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

["Fāng-ruì Sòng via Libc-alpha" <libc-alpha@sourceware.org>]

On Mon, Aug 30, 2021 at 1:01 PM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> 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

I'll use https://sourceware.org/pipermail/libc-alpha/2021-August/130637.html
which XFAIL the two ifunc tests.