Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] linux-user: ppc64: don't use volatile register during safe_syscall

[David Gibson]

On Thu, Jul 26, 2018 at 10:20:11PM -0700, Richard Henderson wrote:
> On 07/26/2018 08:13 PM, David Gibson wrote:
> > On Thu, Jul 26, 2018 at 01:56:19PM +0530, Shivaprasad G Bhat wrote:
> >> r11 is a volatile register on PPC as per calling conventions.
> >> The safe_syscall code uses it to check if the signal_pending
> >> is set during the safe_syscall. When a syscall is interrupted
> >> on return from signal handling, the r11 might be corrupted
> >> before we retry the syscall leading to a crash. The registers
> >> r0-r13 are not to be used here as they have
> >> volatile/designated/reserved usages. Change the code to use
> >> r14 which is non-volatile and is appropriate for local use in
> >> safe_syscall.
> >>
> >> Steps to reproduce:
> >> On PPC host, issue `qemu-x86_64 /usr/bin/cc -E -`
> >> Attempt Ctrl-C, the issue is reproduced.
> >>
> >> Reference:
> >> https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi-1.9.html#REG
> >>
> >> Signed-off-by: Shivaprasad G Bhat <address@hidden>
> >> Tested-by: Laurent Vivier <address@hidden>
> >> Reviewed-by: Laurent Vivier <address@hidden>
> > 
> > Applied to ppc-for-3.0.
> 
> No please!  r14 is a call-saved register and needs saving before
> clobbering.

Oops, pulled out now.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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