Use cfi directives in the x86-64 safe_syscall to allow gdb to get
backtraces right from within it. (In particular this will be
quite a common situation if the user interrupts QEMU while it's
in a blocked safe-syscall: at the point of the syscall insn RBP
is in use for something else, and so gdb can't find the frame then
without assistance.)
Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
---
The requirements for frame information annotations seem to be a bit
of an undocumented black art, but I think I have these right. At
any rate, gdb now gives correct backtraces from all points in
the routine as far as I can see. Review appreciated...
linux-user/host/x86_64/safe-syscall.inc.S | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/linux-user/host/x86_64/safe-syscall.inc.S
b/linux-user/host/x86_64/safe-syscall.inc.S
index dde434c..bbb1eca 100644
--- a/linux-user/host/x86_64/safe-syscall.inc.S
+++ b/linux-user/host/x86_64/safe-syscall.inc.S
@@ -24,6 +24,7 @@
* -1-and-errno-set convention is done by the calling wrapper.
*/
safe_syscall_base:
+ .cfi_startproc
/* This saves a frame pointer and aligns the stack for the syscall.
* (It's unclear if the syscall ABI has the same stack alignment
* requirements as the userspace function call ABI, but better safe
than
@@ -31,6 +32,8 @@ safe_syscall_base:
* does not list any ABI differences regarding stack alignment.)
*/
push %rbp
+ .cfi_def_cfa_offset 16
+ .cfi_offset rbp,-16
/* The syscall calling convention isn't the same as the
* C one:
@@ -70,12 +73,19 @@ safe_syscall_start:
safe_syscall_end:
/* code path for having successfully executed the syscall */
pop %rbp
+ .cfi_remember_state
+ .cfi_def_cfa_offset 8
+ .cfi_restore ebp
ret
return_ERESTARTSYS:
/* code path when we didn't execute the syscall */
+ .cfi_restore_state
mov $-TARGET_ERESTARTSYS, %rax
pop %rbp
+ .cfi_def_cfa_offset 8
+ .cfi_restore ebp
ret
+ .cfi_endproc
.size safe_syscall_base, .-safe_syscall_base
--
1.9.1
