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 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.