Re: [PATCH v4.1 06/10] x86/entry/vdso32: remove open-coded DWARF in sigreturn.S

[H. Peter Anvin]

On February 9, 2026 7:11:25 PM PST, Xi Ruoyao <xry111@xxxxxxxxxxx> wrote:
>On Mon, 2026-02-02 at 19:57 -0800, H. Peter Anvin wrote:
>> That hack dates back from before the signal frame extension. It is no
>> longer necessary.
>
>Unfortunately at least it seems libgcc unwinder does not handle the
>signal frame extension properly.  The code reads:
>
>  fde = _Unwind_Find_FDE (context->ra + _Unwind_IsSignalFrame (context) - 1, 
>                          &context->bases);
>  if (fde == NULL)
>    {    
>#ifdef MD_FALLBACK_FRAME_STATE_FOR
>      /* Couldn't find frame unwind info for this function.  Try a
>         target-specific fallback mechanism.  This will necessarily
>         not provide a personality routine or LSDA.  */
>      return MD_FALLBACK_FRAME_STATE_FOR (context, fs); 
>#else
>      return _URC_END_OF_STACK;
>#endif
>    }    
>
>  fs->pc = context->bases.func;
>
>  cie = get_cie (fde);
>  insn = extract_cie_info (cie, context, fs); 
>
>Thus, it indeed attempts to avoid subtracting 1 for a signal frame, but
>... _Unwind_IsSignalFrame (context) actually extracts a flag in context
>which will only be raised up by extract_cie_info.
>
>Or am I missing something here?
>

Oh, good grief...

How does this possibly work on non-x86 platforms?