From: "Ulrich Weigand" <uweigand@de.ibm.com>
To: dan@codesourcery.com (Daniel Jacobowitz)
Cc: gdb-patches@sourceware.org, rearnsha@arm.com,
matthew.gretton-dann@arm.com
Subject: Re: [rfc/rfa] Use ARM exception tables as GDB unwinder
Date: Thu, 21 Oct 2010 20:29:00 -0000 [thread overview]
Message-ID: <201010212029.o9LKTWpN013394@d12av02.megacenter.de.ibm.com> (raw)
In-Reply-To: <20101021184229.GR8337@caradoc.them.org> from "Daniel Jacobowitz" at Oct 21, 2010 02:42:30 PM
Dan Jacobowitz wrote:
> On Thu, Oct 21, 2010 at 08:26:09PM +0200, Ulrich Weigand wrote:
> > One issue with this just occurred to me: comparing personality routines
> > by *name* relies on symbol information being present. Since we're doing
> > the whole ARM unwinder support primarily to better cope with the case
> > where symbol information is absent, this may be counter-productive ...
> >
> > Is there some other way to recognize those particular unwinders?
>
> Yes, it's true that this requires names. Fortunately, in the usual
> case they are in the dynamic symbol table. So, I think you'll have
> the names - or do we not see dynamic symbols here?
Hmm, I was confused by readelf apparently being unable to resolve
them in the case of libstdc++:
Unwind table index '.ARM.exidx' at offset 0x95768 contains 1433 entries:
0x44704: 0x1 [cantunwind]
0x4478c: 0x80aab0b0
Compact model 0
0xaa pop {r4, r5, r6r14}
0xb0 finish
0xb0 finish
0x44804: 0x1 [cantunwind]
0x44938: @0x8fec0
Personality routine: 0x43264
0x44990: @0x8fedc
Personality routine: 0x43264
0x44b00: 0x1 [cantunwind]
But in fact 0x43264 is the address of the PLT entry pointing to this
jump slot:
000a4480 000d7516 R_ARM_JUMP_SLOT 00084e25 __gxx_personality_v0
So we should certainly be able to resolve that in GDB.
> > Another, related topic: Running the GDB testsuite on a system without
> > debug/symbol info, I'm still seeing failures in unwinding from interrupted
> > system calls. This is because the assembler code to do the syscall
> > clobbers r7 without generating appropriate unwind records, and thus
> > unwinding fails somewhere higher up the stack.
> >
> > Now, this is exactly the problem you fixed by moving the actual syscall
> > into a separate routine __libc_do_syscall. However, this routine is
> > only called from C code built for -mthumb. C code built for -marm,
> > as well as code originally in (ARM) assembler, will continue to use
> > inline sequences clobbering r7.
>
> This should work... the problem with r7 was that it's the hard frame
> pointer for Thumb (even Thumb-2 - although it shouldn't be, most
> likely, it's a wasteful choice). So we couldn't mark it as
> clobbered. Does GCC not mark r7 as saved on the stack for the ARM
> code? It should know perfectly well that r7 is not unchanged.
Right, for C code there should be no problem. The problems I've been
seeing all come from *assembler* source files using the DO_CALL macro.
This gets CFI correct, but doesn't create any unwind records ...
Bye,
Ulrich
--
Dr. Ulrich Weigand
GNU Toolchain for Linux on System z and Cell BE
Ulrich.Weigand@de.ibm.com
next prev parent reply other threads:[~2010-10-21 20:29 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-20 0:01 Ulrich Weigand
2010-10-20 11:14 ` Matthew Gretton-Dann
2010-10-21 15:39 ` Ulrich Weigand
2010-10-20 13:27 ` Daniel Jacobowitz
2010-10-21 15:51 ` Ulrich Weigand
2010-10-21 16:02 ` Daniel Jacobowitz
2010-10-21 18:26 ` Ulrich Weigand
2010-10-21 18:42 ` Daniel Jacobowitz
2010-10-21 20:29 ` Ulrich Weigand [this message]
2010-10-21 20:43 ` Daniel Jacobowitz
2010-12-01 16:45 ` Ulrich Weigand
2010-12-12 4:21 ` Daniel Jacobowitz
2010-12-12 12:24 ` Andreas Schwab
2011-03-09 19:11 ` Ulrich Weigand
2011-03-11 22:35 ` Daniel Jacobowitz
2011-03-19 4:25 ` Ulrich Weigand
2011-03-21 14:51 ` Daniel Jacobowitz
2011-03-21 20:06 ` Ulrich Weigand
2010-10-21 22:26 ` Ulrich Weigand
2010-10-26 13:43 ` Daniel Jacobowitz
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=201010212029.o9LKTWpN013394@d12av02.megacenter.de.ibm.com \
--to=uweigand@de.ibm.com \
--cc=dan@codesourcery.com \
--cc=gdb-patches@sourceware.org \
--cc=matthew.gretton-dann@arm.com \
--cc=rearnsha@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).