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.
See PR ld/13302. lld should implement the same behavior.
(In reply to H.J. Lu from comment #1) > See PR ld/13302. lld should implement the same behavior. I think the GNU ld PowerPC (ld.lld) behavior (IRELATIVE in .rela.dyn) makes more sense. IRELATIVE relocations are eagerly resolved, so .rela.dyn is better than .rela.plt . .rela.plt should only have JUMP_SLOT. To make PR ld/13302 work, ld.so can pause at IRELATIVE in .rela.dyn and start applying .rela.plt (I use the section names for simplicity. Impl should use dynamic tags DT_RELA/DT_JMPREL.)
(In reply to Fangrui Song from comment #2) > > To make PR ld/13302 work, ld.so can pause at IRELATIVE in .rela.dyn and > start applying .rela.plt > This requires both linker and ld.so changes. The PR ld/13302 linker change doesn't require ld.so change.
The master branch has been updated by Fangrui Song <maskray@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=224edada607ebc6aaa1aadaae423128fae7880df commit 224edada607ebc6aaa1aadaae423128fae7880df Author: Fangrui Song <maskray@google.com> Date: Mon Aug 30 13:59:33 2021 -0700 configure: Allow LD to be LLD 13.0.0 or above [BZ #26558] 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). XFAIL two tests sysdeps/x86/tst-ifunc-isa-* which have the BZ #28154 issue (LLD follows the PowerPC port of GNU ld for ifunc by placing IRELATIVE relocations in .rela.dyn, triggering a glibc ifunc fragility). 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 (non-default version symbols are changed to default versions by a version script BZ #28196).
Does 63b31c05a8a901562ba9228d254156e436682c1b improve the ifunc handling in this scenario?