[PATCH 0/3] Make glibc build with LLD

[Fāng-ruì Sòng]

On Mon, Dec 28, 2020 at 1:50 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Mon, Dec 28, 2020 at 1:45 PM Fangrui Song <maskray@google.com> wrote:
> >
> > On 2020-12-28, H.J. Lu wrote:
> > >On Mon, Dec 28, 2020 at 11:49 AM Fangrui Song via Libc-alpha
> > ><libc-alpha@sourceware.org> wrote:
> > >>
> > >> I sent the first two in April. Resending in a patch series to be
> > >> clearer.
> > >>
> > >>   install: Replace scripts/output-format.sed with objdump -f
> > >>
> > >> replaced https://sourceware.org/pipermail/libc-alpha/2020-April/112733.html
> > >> by leveraging objdump -f.
> > >>
> > >> With this patch series (available in https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/maskray/lld),
> > >> `make` with ld pointing to ld.lld (LLVM linker) works.
> > >
> > >I tried your branch with "LLD 11.0.0 (compatible with GNU linkers)" on
> > >Fedora 33/x86-64,
> > >"make check" generated:
> > >
> > >make[4]: *** [../Makerules:767:
> > >/export/users/hjl/build/gnu/tools-build/glibc-gitlab-lld/build-x86_64-linux/elf/tst-tlsmod2.so]
> > >Error 1
> > >make[4]: *** [../Makerules:767:
> > >/export/users/hjl/build/gnu/tools-build/glibc-gitlab-lld/build-x86_64-linux/elf/tst-tlsmod4.so]
> > >Error 1
> > >make[4]: *** [../Makerules:767:
> > >/export/users/hjl/build/gnu/tools-build/glibc-gitlab-lld/build-x86_64-linux/elf/tst-absolute-sym-lib.so]
> > >Error 1
> > >make[4]: *** [../Makerules:767:
> > >/export/users/hjl/build/gnu/tools-build/glibc-gitlab-lld/build-x86_64-linux/elf/tst-absolute-zero-lib.so]
> > >Error 1
> > >make[4]: *** [../Makerules:767:
> > >/export/users/hjl/build/gnu/tools-build/glibc-gitlab-lld/build-x86_64-linux/elf/tst-tlsmod6.so]
> > >Error 1
> > >make[4]: *** [../Makerules:767:
> > >/export/users/hjl/build/gnu/tools-build/glibc-gitlab-lld/build-x86_64-linux/elf/tst-tlsmod5.so]
> > >Error 1
> > >make[4]: *** [../Rules:226:
> > >/export/users/hjl/build/gnu/tools-build/glibc-gitlab-lld/build-x86_64-linux/elf/tst-audit16]
> > >Error 1
> > >make[4]: *** [../Rules:226:
> > >/export/users/hjl/build/gnu/tools-build/glibc-gitlab-lld/build-x86_64-linux/elf/tst-audit14]
> > >Error 1
> > >make[4]: *** [../Rules:226:
> > >/export/users/hjl/build/gnu/tools-build/glibc-gitlab-lld/build-x86_64-linux/elf/tst-audit15]
> > >Error 1
> > >make[4]: *** [../Rules:226:
> > >/export/users/hjl/build/gnu/tools-build/glibc-gitlab-lld/build-x86_64-linux/elf/tst-tls1]
> > >Error 1
> > >make[4]: *** [../Rules:226:
> > >/export/users/hjl/build/gnu/tools-build/glibc-gitlab-lld/build-x86_64-linux/elf/ifuncmain5]
> > >Error 1
> > >make[4]: *** [../Rules:226:
> > >/export/users/hjl/build/gnu/tools-build/glibc-gitlab-lld/build-x86_64-linux/elf/ifuncmain1]
> > >Error 1
> > >make[3]: *** [Makefile:479: elf/tests] Error 2
> > >
> > >with error messages, like
> > >
> > >ld: error: /export/users/hjl/build/gnu/tools-build/glibc-gitlab-lld/build-x86_64-linux/elf/tst-tlsmod2.os
> > >has an STT_TLS symbol but doesn't have an SHF_TLS section
> > >ld: error: /export/users/hjl/build/gnu/tools-build/glibc-gitlab-lld/build-x86_64-linux/elf/tst-tlsmod4.os
> > >has an STT_TLS symbol but doesn't have an SHF_TLS section
> >
> > tst-tls* tests appear to be similar to .tls_common which looks very
> > obsoleted and not supported by Clang. I don't think ifuncmain* or
> > tst-audit* matters for typical usage (most users) but I can take a look.
>
> "make check" should be clean on Fedora 33/x86-64.
>
> > >When glibc is configured with --enable-static-pie, I got
> > >
> > >[hjl@gnu-skx-1 build-x86_64-linux]$ ./elf/ldconfig
> > >Segmentation fault (core dumped)
> > >[hjl@gnu-skx-1 build-x86_64-linux]$
> > >
> > >You need to fix lld first and give the working lld a proper version so that
> > >configure can check it.
> >
> > I cherry picked "Make _dl_relocate_static_pie return an int indicating whether it applied relocs."
> > in google/grte/v5-2.27/master, which has fixed the issue.
>
> Why isn't it needed for ld?
>
> --
> H.J.

"Make _dl_relocate_static_pie return an int indicating whether it
applied relocs." makes glibc build with both GNU ld and LLD.
Without the commit, elf/ldconfig segfaults with LLD but works with GNU
ld because the code relies on the undefined weak
__rela_iplt_start/__rela_iplt_end to be null.

% ld.bfd  --verbose | grep rela_iplt_start
      PROVIDE_HIDDEN (__rela_iplt_start = .);
% ld.bfd -pie --verbose | grep rela_iplt_start
% ld.bfd -shared --verbose | grep rela_iplt_start

I don't think this justifies a different behavior in ld.