Messages in this thread | | | Subject | Re: [PATCH] x86/selftests: add clobbers for int80 on x86_64 | From | Dmitry Safonov <> | Date | Fri, 10 Feb 2017 20:11:46 +0300 |
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On 02/10/2017 07:45 PM, Andy Lutomirski wrote: > On Fri, Feb 10, 2017 at 8:28 AM, Dmitry Safonov <dsafonov@virtuozzo.com> wrote: >> 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. >> > > Woudl the right answer be to get rid of "flags" in the test where it > appears? I'm not sure it's needed in the first place. >
I think it can live without it. But I didn't want to change it in the same patch and wasn't sure if I fail to see the reason for it. So, I'll resend with flags removing, thanks.
-- Dmitry
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