qemu/linux-user/host/ppc64
Shivaprasad G Bhat 5d9f3ea081 linux-user: ppc64: don't use volatile register during safe_syscall
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.
Use SP+16 which is a slot for LR, for save/restore of previous value
of r14. SP+16 can be used, as LR is preserved across the 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
https://openpowerfoundation.org/wp-content/uploads/2016/03/ABI64BitOpenPOWERv1.1_16July2015_pub4.pdf

Signed-off-by: Shivaprasad G Bhat <sbhat@linux.vnet.ibm.com>
Tested-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <153301568965.30312.10498134581068746871.stgit@dhcp-9-109-246-16>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
2018-07-31 09:57:43 +02:00
..
hostdep.h Replace 'struct ucontext' with 'ucontext_t' type 2017-07-20 10:10:28 +01:00
safe-syscall.inc.S linux-user: ppc64: don't use volatile register during safe_syscall 2018-07-31 09:57:43 +02:00