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linux-user: Support gdb 'qOffsets' query for ELF 

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 (978efd6aac),
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.

http://sourceware.org/gdb/onlinedocs/gdb/General-Query-Packets.html#index-qOffsets-packet

Buglink: https://bugs.launchpad.net/qemu/+bug/1528239
Signed-off-by: Josh Kunz <jkz@google.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190816233422.16715-1-jkz@google.com>
[lv: added link to documentation]
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
master
Josh Kunz 2019-08-16 16:34:22 -07:00 committed by Laurent Vivier
parent 0b689da375
commit dc12567a53
1 changed files with 2 additions and 0 deletions
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2
linux-user/elfload.c
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@ -2403,6 +2403,8 @@ 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;