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

[David Gibson <david@gibson.dropbear.id.au>]

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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 <sbhat@linux.vnet.ibm.com>
> Tested-by: Laurent Vivier <laurent@vivier.eu>
> Reviewed-by: Laurent Vivier <laurent@vivier.eu>

Applied to ppc-for-3.0.

> ---
> v1: https://lists.gnu.org/archive/html/qemu-devel/2018-07/msg05089.html
> Changes from v1:
>    Fixed the commit message as suggested
> 
>  linux-user/host/ppc64/safe-syscall.inc.S |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/linux-user/host/ppc64/safe-syscall.inc.S b/linux-user/host/ppc64/safe-syscall.inc.S
> index d30050a67c..b0cbbe6a69 100644
> --- a/linux-user/host/ppc64/safe-syscall.inc.S
> +++ b/linux-user/host/ppc64/safe-syscall.inc.S
> @@ -49,7 +49,7 @@ safe_syscall_base:
>  	 *               and returns the result in r3
>  	 * Shuffle everything around appropriately.
>  	 */
> -	mr	11, 3	/* signal_pending */
> +	mr	14, 3	/* signal_pending */
>  	mr	0, 4	/* syscall number */
>  	mr	3, 5	/* syscall arguments */
>  	mr	4, 6
> @@ -67,7 +67,7 @@ safe_syscall_base:
>  	 */
>  safe_syscall_start:
>  	/* if signal_pending is non-zero, don't do the call */
> -	lwz	12, 0(11)
> +	lwz	12, 0(14)
>  	cmpwi	0, 12, 0
>  	bne-	0f
>  	sc
> 
> 

-- 
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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