2.36 pre-release

[Florian Weimer]

* Paul Zimmermann:

>        Dear Florian,
>
>> > on my i5-4590 with gcc 11.3.0, I get one failure when I configure with
>> > -march=native:
>> >
>> > Summary of test results:
>> >       1 FAIL
>> >    5084 PASS
>> >      77 UNSUPPORTED
>> >      18 XFAIL
>> >       4 XPASS
>> >
>> > FAIL: elf/tst-valgrind-smoke
>> >
>> > zimmerma@tomate:/localdisk/zimmerma/glibc/build-fma$ cat elf/tst-valgrind-smoke.out 
>> > /usr/bin/valgrind
>> > /lib64/ld-linux-x86-64.so.2
>> > bin: /localdisk/zimmerma/glibc/build-fma/elf/valgrind-test
>> > ld.so: /localdisk/zimmerma/glibc/build-fma/elf/ld.so
>> 
>> Would you please check if there is output to stderr, e.g. when running
>> 
>>   make t=elf/tst-valgrind-smoke test
>> 
>> ?  It's possible that valgrind does not support everything required by
>> -march=native.
>
> ok course, here you are:
>
> zimmerma@tomate:/localdisk/zimmerma/glibc/build-fma$  make t=elf/tst-valgrind-smoke test
> ...
> ==2457609== Conditional jump or move depends on uninitialised value(s)
> ==2457609==    at 0x12A118: strcmp (strcmp-avx2.S:462)
> ==2457609==    by 0x1125B4: _dl_name_match_p (dl-misc.c:69)
> ==2457609==    by 0x10FE43: _dl_map_object (dl-load.c:1971)
> ==2457609==    by 0x122124: map_doit (rtld.c:647)
> ==2457609==    by 0x11F8C5: _dl_catch_exception (dl-error-skeleton.c:208)
> ==2457609==    by 0x11F95E: _dl_catch_error (dl-error-skeleton.c:227)
> ==2457609==    by 0x12261E: do_preload (rtld.c:822)
> ==2457609==    by 0x12340F: handle_preload_list (rtld.c:898)
> ==2457609==    by 0x12630F: dl_main (rtld.c:1857)
> ==2457609==    by 0x1217BE: _dl_sysdep_start (dl-sysdep.c:140)
> ==2457609==    by 0x1231E1: _dl_start_final (rtld.c:497)
> ==2457609==    by 0x1231E1: _dl_start (rtld.c:584)
> ==2457609==    by 0x122007: ??? (in /localdisk/zimmerma/glibc/build-fma/elf/ld.so)
> ==2457609== 

I think we need more intercepts for ld.so, similar to what was added
here for strncmp:

  iconv_open causes ld.so v2.28 and later to execute optimised strncmp
  which confuses memcheck
  <https://bugs.kde.org/show_bug.cgi?id=434764>

With some recent x86-64 changes, -march=native affects the choice of the
baseline string function implementation that gets used in ld.so, which
is why this wasn't visible before.

You also need to upgrade to get proper rseq support in valgrind (but
this isn't why this test fails).

Thanks,
Florian