[PATCH 1/9] [libbacktrace] Read .gnu_debugaltlink

[Ian Lance Taylor via gcc-patches]

On Tue, Dec 11, 2018 at 2:14 AM Tom de Vries <tdevries@suse.de> wrote:
>
> Read the elf file pointed at by the .gnu_debugaltlink section, and verify that
> the build id matches.
>
> 2018-11-11  Tom de Vries  <tdevries@suse.de>
>
>         * elf.c (elf_add): Add and handle with_buildid_data and
>         with_buildid_size parameters.  Handle .gnu_debugaltlink section.
>         (phdr_callback, backtrace_initialize): Add arguments to elf_add calls.
> ---



@@ -2899,6 +2918,27 @@ elf_add (struct backtrace_state *state, const
char *filename, int descriptor,
>             }
>         }
>
> +      if (!debugaltlink_view_valid
> +         && strcmp (name, ".gnu_debugaltlink") == 0)
> +       {
> +         const char *debugaltlink_data;
> +         size_t debugaltlink_name_len;
> +
> +         if (!backtrace_get_view (state, descriptor, shdr->sh_offset,
> +                                  shdr->sh_size, error_callback, data,
> +                                  &debugaltlink_view))
> +           goto fail;
> +
> +         debugaltlink_view_valid = 1;
> +         debugaltlink_data = (const char *) debugaltlink_view.data;
> +         debugaltlink_name = debugaltlink_data;
> +         debugaltlink_name_len = strnlen (debugaltlink_data, shdr->sh_size);
> +         debugaltlink_buildid_data = (debugaltlink_data
> +                                      + debugaltlink_name_len
> +                                      + 1);
> +         debugaltlink_buildid_size = shdr->sh_size - debugaltlink_name_len - 1;
> +       }
> +

This doesn't look quite right.  debugaltlink_buildid_size is unsigned.
If there is some misunderstanding of the format it's possible for
strnlen to return shdr->sh_size.  If it does,
debugaltlink_buildid_size will be set to a very large value.


> +  if (debugaltlink_name != NULL)
> +    {
> +      int d;
> +
> +      d = elf_open_debugfile_by_debuglink (state, filename, debugaltlink_name,
> +                                          0, error_callback, data);
> +      if (d >= 0)
> +       {
> +         int ret;
> +
> +         ret = elf_add (state, filename, d, base_address, error_callback, data,
> +                        fileline_fn, found_sym, found_dwarf, 0, 1,
> +                        debugaltlink_buildid_data, debugaltlink_buildid_size);
> +         backtrace_release_view (state, &debugaltlink_view, error_callback,
> +                                 data);
> +         debugaltlink_view_valid = 0;
> +         if (ret < 0)
> +           {
> +             backtrace_close (d, error_callback, data);
> +             return ret;
> +           }
> +       }
> +      else
> +       {
> +         error_callback (data,
> +                         "Could not open .gnu_debugaltlink", 0);
> +         /* Don't goto fail, but try continue without the info in the
> +            .gnu_debugaltlink.  */
> +       }
> +    }

The strings passed to error_callback always start with a lowercase
letter (unless they start with something like ELF) because the
callback will most likely print them with some prefix.

More seriously, we don't call error_callback in any cases that
correspond to this.  We just carry on.  Is there any reason to call
error_callback here?

Ian