linux-user: Support gdb 'qOffsets' query for ELF
diff mbox series

Message ID 20190816233422.16715-1-jkz@google.com
State New
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Series
  • linux-user: Support gdb 'qOffsets' query for ELF
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Commit Message

Sam Eiderman via Qemu-devel Aug. 16, 2019, 11:34 p.m. UTC
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(+)

Comments

no-reply@patchew.org Aug. 17, 2019, 1:35 a.m. UTC | #1
Patchew URL: https://patchew.org/QEMU/20190816233422.16715-1-jkz@google.com/



Hi,

This series seems to have some coding style problems. See output below for
more information:

Type: series
Subject: [Qemu-devel] [PATCH] linux-user: Support gdb 'qOffsets' query for ELF
Message-id: 20190816233422.16715-1-jkz@google.com

=== TEST SCRIPT BEGIN ===
#!/bin/bash
git rev-parse base > /dev/null || exit 0
git config --local diff.renamelimit 0
git config --local diff.renames True
git config --local diff.algorithm histogram
./scripts/checkpatch.pl --mailback base..
=== TEST SCRIPT END ===

Updating 3c8cf5a9c21ff8782164d1def7f44bd888713384
From https://github.com/patchew-project/qemu
 * [new tag]         patchew/20190816233422.16715-1-jkz@google.com -> patchew/20190816233422.16715-1-jkz@google.com
Submodule 'capstone' (https://git.qemu.org/git/capstone.git) registered for path 'capstone'
Submodule 'dtc' (https://git.qemu.org/git/dtc.git) registered for path 'dtc'
Submodule 'roms/QemuMacDrivers' (https://git.qemu.org/git/QemuMacDrivers.git) registered for path 'roms/QemuMacDrivers'
Submodule 'roms/SLOF' (https://git.qemu.org/git/SLOF.git) registered for path 'roms/SLOF'
Submodule 'roms/edk2' (https://git.qemu.org/git/edk2.git) registered for path 'roms/edk2'
Submodule 'roms/ipxe' (https://git.qemu.org/git/ipxe.git) registered for path 'roms/ipxe'
Submodule 'roms/openbios' (https://git.qemu.org/git/openbios.git) registered for path 'roms/openbios'
Submodule 'roms/openhackware' (https://git.qemu.org/git/openhackware.git) registered for path 'roms/openhackware'
Submodule 'roms/opensbi' (https://git.qemu.org/git/opensbi.git) registered for path 'roms/opensbi'
Submodule 'roms/qemu-palcode' (https://git.qemu.org/git/qemu-palcode.git) registered for path 'roms/qemu-palcode'
Submodule 'roms/seabios' (https://git.qemu.org/git/seabios.git/) registered for path 'roms/seabios'
Submodule 'roms/seabios-hppa' (https://git.qemu.org/git/seabios-hppa.git) registered for path 'roms/seabios-hppa'
Submodule 'roms/sgabios' (https://git.qemu.org/git/sgabios.git) registered for path 'roms/sgabios'
Submodule 'roms/skiboot' (https://git.qemu.org/git/skiboot.git) registered for path 'roms/skiboot'
Submodule 'roms/u-boot' (https://git.qemu.org/git/u-boot.git) registered for path 'roms/u-boot'
Submodule 'roms/u-boot-sam460ex' (https://git.qemu.org/git/u-boot-sam460ex.git) registered for path 'roms/u-boot-sam460ex'
Submodule 'slirp' (https://git.qemu.org/git/libslirp.git) registered for path 'slirp'
Submodule 'tests/fp/berkeley-softfloat-3' (https://git.qemu.org/git/berkeley-softfloat-3.git) registered for path 'tests/fp/berkeley-softfloat-3'
Submodule 'tests/fp/berkeley-testfloat-3' (https://git.qemu.org/git/berkeley-testfloat-3.git) registered for path 'tests/fp/berkeley-testfloat-3'
Submodule 'ui/keycodemapdb' (https://git.qemu.org/git/keycodemapdb.git) registered for path 'ui/keycodemapdb'
Cloning into 'capstone'...
Submodule path 'capstone': checked out '22ead3e0bfdb87516656453336160e0a37b066bf'
Cloning into 'dtc'...
Submodule path 'dtc': checked out '88f18909db731a627456f26d779445f84e449536'
Cloning into 'roms/QemuMacDrivers'...
