Messages in this thread | | | Subject | Re: [PATCH] x86/selftests: add clobbers for int80 on x86_64 | From | Dmitry Safonov <> | Date | Fri, 10 Feb 2017 19:28:59 +0300 |
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On 02/10/2017 07:13 PM, Andy Lutomirski wrote: > 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). >
Well, that was my initial attempt: I've defined it as: +# define INT80_CLOBBERS , "r8", "r9", "r10", "r11"
But that hanging comma looks awful, so I added "flags" there. And if I do define it without coma and leave it in asm statement, 32-bit version would be unhappy. So, I found that it's easier to define it with flags included.
-- Dmitry
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