From: David Gibson <david@gibson.dropbear.id.au>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: Shivaprasad G Bhat <sbhat@linux.vnet.ibm.com>,
dgibson@redhat.com, riku.voipio@iki.fi, laurent@vivier.eu,
qemu-ppc@nongnu.org, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] linux-user: ppc64: don't use volatile register during safe_syscall
Date: Fri, 27 Jul 2018 15:34:09 +1000 [thread overview]
Message-ID: <20180727053409.GL3694@umbus.fritz.box> (raw)
In-Reply-To: <c162e499-1429-7863-4a1a-58cfbb4d3057@linaro.org>
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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 <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.
>
> 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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prev parent reply other threads:[~2018-07-27 5:39 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-26 8:26 [Qemu-devel] [PATCH v2] linux-user: ppc64: don't use volatile register during safe_syscall Shivaprasad G Bhat
2018-07-27 3:13 ` [Qemu-devel] [Qemu-ppc] " David Gibson
2018-07-27 5:20 ` Richard Henderson
2018-07-27 5:34 ` David Gibson [this message]
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