Commit ed1ca2777c35fe2f2751de255df3e16f17bdbd8d
2014-11-24T13:02:03
x86: Remove use of .cfi_escape The unwind info isn't 100% correct at all points during the epilogue, and not annotating is just as incorrect as the annotation. This works better on systems that do not support DW_OP_call_frame_cfa.
diff --git a/src/x86/sysv.S b/src/x86/sysv.S
index bb9d568..f737371 100644
--- a/src/x86/sysv.S
+++ b/src/x86/sysv.S
@@ -405,16 +405,11 @@ C(ffi_closure_STDCALL):
movl closure_FS(%esp), %edx /* move return address */
movl %edx, (%ecx)
- /* New pseudo-stack frame based off ecx. This is unwind trickery
- in that the CFA *has* changed, to the proper popped stack address.
- Note that the location to which we moved the return address
- is the new CFA-4, so that's unchanged. */
- cfi_def_cfa(%ecx, 4)
- /* Normally esp is unwound to CFA + the caller's ARGS_SIZE.
- We've just set the CFA to that final value. Tell the unwinder
- to restore esp from CFA without the ARGS_SIZE:
- DW_CFA_val_expression %esp, DW_OP_call_frame_cfa. */
- cfi_escape(0x16, 4, 1, 0x9c)
+ /* From this point on, the value of %esp upon return is %ecx+4,
+ and we've copied the return address to %ecx to make return easy.
+ There's no point in representing this in the unwind info, as
+ there is always a window between the mov and the ret which
+ will be wrong from one point of view or another. */
FFI_CLOSURE_MASK_AND_JUMP