[Mesa-dev] [PATCH 1/2] util: Add utility build-id code.

[Matt Turner]

On Tue, Feb 14, 2017 at 12:43 PM, Nicholas Miell <nmiell at gmail.com> wrote:
> On 02/14/2017 12:30 PM, Chad Versace wrote:
>>
>> On Tue 14 Feb 2017, Matt Turner wrote:
>>>
>>> Provides the ability to read the .note.gnu.build-id section of ELF
>>> binaries, which is inserted by the --build-id=... flag to ld.
>>> ---
>>> configure.ac | 2 +
>>> src/util/Makefile.sources | 2 +
>>> src/util/build_id.c | 109
>>> ++++++++++++++++++++++++++++++++++++++++++++++
>>> src/util/build_id.h | 56 ++++++++++++++++++++++++
>>> 4 files changed, 169 insertions(+)
>>> create mode 100644 src/util/build_id.c
>>> create mode 100644 src/util/build_id.h
>>
>>
>>
>>> +AC_CHECK_FUNC([dl_iterate_phdr], [DEFINES="$DEFINES
>>> -DHAVE_DL_ITERATE_PHDR"])
>>
>>
>> Nice. I wasn't aware of dl_iterate_phdr(). My code for querying the
>> build-id was less slick. It used open(2) on the library, then manually
>> parsed the ElfW(Ehdr) and ElfW(Shdr) to find the build-id node.
>
>
> I also reinvented the build ID lookup wheel and just to record this
> knowledge publicly for posterity:
>
> The struct link_map l_addr field seems to corresponds to the struct
> dl_phdr_info dlpi_addr field.
>
> You can retrieve the struct link_map for a symbol by passing the
> RTLD_DL_LINKMAP flag to dladdr1() or for a library handle returned by
> dlopen() by passing RTLD_DI_LINKMAP to dlinfo().
>
> This means you can find the note section for a loaded library directly
> without having to resort to string comparisons against library names,
which
> is probably more future-proof.

That's really neat. Thanks for the information.

It doesn't look like the BSDs or musl libc support RTLD_DL_LINKMAP. In the
interest of avoiding future problems I'll stick with the string comparison
for now.
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