RE: [PATCH] x86/asm: Don't use rbp as temp register in csum_partial_copy_generic()

From: David Laight
Date: Thu May 04 2017 - 12:00:16 EST

From: Josh Poimboeuf
> Sent: 04 May 2017 15:52
> Andrey Konovalov reported the following warning while fuzzing the kernel
> with syzkaller:
> WARNING: kernel stack regs at ffff8800686869f8 in a.out:4933 has bad 'bp' value c3fc855a10167ec0
> The unwinder dump revealed that rbp had a bad value when an interrupt
> occurred in csum_partial_copy_generic().
> That function saves rbp on the stack and then overwrites it, using it as
> a scratch register. That's problematic because it breaks stack traces
> if an interrupt occurs in the middle of the function.

Does gcc guarantee not to use bp as a scratch register in leaf functions?