[ppc64le] unknown relocation (18) against symbol exit #150913
Description
When cross-compiling libucontext-1.3.2 for ppc64le, I'm running into the following linker error from ld.lld:
$ CC=clang CFLAGS='--target=ppc64le-alpine-linux-musl --sysroot=/opt/cross/O2' LDFLAGS='--target=ppc64le-alpine-linux-musl --sysroot=/opt/cross/O2 -static-libgcc -fuse-ld=lld' make ARCH=ppc64le
clang -std=gnu99 -D_DEFAULT_SOURCE -fPIC -DPIC --target=ppc64le-alpine-linux-musl --sysroot=/opt/cross/O2 -Iinclude -Iarch/ppc64 -Iarch/common -Iarch/common/include -DFORCE_SOFT_FLOAT -DEXPORT_UNPREFIXED -c -o arch/ppc64/makecontext.o arch/ppc64/makecontext.c
clang -std=gnu99 -D_DEFAULT_SOURCE -fPIC -DPIC --target=ppc64le-alpine-linux-musl --sysroot=/opt/cross/O2 -Iinclude -Iarch/ppc64 -Iarch/common -Iarch/common/include -DFORCE_SOFT_FLOAT -DEXPORT_UNPREFIXED -c -o arch/ppc64/retfromsyscall.o arch/ppc64/retfromsyscall.c
clang -fPIC -DPIC --target=ppc64le-alpine-linux-musl --sysroot=/opt/cross/O2 -Iinclude -Iarch/ppc64 -Iarch/common -Iarch/common/include -DFORCE_SOFT_FLOAT -DEXPORT_UNPREFIXED -Wa,--noexecstack -c -o arch/ppc64/getcontext.o arch/ppc64/getcontext.S
clang -fPIC -DPIC --target=ppc64le-alpine-linux-musl --sysroot=/opt/cross/O2 -Iinclude -Iarch/ppc64 -Iarch/common -Iarch/common/include -DFORCE_SOFT_FLOAT -DEXPORT_UNPREFIXED -Wa,--noexecstack -c -o arch/ppc64/setcontext.o arch/ppc64/setcontext.S
clang -fPIC -DPIC --target=ppc64le-alpine-linux-musl --sysroot=/opt/cross/O2 -Iinclude -Iarch/ppc64 -Iarch/common -Iarch/common/include -DFORCE_SOFT_FLOAT -DEXPORT_UNPREFIXED -Wa,--noexecstack -c -o arch/ppc64/startcontext.o arch/ppc64/startcontext.S
clang -fPIC -DPIC --target=ppc64le-alpine-linux-musl --sysroot=/opt/cross/O2 -Iinclude -Iarch/ppc64 -Iarch/common -Iarch/common/include -DFORCE_SOFT_FLOAT -DEXPORT_UNPREFIXED -Wa,--noexecstack -c -o arch/ppc64/swapcontext.o arch/ppc64/swapcontext.S
clang -fPIC -o libucontext.so -shared -Wl,-soname,libucontext.so.1 -Wl,-z,noexecstack arch/ppc64/makecontext.o arch/ppc64/retfromsyscall.o arch/ppc64/getcontext.o arch/ppc64/setcontext.o arch/ppc64/startcontext.o arch/ppc64/swapcontext.o --target=ppc64le-alpine-linux-musl --sysroot=/opt/cross/O2 -static-libgcc -fuse-ld=lld
ld.lld: error: arch/ppc64/startcontext.o:(.text+0x20): unknown relocation (18) against symbol exit
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [Makefile:127: libucontext.so] Error 1
Using ld.mold gives a similar error, using ld.bfd makes bfd segfault.
The error is caused by Clang creating an object file with an unrecognized relocation type (0x12 == 18) from the arch/ppc64/startcontext.S assembly input:
$ clang --target=ppc64le-alpine-linux-musl -Iarch/common -Wa,--noexecstack -c -o arch/ppc64/startcontext.o arch/ppc64/startcontext.S
$ readelf -r arch/ppc64/startcontext.o
Relocation section '.rela.text' at offset 0xc8 contains 1 entry:
Offset Info Type Sym. Value Sym. Name + Addend
000000000020 000300000012 unrecognized: 12 0000000000000000 exit + 0
OTOH, GCC produces valid output:
$ /opt/cross/O2/usr/bin/ppc64le-alpine-linux-musl-gcc -Iarch/common -Wa,--noexecstack -c -o arch/ppc64/startcontext.o arch/ppc64/startcontext.S
$ readelf -r arch/ppc64/startcontext.o
Relocation section '.rela.text' at offset 0x158 contains 1 entry:
Offset Info Type Sym. Value Sym. Name + Addend
000000000020 00070000000e R_PPC64_GOT16 0000000000000000 exit + 0
This is with Clang 20 from Alpine Linux 3.22:
$ clang -v
Alpine clang version 20.1.8
Target: x86_64-alpine-linux-musl
Thread model: posix
InstalledDir: /usr/lib/llvm20/bin
Configuration file: /etc/clang20/x86_64-alpine-linux-musl.cfg
System configuration file directory: /etc/clang20
Found candidate GCC installation: /usr/lib/gcc/x86_64-alpine-linux-musl/14.2.0
Selected GCC installation: /usr/lib/gcc/x86_64-alpine-linux-musl/14.2.0
Candidate multilib: .;@m64
Selected multilib: .;@m64
Please let me know if you need any other information.