Submodule path 'roms/QemuMacDrivers': checked out '90c488d5f4a407342247b9ea869df1c2d9c8e266'
Cloning into 'roms/SLOF'...
Submodule path 'roms/SLOF': checked out 'ba1ab360eebe6338bb8d7d83a9220ccf7e213af3'
Cloning into 'roms/edk2'...
Submodule path 'roms/edk2': checked out '20d2e5a125e34fc8501026613a71549b2a1a3e54'
Submodule 'SoftFloat' (https://github.com/ucb-bar/berkeley-softfloat-3.git) registered for path 'ArmPkg/Library/ArmSoftFloatLib/berkeley-softfloat-3'
Submodule 'CryptoPkg/Library/OpensslLib/openssl' (https://github.com/openssl/openssl) registered for path 'CryptoPkg/Library/OpensslLib/openssl'
Cloning into 'ArmPkg/Library/ArmSoftFloatLib/berkeley-softfloat-3'...
Submodule path 'roms/edk2/ArmPkg/Library/ArmSoftFloatLib/berkeley-softfloat-3': checked out 'b64af41c3276f97f0e181920400ee056b9c88037'
Cloning into 'CryptoPkg/Library/OpensslLib/openssl'...
Submodule path 'roms/edk2/CryptoPkg/Library/OpensslLib/openssl': checked out '50eaac9f3337667259de725451f201e784599687'
Submodule 'boringssl' (https://boringssl.googlesource.com/boringssl) registered for path 'boringssl'
Submodule 'krb5' (https://github.com/krb5/krb5) registered for path 'krb5'
Submodule 'pyca.cryptography' (https://github.com/pyca/cryptography.git) registered for path 'pyca-cryptography'
Cloning into 'boringssl'...
Submodule path 'roms/edk2/CryptoPkg/Library/OpensslLib/openssl/boringssl': checked out '2070f8ad9151dc8f3a73bffaa146b5e6937a583f'
Cloning into 'krb5'...
Submodule path 'roms/edk2/CryptoPkg/Library/OpensslLib/openssl/krb5': checked out 'b9ad6c49505c96a088326b62a52568e3484f2168'
Cloning into 'pyca-cryptography'...
Submodule path 'roms/edk2/CryptoPkg/Library/OpensslLib/openssl/pyca-cryptography': checked out '09403100de2f6f1cdd0d484dcb8e620f1c335c8f'
Cloning into 'roms/ipxe'...
Submodule path 'roms/ipxe': checked out 'de4565cbe76ea9f7913a01f331be3ee901bb6e17'
Cloning into 'roms/openbios'...
Submodule path 'roms/openbios': checked out 'c79e0ecb84f4f1ee3f73f521622e264edd1bf174'
Cloning into 'roms/openhackware'...
Submodule path 'roms/openhackware': checked out 'c559da7c8eec5e45ef1f67978827af6f0b9546f5'
Cloning into 'roms/opensbi'...
Submodule path 'roms/opensbi': checked out 'ce228ee0919deb9957192d723eecc8aaae2697c6'
Cloning into 'roms/qemu-palcode'...
Submodule path 'roms/qemu-palcode': checked out 'bf0e13698872450164fa7040da36a95d2d4b326f'
Cloning into 'roms/seabios'...
Submodule path 'roms/seabios': checked out 'a5cab58e9a3fb6e168aba919c5669bea406573b4'
Cloning into 'roms/seabios-hppa'...
Submodule path 'roms/seabios-hppa': checked out '0f4fe84658165e96ce35870fd19fc634e182e77b'
Cloning into 'roms/sgabios'...
Submodule path 'roms/sgabios': checked out 'cbaee52287e5f32373181cff50a00b6c4ac9015a'
Cloning into 'roms/skiboot'...
Submodule path 'roms/skiboot': checked out '261ca8e779e5138869a45f174caa49be6a274501'
Cloning into 'roms/u-boot'...
Submodule path 'roms/u-boot': checked out 'd3689267f92c5956e09cc7d1baa4700141662bff'
Cloning into 'roms/u-boot-sam460ex'...
Submodule path 'roms/u-boot-sam460ex': checked out '60b3916f33e617a815973c5a6df77055b2e3a588'
Cloning into 'slirp'...
Submodule path 'slirp': checked out '126c04acbabd7ad32c2b018fe10dfac2a3bc1210'
Cloning into 'tests/fp/berkeley-softfloat-3'...
Submodule path 'tests/fp/berkeley-softfloat-3': checked out 'b64af41c3276f97f0e181920400ee056b9c88037'
Cloning into 'tests/fp/berkeley-testfloat-3'...
Submodule path 'tests/fp/berkeley-testfloat-3': checked out '5a59dcec19327396a011a17fd924aed4fec416b3'
Cloning into 'ui/keycodemapdb'...
Submodule path 'ui/keycodemapdb': checked out '6b3d716e2b6472eb7189d3220552280ef3d832ce'
Switched to a new branch 'test'
6e270bf linux-user: Support gdb 'qOffsets' query for ELF

