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

From: Andy Lutomirski
Date: Fri Feb 10 2017 - 11:21:20 EST

On Fri, Feb 10, 2017 at 3:52 AM, Dmitry Safonov <dsafonov@xxxxxxxxxxxxx> wrote:
> Kernel erases R8..R11 registers prior returning to userspace
> from int80:
> 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:
> 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).