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Re: [RFA patch] PR18749: epilogue not tracked in dwarf2 unwind-info
- From: Alan Modra <amodra at bigpond dot net dot au>
- To: Michael Matz <matz at suse dot de>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Wed, 14 Jun 2006 11:49:51 +0930
- Subject: Re: [RFA patch] PR18749: epilogue not tracked in dwarf2 unwind-info
- References: <Pine.LNX.4.58.0606122139440.4311@wotan.suse.de>
On Mon, Jun 12, 2006 at 10:07:40PM +0200, Michael Matz wrote:
> I'm trying to fix PR18749, which is about the fact that dwarf2out.c
> doesn't look at epilogues at all, which makes the CFA be wrong during the
> epilogue, as no adjustments there (like pops, or additions to the stack
> pointer) are tracked.
You need to have some compelling reason to emit the unwind info, because
doing so will bloat .eh_frame dramatically (*). gcc doesn't support
asynchronous exceptions, shouldn't generate trapping instructions in
epilogues, and shouldn't allow trapping instructions from the body to
migrate into the epilogue.
*) You may have multiple copies of the epilogue. You may have code from
the function body being placed after the function return. It's not just
a matter of tracking the cfa adjustment in the epilogue; A proper eh
description for unwinding through asynchronous exceptions needs to know
that saved regs are no longer valid on the stack.
--
Alan Modra
IBM OzLabs - Linux Technology Centre