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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>
This commit is contained in:
Shivaprasad G Bhat 2018-07-31 11:12:24 +05:30 committed by Laurent Vivier
parent 28cbb997d6
commit 5d9f3ea081
1 changed files with 6 additions and 2 deletions
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8
linux-user/host/ppc64/safe-syscall.inc.S
View File

@ -49,7 +49,9 @@ safe_syscall_base:
* and returns the result in r3
* Shuffle everything around appropriately.
*/
mr 11, 3 /* signal_pending */
std 14, 16(1) /* Preserve r14 in SP+16 */
.cfi_offset 14, 16
mr 14, 3 /* signal_pending */
mr 0, 4 /* syscall number */
mr 3, 5 /* syscall arguments */
mr 4, 6
@ -67,12 +69,13 @@ 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
safe_syscall_end:
/* code path when we did execute the syscall */
ld 14, 16(1) /* restore r14 to its original value */
bnslr+
/* syscall failed; return negative errno */
@ -81,6 +84,7 @@ safe_syscall_end:
/* code path when we didn't execute the syscall */
0: addi 3, 0, -TARGET_ERESTARTSYS
ld 14, 16(1) /* restore r14 to its orginal value */
blr
.cfi_endproc