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linux-user: provide frame information in x86-64 safe_syscall 

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.maydell@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
This commit is contained in:
Peter Maydell 2016-06-06 19:56:54 +01:00 committed by Riku Voipio
parent 90c0f080fe
commit 9e024732f5
1 changed files with 10 additions and 0 deletions
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10
linux-user/host/x86_64/safe-syscall.inc.S
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@ -24,6 +24,7 @@
* -1-and-errno-set convention is done by the calling wrapper. * -1-and-errno-set convention is done by the calling wrapper.
*/ */
safe_syscall_base: safe_syscall_base:
.cfi_startproc
/* This saves a frame pointer and aligns the stack for the syscall. /* This saves a frame pointer and aligns the stack for the syscall.
* (It's unclear if the syscall ABI has the same stack alignment * (It's unclear if the syscall ABI has the same stack alignment
* requirements as the userspace function call ABI, but better safe than * 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.) * does not list any ABI differences regarding stack alignment.)
*/ */
push %rbp push %rbp
.cfi_adjust_cfa_offset 8
.cfi_rel_offset rbp, 0
/* The syscall calling convention isn't the same as the /* The syscall calling convention isn't the same as the
* C one: * C one:
@ -70,12 +73,19 @@ safe_syscall_start:
safe_syscall_end: safe_syscall_end:
/* code path for having successfully executed the syscall */ /* code path for having successfully executed the syscall */
pop %rbp pop %rbp
.cfi_remember_state
.cfi_def_cfa_offset 8
.cfi_restore rbp
ret ret
return_ERESTARTSYS: return_ERESTARTSYS:
/* code path when we didn't execute the syscall */ /* code path when we didn't execute the syscall */
.cfi_restore_state
mov $-TARGET_ERESTARTSYS, %rax mov $-TARGET_ERESTARTSYS, %rax
pop %rbp pop %rbp
.cfi_def_cfa_offset 8
.cfi_restore rbp
ret ret
.cfi_endproc
.size safe_syscall_base, .-safe_syscall_base .size safe_syscall_base, .-safe_syscall_base