Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] linux-user: ppc64: don't use volatile register during safe_syscall
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 > Tested-by: Laurent Vivier > Reviewed-by: Laurent Vivier 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 signature.asc Description: PGP signature
Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] linux-user: ppc64: don't use volatile register during safe_syscall
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 >> Tested-by: Laurent Vivier >> Reviewed-by: Laurent Vivier > > Applied to ppc-for-3.0. No please! r14 is a call-saved register and needs saving before clobbering. r~
Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] linux-user: ppc64: don't use volatile register during safe_syscall
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 > >> Tested-by: Laurent Vivier > >> Reviewed-by: Laurent Vivier > > > > 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 signature.asc Description: PGP signature
