Re: [PATCH v2 3/3] configure: Allow LD to be LLD 13.0.0 or above [BZ #26558]

[Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>]

On 30/08/2021 16:52, Fāng-ruì Sòng via Libc-alpha wrote:
> On Tue, Aug 24, 2021 at 10:05 AM Fāng-ruì Sòng <maskray@google.com> wrote:
>>
>> On Sun, Aug 22, 2021 at 8:18 PM Fāng-ruì Sòng <maskray@google.com> wrote:
>>>
>>> On Tue, Aug 10, 2021 at 3:19 PM Fangrui Song <maskray@google.com> wrote:
>>>>
>>>> On 2021-08-05, Fangrui Song wrote:
>>>>> When using LLD (LLVM linker) as the linker, configure prints a confusing
>>>>> message.
>>>>>
>>>>>    *** These critical programs are missing or too old: GNU ld
>>>>>
>>>>> LLD>=13.0.0 can build glibc --enable-static-pie. (8.0.0 needs one
>>>>> workaround for -Wl,-defsym=_begin=0. 9.0.0 works with
>>>>> --disable-static-pie).
>>>>>
>>>>> With BZ #28153 (glibc bug exposed by testing with LLD) fixed,
>>>>> `make check` only has 2 more failures with LLD than with GNU ld:
>>>>> BZ #28154 (LLD follows the PowerPC port of GNU ld for ifunc by
>>>>> placing IRELATIVE relocations in .rela.dyn).
>>>>> The set of dynamic symbols is the same with GNU ld and LLD,
>>>>> modulo unused SHN_ABS version node symbols.
>>>>>
>>>>> For comparison, gold does not support --enable-static-pie
>>>>> yet (--no-dynamic-linker is unsupported BZ #22221), yet
>>>>> has 6 failures more than LLD. gold linked libc.so has
>>>>> larger .dynsym differences with GNU ld and LLD
>>>>> (ISTM non-default version symbols are changed to default versions
>>>>> by a version script).
>>>>>
>>>>> ---
>>>>>
>>>>> I identified the lack of support of
>>>>>
>>>>> * version script on non-default version symbols
>>>>> * copy relocations on non-default version symbols
>>>>>
>>>>> in an earlier snapshot of LLD 13.0.0 and fixed them.
>>>>> The functionality of the LLD linked libc.so and ld.so looks pretty good.
>>>>> ---
>>>>> configure    | 77 +++++++++++++++++++++++++++++++++++++++++++++++++---
>>>>> configure.ac | 20 ++++++++++----
>>>>> 2 files changed, 88 insertions(+), 9 deletions(-)
>>>>
>>>> Ping:)
>>>>
>>>> (The code/test hasn't been changed since v1.
>>>>   v2 just added BZ numbers.)
>>>>
>>>> x86-64 only 2 more ifunc FAIL which tickle some weak point of ifunc implementation.
>>>>
>>>> aarch64 `make-check` is fully on par with GNU ld.
>>>>    (https://sourceware.org/pipermail/libc-alpha/2021-August/130040.html)
>>>
>>> Ping^2
>>>
>>> ("elf: Replace .tls_common with .tbss definition [BZ #28152]" has been
>>> subsumed into a tls-macros.h removal patch.)
>>
>> This is now the only needed commit.
>>
>> aarch64 and ppc64le look on par.
>> x86-64 just has 2 more FAIL due to ld.so's intrinsic lack of ifunc robustness.
> 
> 
> Ping^4. I'll push if nobody objects.

H.J has raised some objections and referenced BZ#28218 [1].  Are the
two tests still occurring with lld? If it were the case I think we
should at least xfailing then by returning FAIL_UNSUPPORTED if lld
is being used the linker.

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=28218