Re: [PATCH v2 2/2] Make a "gdb" dprintf that tells us load addresses

[Daniel Kiper]

On Wed, Nov 03, 2021 at 02:22:07PM -0400, Robbie Harwood wrote:
> From: Peter Jones <pjones@redhat.com>
>
> Add a grub_dprintf() call during platform init and during module loading
> that tells us the virtual addresses of the .text and .data sections of
> grub-core/kernel.exec and any modules it loads.
>
> Specifically, it displays them in the gdb "add-symbol-file" syntax, with
> the presumption that there's a variable $grubdir that reflects the path
> to any such binaries.

Could you tell us why this thing has to be displayed as a part of debug
messages? Could you create a separate command which would do the same?

Additionally, I think this kind of information should not be printed if
the lockdown/UEFI Secure Boot is enforced.

> Signed-off-by: Peter Jones <pjones@redhat.com>
> [rharwood@redhat.com: remove custom function, adjust commit message]
> Signed-off-by: Robbie Harwood <rharwood@redhat.com>
> ---
>  grub-core/kern/dl.c       | 50 +++++++++++++++++++++++++++++++++++++++
>  grub-core/kern/efi/efi.c  |  4 ++--
>  grub-core/kern/efi/init.c | 26 +++++++++++++++++++-
>  include/grub/efi/efi.h    |  2 +-
>  4 files changed, 78 insertions(+), 4 deletions(-)
>
> diff --git a/grub-core/kern/dl.c b/grub-core/kern/dl.c
> index 6a52de168..a5def4ea3 100644
> --- a/grub-core/kern/dl.c
> +++ b/grub-core/kern/dl.c
> @@ -447,6 +447,23 @@ grub_dl_find_section (Elf_Ehdr *e, const char *name)
>        return s;
>    return NULL;
>  }
> +static long
> +grub_dl_find_section_index (Elf_Ehdr *e, const char *name)
> +{
> +  Elf_Shdr *s;
> +  const char *str;
> +  unsigned i;
> +
> +  s = (Elf_Shdr *) ((char *) e + e->e_shoff + e->e_shstrndx * 
> e->e_shentsize);
> +  str = (char *) e + s->sh_offset;
> +
> +  for (i = 0, s = (Elf_Shdr *) ((char *) e + e->e_shoff);
> +       i < e->e_shnum;
> +       i++, s = (Elf_Shdr *) ((char *) s + e->e_shentsize))
> +    if (grub_strcmp (str + s->sh_name, name) == 0)
> +      return (long)i;
> +  return -1;
> +}
>
>  /* Me, Vladimir Serbinenko, hereby I add this module check as per new
>     GNU module policy. Note that this license check is informative only.
> @@ -607,6 +624,37 @@ grub_dl_relocate_symbols (grub_dl_t mod, void *ehdr)
>
>    return GRUB_ERR_NONE;
>  }
> +static void
> +grub_dl_print_gdb_info (grub_dl_t mod, Elf_Ehdr *e)
> +{
> +  void *text, *data = NULL;
> +  long idx;
> +
> +  idx = grub_dl_find_section_index (e, ".text");
> +  if (idx < 0)
> +    return;
> +
> +  text = grub_dl_get_section_addr (mod, idx);
> +  if (!text)
> +    return;
> +
> +  idx = grub_dl_find_section_index (e, ".data");
> +  if (idx >= 0)
> +    data = grub_dl_get_section_addr (mod, idx);
> +
> +  if (data)
> +    grub_dprintf ("gdb", "add-symbol-file \\\n"
> +               "/usr/lib/debug/usr/lib/grub/%s-%s/%s.debug "
> +               "\\\n %p -s .data %p\n",
> +               GRUB_TARGET_CPU, GRUB_PLATFORM,
> +               mod->name, text, data);
> +  else
> +    grub_dprintf ("gdb", "add-symbol-file \\\n"
> +               "/usr/lib/debug/usr/lib/grub/%s-%s/%s.debug "

No, paths cannot be hard coded like here. At least part of them should be
taken from the configure.

Daniel