From: Michal Ludvig <mludvig@suse.cz>
To: Mark Kettenis <kettenis@chello.nl>
Cc: gdb <gdb@sources.redhat.com>
Subject: dwarf-frame.c question
Date: Tue, 27 May 2003 15:19:00 -0000 [thread overview]
Message-ID: <3ED381CB.5050207@suse.cz> (raw)
Hi Mark,
why do you decrement unwound PC in dwarf_frame_cache() before using it?
dwarf-frame.c:
478 /* Unwind the PC. */
479 fs->pc = frame_pc_unwind (next_frame);
480 if (get_frame_type (next_frame) == NORMAL_FRAME
481 && frame_relative_level (next_frame) >= 0)
482 fs->pc--;
This makes a problem for a signal trampoline.
If it is sitting on addresses say 0x40000140-0x40000150, the return
address from signal handler is 0x40000140, but dwarf_frame_cache() says
it is 0x4000013f and couldn't find it's CFI...
This has a tragic consequence few lines below were you look for FDE but
don't check if you find one. If you don't, line 488 segfaults.
484 /* Find the correct FDE. */
485 fde = dwarf_frame_find_fde (&fs->pc);
486
487 /* Extract any interesting information from the CIE. */
488 fs->data_align = fde->cie->data_alignment_factor;
489 fs->code_align = fde->cie->code_alignment_factor;
490 fs->retaddr_column = fde->cie->return_address_register;
The problem is, that dwarf_frame_p() looks for the real return address
and says that there is a debug info and sets unwinder to use dwarf2
methods for this farme.
But the in unwinder itself in dwarf_frame_cache() looks for the
decreased one and of course doesn't find it.
I couldn't see any problems when I removed the decrementation, so why is
it there?
Michal Ludvig
--
* SuSE CR, s.r.o * mludvig@suse.cz
* (+420) 296.545.373 * http://www.suse.cz
next reply other threads:[~2003-05-27 15:19 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-05-27 15:19 Michal Ludvig [this message]
2003-05-29 15:44 ` Mark Kettenis
2003-05-29 19:54 ` Andrew Cagney
2003-05-29 22:22 ` Mark Kettenis
2003-05-29 22:43 ` Michal Ludvig
2003-05-29 23:13 ` Andrew Cagney
2003-05-30 1:34 ` Daniel Jacobowitz
2003-05-30 20:21 ` Jim Blandy
2003-05-30 20:21 ` Jim Blandy
2003-05-30 20:32 ` Andrew Cagney
2003-06-03 0:04 ` Jim Blandy
2003-06-03 5:47 ` Richard Henderson
2003-06-03 6:32 ` Jim Blandy
2003-06-03 15:58 ` Richard Henderson
2003-06-03 17:38 ` Richard Henderson
2003-06-03 20:12 ` Alexandre Oliva
2003-05-30 20:44 ` Alexandre Oliva
2003-06-01 5:59 Richard Henderson
2003-06-01 10:00 ` Mark Kettenis
2003-06-02 20:34 ` Richard Henderson
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