From: "Philippe Mathieu-Daudé" <philmd@redhat.com>
To: "Josh Kunz" <jkz@google.com>,
"Laurent Vivier" <laurent@vivier.eu>,
"Alex Bennée" <alex.bennee@linaro.org>
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: Thu, 5 Sep 2019 12:54:13 +0200 [thread overview]
Message-ID: <fe428dbd-a9f4-42c0-bb12-8c14fb3e2489@redhat.com> (raw)
In-Reply-To: <CADgy-2tzD0FVXbKtadSL1JuMWW_TEzFP2ZD0hzA4PUnxh1Xz0g@mail.gmail.com>
Cc'ing Alex.
On 9/3/19 9:19 PM, Josh Kunz via Qemu-devel wrote:
> 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
Maybe we can amend a reference to
http://sourceware.org/gdb/onlinedocs/gdb/General-Query-Packets.html#index-qOffsets-packet
in the commit.
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> 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:[~2019-09-05 10:55 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
2019-09-04 5:23 ` Laurent Vivier
2019-09-05 10:54 ` Philippe Mathieu-Daudé [this message]
2019-09-10 8:23 ` Laurent Vivier
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