1 (Ubuntu 18.10 (Cosmic)), >> >> generate broken assembler with asm goto that have a thread-local storage >> "m" input operand on both x86-32 and x86-64. For instance: > > Is there a gcc bugzilla for this? Shouldn't that be mentioned here?
My google-fu did not find any match, so I don't think so. I'll open one shortly.
> > Also, we use "asm goto" together with "m" all the time in the kernel. > In fact, it's the most common case, with the RMWcc ops being generated > with that. I realize that we don't use the gcc thread-local storage > for them (we often do use our *own* thread-local storage), but it > would be good to have that gcc bugzilla to see why it can only affect > those user level "__thread" cases.
Indeed, it would be good to investigate and understand all problematic scenarios triggering this bug.
Thanks,
Mathieu
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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