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 (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.

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>

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 43c16a846d33ac066c8f0a7aea37c2c74f17d67c..f6693e57609889e05dadbc84482daa77fce8103a 100644 (file)
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -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;