Re: [Qemu-devel] [PATCH] linux-user: Support gdb 'qOffsets' query for ELF

[Josh Kunz via Qemu-devel <qemu-devel@nongnu.org>]

+cc: riku.voipio@iki.fi, I typoed the email on the first go.

On Fri, Aug 16, 2019 at 4:34 PM Josh Kunz <jkz@google.com> wrote:

> 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;
> --
> 2.23.0.rc1.153.gdeed80330f-goog
>
>