[hppa] FYI: confusion in unwind descriptor field meaning

[Jim Blandy]

On 11/11/05, Randolph Chung <randolph@tausq.org> wrote:
> >>For that matter, how do you find the beginning of the function without
> >>unwind data?
> >
> > Linker symbols.  If you don't have them, then prologue analysis isn't useful.
>
> This is what I meant - on hppa, even without linker symbols, we can
> still do prologue analysis because the ABI mandates unwind records. So
> we can actually do unwinding more robustly based on the unwind records.
> This is especially useful when you have mixed code compiled with
> different flags and/or have been stripped.

Hmm.  Is it possible to find a function's entry point from a PC within
that function's code given only the unwind records?  If the detailed
contents of the unwind records are difficult to interpret accurately,
but we can accurately recover entry points from them, and prologue
analysis works, then we could use the unwind records *only* to
discover entry points, and then use prologue analysis to actually get
the unwind information.

I'm sounding like some kind of prologue analysis fanatic here, but
really I'm not.   We should make the best use of the techniques and
information available, and it sounds to me like prologue analysis is
comparable with the alternatives here, if we can find the information
it needs.