Re: [PATCHv3] x86/selftests: add clobbers for int80 on x86_64

[hpa]

On February 13, 2017 11:06:04 AM PST, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>On Mon, Feb 13, 2017 at 2:13 AM, Dmitry Safonov
><dsafonov@xxxxxxxxxxxxx> 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.  Also, as notted by Andy - removed unneeded clobber
>> for flags in int 0x80 inline asm.
>
>Acked-by: Andy Lutomirski <luto@xxxxxxxxxx>
>
>Although these days we could preserve these regs in the kernel at the
>cost of (I think) 4 bytes of text and zero runtime overhead.
>
>--Andy

If we can do so that cheaply I think we should.
-- 
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