=== OUTPUT BEGIN ===
ERROR: Author email address is mangled by the mailing list
#2: 
Author: Josh Kunz via Qemu-devel <qemu-devel@nongnu.org>

total: 1 errors, 0 warnings, 8 lines checked

Commit 6e270bf43044 (linux-user: Support gdb 'qOffsets' query for ELF) has style problems, please review.  If any of these errors
are false positives report them to the maintainer, see
CHECKPATCH in MAINTAINERS.
=== OUTPUT END ===

Test command exited with code: 1


The full log is available at
http://patchew.org/logs/20190816233422.16715-1-jkz@google.com/testing.checkpatch/?type=message.
---
Email generated automatically by Patchew [https://patchew.org/].
Please send your feedback to patchew-devel@redhat.com
Laurent Vivier Aug. 26, 2019, 8:29 a.m. UTC | #2
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
Sam Eiderman via Qemu-devel Sept. 3, 2019, 7:19 p.m. UTC | #3
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
>
Laurent Vivier Sept. 4, 2019, 5:23 a.m. UTC | #4
Le 03/09/2019 à 21:19, Josh Kunz a écrit :
> 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
> 

Thank you for the details.

Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Philippe Mathieu-Daudé Sept. 5, 2019, 10:54 a.m. UTC | #5
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
>>
Laurent Vivier Sept. 10, 2019, 8:23 a.m. UTC | #6
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(+)
> 
> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index 3365e192eb..ceac035208 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -2380,6 +2380,8 @@ static void load_elf_image(const char *image_name, int image_fd,
>      }
>  
>      info->load_bias = load_bias;
> +    info->code_offset = load_bias;
> +    info->data_offset = load_bias;
>      info->load_addr = load_addr;
>      info->entry = ehdr->e_entry + load_bias;
>      info->start_code = -1;
> 

Applied to my linux-user branch.

Thanks,
Laurent

Patch
diff mbox series

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 3365e192eb..ceac035208 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -2380,6 +2380,8 @@  static void load_elf_image(const char *image_name, int image_fd,
     }
 
     info->load_bias = load_bias;
+    info->code_offset = load_bias;
+    info->data_offset = load_bias;
     info->load_addr = load_addr;
     info->entry = ehdr->e_entry + load_bias;
     info->start_code = -1;