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

[Laurent Vivier <laurent@vivier.eu>]

Le 26/07/2018 à 08:48, Shivaprasad G Bhat a écrit :
> 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.
> 
> Signed-off-by: Shivaprasad G Bhat <sbhat@linux.vnet.ibm.com>
> ---
> Steps to reproduce:
> On PPC host, issue `qemu-ppc64le /usr/bin/cc -E -`
> Attempt Ctrl-C, the issue is reproduced.
> 
> Reference:
> https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi-1.9.html#REG

I think these comments should be included in the commit message.
Using the example of qemu-x86_64 on ppc64 would be less ambiguous.

I've tested on ppc64:

    qemu-x86_64 /usr/bin/cc -E -

Tested-by: Laurent Vivier <laurent@vivier.eu>

>  linux-user/host/ppc64/safe-syscall.inc.S |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 

Reviewed-by: Laurent Vivier <laurent@vivier.eu>

Thanks,
Laurent