From: Josh Kunz via Qemu-devel <qemu-devel@nongnu.org>
To: Laurent Vivier <laurent@vivier.eu>
Cc: qemu-trivial@nongnu.org, Riku Voipio <riku.voipio@iki.fi>,
qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] linux-user: Support gdb 'qOffsets' query for ELF
Date: Tue, 3 Sep 2019 12:19:45 -0700 [thread overview]
Message-ID: <CADgy-2tzD0FVXbKtadSL1JuMWW_TEzFP2ZD0hzA4PUnxh1Xz0g@mail.gmail.com> (raw)
In-Reply-To: <5b4df64c-40e4-70cd-753e-f52e2b547c18@vivier.eu>
The `Data` and `Code` flags in `qOffsets` are actually section offsets
rather than segment offsets. GDB relocates the symbols in those sections
relative to their location in the binary. So we have to use `load_bias`.
See here for a more detailed description:
https://sourceware.org/gdb/onlinedocs/gdb/General-Query-Packets.html#General-Query-Packets
On Mon, Aug 26, 2019 at 1:29 AM Laurent Vivier <laurent@vivier.eu> wrote:
> Le 17/08/2019 à 01:34, Josh Kunz via Qemu-devel a écrit :
> > This is needed to support debugging PIE ELF binaries running under QEMU
> > user mode. Currently, `code_offset` and `data_offset` remain unset for
> > all ELF binaries, so GDB is unable to correctly locate the position of
> > the binary's text and data.
> >
> > The fields `code_offset`, and `data_offset` were originally added way
> > back in 2006 to support debugging of bFMT executables (978efd6aac6),
> > and support was just never added for ELF. Since non-PIE binaries are
> > loaded at exactly the address specified in the binary, GDB does not need
> > to relocate any symbols, so the buggy behavior is not normally observed.
> >
> > Buglink: https://bugs.launchpad.net/qemu/+bug/1528239
> > Signed-off-by: Josh Kunz <jkz@google.com>
> > ---
> > linux-user/elfload.c | 2 ++
> > 1 file changed, 2 insertions(+)
>
> As it seems they are text and data segment offsets, why it's not based
> on info->start_code and info->start_data?
>
> Thanks,
> Laurent
>
next prev parent reply other threads:[~2019-09-03 19:20 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-16 23:34 [Qemu-devel] [PATCH] linux-user: Support gdb 'qOffsets' query for ELF Josh Kunz via Qemu-devel
2019-08-16 23:36 ` Josh Kunz via Qemu-devel
2019-08-17 1:35 ` no-reply
2019-08-26 8:29 ` Laurent Vivier
2019-09-03 19:19 ` Josh Kunz via Qemu-devel [this message]
2019-09-04 5:23 ` Laurent Vivier
2019-09-05 10:54 ` Philippe Mathieu-Daudé
2019-09-10 8:23 ` Laurent Vivier
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=CADgy-2tzD0FVXbKtadSL1JuMWW_TEzFP2ZD0hzA4PUnxh1Xz0g@mail.gmail.com \
--to=qemu-devel@nongnu.org \
--cc=jkz@google.com \
--cc=laurent@vivier.eu \
--cc=qemu-trivial@nongnu.org \
--cc=riku.voipio@iki.fi \
/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 NNTP newsgroup(s).