[Bug dynamic-link/28154] New: [test] sysdeps/x86/tst-ifunc-isa-* lazy binding failure with ld.lld

["i at maskray dot me" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=28154

            Bug ID: 28154
           Summary: [test] sysdeps/x86/tst-ifunc-isa-* lazy binding
                    failure with ld.lld
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: i at maskray dot me
  Target Milestone: ---

Extracted from
https://sourceware.org/pipermail/libc-alpha/2021-July/129450.html

To build LLD 13.0.0:

# https://github.com/llvm/llvm-project/ origin/release/13.x
cmake -H. -Bout/release -G Ninja -DCMAKE_BUILD_TYPE=Release
-DLLVM_ENABLE_PROJECTS='clang;lld'
ninja -C out/release lld

I use
sudo ln -sf $PWD/out/release/bin/lld /usr/local/bin/ld
to ensure the glibc build system definitely picks ld => lld
(messing around with LDFLAGS=-fuse-ld=lld may work as well)


`make check` says sysdeps/x86/tst-ifunc-isa-* fail.
The tests work with LD_BIND_NOW=1.

I debugged a bit. ld.lld and GNU ld place IRELATIVE differently. IIUC some
ports of GNU ld use .rela.dyn and behave similar to ld.lld.

The tests happen to work with GNU ld because the IRELATIVE for foo_ifunc
is placed after JUMP_SLOT in .repa.plt.  The test needs to call
__x86_get_cpuid_feature_leaf which is defined in a different TU. IMHO
such ifunc does not guaranteed to work.

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