ld.lld: relocation R_RISCV_ALIGN requires unimplemented linker relaxation; recompile with -mno-relax

[berolinux]

Bugzilla Link	44836
Version	unspecified
OS	Linux
Blocks	#4440
CC	@lattner,@topperc,@jrtc27,@nickdesaulniers,@lenary,@smithp35

Extended Description

Clang 10.0-rc1 on riscv64-linux (RV64IMAFDC) breaks if LTO is enabled -- apparently the correct ABI isn't passed to the linker:

$ clang -march=rv64imafdc test.c
[works perfectly, binary works]
$ clang -march=rv64imafdc -flto test.c
/usr/bin/ld: /tmp/lto-llvm-f65f95.o: can't link soft-float modules with double-float modules
/usr/bin/ld: failed to merge target specific data of file /tmp/lto-llvm-f65f95.o
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)
$ clang -march=rv64imafdc -flto -fuse-ld=lld test.c
ld.lld: error: lto.tmp: cannot link object files with different floating-point ABI
ld.lld: error: static-reloc.c:(.text+0x0): relocation R_RISCV_ALIGN requires unimplemented linker relaxation; recompile with -mno-relax
ld.lld: /builddir/build/BUILD/llvm-project-release-10.x/lld/ELF/Relocations.cpp:987: uint64_t lld::elf::{anonymous}::OffsetGetter::get(uint64_t): Assertion `pieces[i].inputOff <= off && "Relocation not in any piece"' failed.
Stack dump:
0. Program arguments: /usr/bin/ld.lld --build-id --eh-frame-hdr -m elf64lriscv -dynamic-linker /lib/ld-linux-riscv64-lp64d.so.1 -o a.out /usr/bin/../lib64/gcc/riscv64-openmandriva-linux-gnu/9.2.1/../../../../lib64/crt1.o /usr/bin/../lib64/gcc/riscv64-openmandriva-linux-gnu/9.2.1/crti.o /usr/bin/../lib64/gcc/riscv64-openmandriva-linux-gnu/9.2.1/crtbegin.o -L/usr/bin/../lib64/gcc/riscv64-openmandriva-linux-gnu/9.2.1 -L/usr/bin/../lib64/gcc/riscv64-openmandriva-linux-gnu/9.2.1/../../../../lib64 -L/usr/bin/../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/lib64/lp64d -L/usr/lib64/lp64d -L/usr/bin/../lib64/gcc/riscv64-openmandriva-linux-gnu/9.2.1/../../../../riscv64-openmandriva-linux-gnu/lib -L/usr/bin/../lib64/gcc/riscv64-openmandriva-linux-gnu/9.2.1/../../.. -L/usr/bin/../lib -L/lib -L/usr/lib -plugin /usr/bin/../lib64/LLVMgold.so /tmp/test-6791f6.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/bin/../lib64/gcc/riscv64-openmandriva-linux-gnu/9.2.1/crtend.o /usr/bin/../lib64/gcc/riscv64-openmandriva-linux-gnu/9.2.1/crtn.o
clang-10: error: unable to execute command: Segmentation fault (core dumped)
clang-10: error: linker command failed due to signal (use -v to see invocation)

[lenary]

This is a known issue. LTO is not yet supported on RISC-V fully automatically.

The short-term fix is to pass -plugin-opt=-target-abi=lp64d to your linker, so it can tell LLVM which ABI to use. We hope to do the equivalent automatically soon.

[nickdesaulniers]

We're getting quite a few reports from Linux kernel CI services that are trying to link RISC-V Linux kernels with ld.lld about this unsupported relocation type.

[lenary]

There are two parts to this issue.

1. R_RISCV_ALIGN error - LLD does not support RISC-V linker relaxations. There are patches in progress, but it's a major feature to design. Compile with -mno-relax if you want to link with LLD.

2. Invalid ABI when linking with LTO - this is not an LLD issue, this is a LLVM issue in the target configuration code. I handed this work off to someone else, but it requires invasive changes to how we configure the backend when we get a new module (As it has been requested to pass the ABI using module metadata). The workaround addresses this feature.

[nickdesaulniers]

See also: riscv-non-isa/riscv-elf-psabi-doc#183.

[MaskRay]

Closed by 6611d58 (milestone: 15.0.0)