Re: PATCH: PIC_OFFSET_TABLE_REGNUM_SAVED should be call used when

[Alan Modra <alan at linuxcare dot com dot au>]

On Sun, 14 Jan 2001, John David Anglin wrote:

> > > > Oops, there is a problem.  The PIC_OFFSET_TABLE_REGNUM_SAVED register
> > > > must be call used under all conditions since non PIC code has to be able
> > > > to call PIC code.
> > > 
> > > On further thought, the PIC_OFFSET_TABLE_REGNUM_SAVED can't be a call used
> > > register since this will break the run-time ABI.  I think this means that
> > > it can't be a fixed register as well.  Need a different solution.
> > 
> > Why will that break the ABI?  New code will just assume that r4 isn't
> > preserved over calls, but it's no problem if in fact r4 is preserved.  It
> 
> If we make r4 call used, it isn't saved by the callee.

Hit's self on head.  Indeed.  Here's another curious little problem.

---
extern void bar (void);

#define trash_r27 \
  do                                            \
    {                                           \
      register int x asm ("r27");               \
      asm volatile ("ldi 0,%0" : "=&r" (x) : "0" (x) ); \
    }                                           \
  while (0)

int main (void)
{
  trash_r27 (bar);
  bar ();
  return 0;
}
---

With yesterday's sourceware CVS, hppa64-hpux11-gcc doesn't seem to see any
need to reload r27 for the call to bar.  This problem came to light when I
was investigating how to fix the calls which get pasted into _init (which
also don't reload r27, or r19 in 32 bit case, and so lose if there is more
than one pasted call).

Alan Modra
--
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