On Wed, 9 Jul 2025 12:01:14 +0200
Jens Remus <jremus@xxxxxxxxxxxxx> wrote:
> > static int unwind_user_next(struct unwind_user_state *state)
> > {
> > - /* no implementation yet */
> > + struct unwind_user_frame *frame;
> > + unsigned long cfa = 0, fp, ra = 0;
> > + unsigned int shift;
> > +
> > + if (state->done)
> > + return -EINVAL;
> > +
> > + if (fp_state(state))
> > + frame = &fp_frame;
> > + else
> > + goto done;
> > +
> > + if (frame->use_fp) {
> > + if (state->fp < state->sp)
>
> if (state->fp <= state->sp)
>
> I meanwhile came to the conclusion that for architectures, such as s390,
> where SP at function entry == SP at call site, the FP may be equal to
> the SP. At least for the brief period where the FP has been setup and
> stack allocation did not yet take place. For most architectures this
> can probably only occur in the topmost frame. For s390 the FP is setup
> after static stack allocation, so --fno-omit-frame-pointer would enforce
> FP==SP in any frame that does not perform dynamic stack allocation.
