Re: [PATCH] x86/selftests: add clobbers for int80 on x86_64

From	Andy Lutomirski <luto@amacapital.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH] x86/selftests: add clobbers for int80 on x86_64
Date	2017-02-10 17:30 +0100
Message-ID	<t9mf7-5Nv-3@gated-at.bofh.it> (permalink)
References	<t9mf7-5Nv-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Fri, Feb 10, 2017 at 3:52 AM, Dmitry Safonov <dsafonov@virtuozzo.com> wrote:
> Kernel erases R8..R11 registers prior returning to userspace
> from int80: https://lkml.org/lkml/2009/10/1/164
>
> GCC can reuse this registers and doesn't expect them to change
> during syscall invocation. I met this kind of bug in CRIU once
> gcc 6.1 and clang stored local variables in those registers
> and the kernel zerofied them during syscall:
> https://github.com/xemul/criu/commit/990d33f1a1cdd17bca6c2eb059ab3be2564f7fa2
>
> By that reason I suggest to add those registers to clobbers
> in selftests.

Seems reasonable, but presumably INT80_CLOBBERS should be defined the
same way in all the tests.  IOW, if the "flags" clobber is actually
needed, it should be "flags", INT80_CLOBBERS (possibly without the
comma if it's problematic).

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Re: [PATCH] x86/selftests: add clobbers for int80 on x86_64 Andy Lutomirski <luto@amacapital.net> - 2017-02-10 17:30 +0100
  Re: [PATCH] x86/selftests: add clobbers for int80 on x86_64 Andy Lutomirski <luto@amacapital.net> - 2017-02-10 17:50 +0100

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