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 <sb...@linux.vnet.ibm.com> --- v2: https://lists.gnu.org/archive/html/qemu-devel/2018-07/msg05102.html Changes from v2: Added code to store and restore r14 register. 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 | 7 +++++-- 1 file changed, 5 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..ca85da13bd 100644 --- a/linux-user/host/ppc64/safe-syscall.inc.S +++ b/linux-user/host/ppc64/safe-syscall.inc.S @@ -49,7 +49,8 @@ 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 */ + mr 14, 3 /* signal_pending */ mr 0, 4 /* syscall number */ mr 3, 5 /* syscall arguments */ mr 4, 6 @@ -67,11 +68,12 @@ 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: + ld 14, 16(1) /* restore r14 to its original value */ /* code path when we did execute the syscall */ bnslr+ @@ -81,6 +83,7 @@ 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
