Richard Sandiford wrote: > In other words, the reason seemed to be that the _Unwind_SetGRPtr in: > > #ifdef EH_RETURN_STACKADJ_RTX > /* Special handling here: Many machines do not use a frame pointer, > and track the CFA only through offsets from the stack pointer from > one frame to the next. In this case, the stack pointer is never > stored, so it has no saved address in the context. What we do > have is the CFA from the previous stack frame. > > In very special situations (such as unwind info for signal return), > there may be location expressions that use the stack pointer as well. > > Do this conditionally for one frame. This allows the unwind info > for one frame to save a copy of the stack pointer from the previous > frame, and be able to use much easier CFA mechanisms to do it. > Always zap the saved stack pointer value for the next frame; carrying > the value over from one frame to another doesn't make sense. */ > > _Unwind_SpTmp tmp_sp; > > if (!_Unwind_GetGRPtr (&orig_context, __builtin_dwarf_sp_column ())) > _Unwind_SetSpColumn (&orig_context, context->cfa, &tmp_sp); > _Unwind_SetGRPtr (context, __builtin_dwarf_sp_column (), NULL); > #endif > > was conditional on EH_RETURN_STACKADJ_RTX being defined. It looked at > first glance like things would work if that call was moved outside, > so that we never inherit save slots for the stack pointer. Does that > make sense? I can give it a go tomorrow if so.
I haven't looked into this in detail right now, but I recall that I had to specifically add that #ifdef a long time ago since unwinding wouldn't work correctly on s390 otherwise: http://gcc.gnu.org/ml/gcc-patches/2003-05/msg00904.html And the background of the bug here: http://gcc.gnu.org/ml/gcc/2003-05/msg00536.html Actually, now I think the problem originally described there is still valid: on s390 the CFA is *not* equal to the value at function entry, but biased by 96/160 bytes. So setting the SP to the CFA is wrong ... Bye, Ulrich -- Dr. Ulrich Weigand GNU/Linux compilers and toolchain ulrich.weig...@de.ibm.com
