On 07/25/2018 11:48 PM, 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. > > Signed-off-by: Shivaprasad G Bhat <sb...@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 > > 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 */
I do see that I was incorrect in assuming that r11 would be unmodified. But you can't simply write to a call-saved register -- you must preserve its value for the caller. Saving the value requires that you find some space on, or create, a stack frame. Note that there are two different conventions for _CALL_AIX and _CALL_ELF==2. r~
