On Mon, 2026-02-09 at 20:51 -0800, H. Peter Anvin wrote:
> On 2026-02-09 19:11, Xi Ruoyao 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?
> >
>
> Well, it looks like this might be a non-manifest bug on x86 *IN THIS CASE*,
But only if after the patch _Unwind_Find_FDE returns NULL here (instead
of a FDE of another function). I've not verified it on x86. If glibc
tests (specifically misc/tst-sigcontext-get_pc) work fine things should
be fine.
/* snip */
> Could you file a gcc bug on this?
Will do.
--
Xi Ruoyao <[email protected]>
