http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57260
rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2013-05-14
CC| |rsandifo at gcc dot gnu.org
Assignee|unassigned at gcc dot gnu.org |rsandifo at gcc dot
gnu.org
Ever confirmed|0 |1
--- Comment #10 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org>
---
Confirmed.
As discusseded on the binutils list, this is definitely a bug IMO.
It's a QoI requirement that we use lazy binding for direct calls.
I don't think I'd realised quite how important that is when
I implemented sibling calls for PIC way back when.
As for why GCC is using %got_disp for sibling calls: the problem
is that lazy-binding stubs require $gp to be valid on entry.
And $gp is call-saved on n32 and n64, so functions must restore
the _caller's_ value of $gp before returning from a function.
This means that $gp might hold the wrong value on entry to a
sibcalled stub.
I think the fix is simply to disable direct sibling calls for
n32 and n64 non-PLT abicalls. (o32 is OK, because $gp is call-clobbered
there.) It's unfortunate that we lose optimisation for a once-per-run
thing, but I don't think there's any alternative.
