clang failed to link binaries when -flto option is used.

[Deng Yao]

clang-3.3/3.4 cannot link a simple binary if -flto option is used (in order to enable link-time-optimization), probably due to incorrect packaging of LLVMgold.so which can be found in /usr/lib/llvm-<version>/lib/LLVMgold.so, however the gold linker only searchs /usr/lib for LLVMgold.so

The following command clearly shows the problem:
user@ubuntu:/tmp$ echo 'int main() {}' | clang -xc - -flto -v
Ubuntu clang version 3.4-1ubuntu1 (trunk) (based on LLVM 3.4)
Target: x86_64-pc-linux-gnu
Thread model: posix
 "/usr/bin/clang" -cc1 -triple x86_64-pc-linux-gnu -emit-llvm-bc -disable-free -disable-llvm-verifier -main-file-name - -mrelocation-model static -mdisable-fp-elim -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -target-linker-version 2.23.52.20130727 -v -resource-dir /usr/bin/../lib/clang/3.4 -internal-isystem /usr/local/include -internal-isystem /usr/bin/../lib/clang/3.4/include -internal-isystem /usr/include/clang/3.4/include/ -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /usr/include -fdebug-compilation-dir /tmp -ferror-limit 19 -fmessage-length 105 -mstackrealign -fobjc-runtime=gcc -fobjc-default-synthesize-properties -fdiagnostics-show-option -fcolor-diagnostics -backend-option -vectorize-loops -o /tmp/--5RQxuk.o -x c -
clang -cc1 version 3.4 based upon LLVM 3.4 default target x86_64-pc-linux-gnu
ignoring nonexistent directory "/usr/bin/../lib/clang/3.4/include"
ignoring duplicate directory "/usr/include/x86_64-linux-gnu"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/include/clang/3.4/include
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
 "/usr/bin/ld" -z relro --hash-style=gnu --build-id --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o a.out /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crt1.o /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crti.o /usr/lib/gcc/x86_64-linux-gnu/4.8/crtbegin.o -L/usr/lib/gcc/x86_64-linux-gnu/4.8 -L/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu -L/lib/x86_64-linux-gnu -L/lib/../lib64 -L/usr/lib/x86_64-linux-gnu -L/usr/lib/gcc/x86_64-linux-gnu/4.8/../../.. -L/lib -L/usr/lib -plugin /usr/bin/../lib/LLVMgold.so -plugin-opt=mcpu=x86-64 /tmp/--5RQxuk.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/x86_64-linux-gnu/4.8/crtend.o /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crtn.o
/usr/bin/ld: /usr/bin/../lib/LLVMgold.so: error loading plugin: /usr/bin/../lib/LLVMgold.so: cannot open shared object file: No such file or directory
clang: error: linker command failed with exit code 1 (use -v to see invocation)

Ubuntu release 13.10

BTW, there are other issues related to link-time-optimization on ubuntu, probably upstream bugs.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Rolf Timmermans (rolftimmermans)]

Having the same problem. Is there a temporary workaround for this that makes lto work?

[Ivan Kozik (ludios)]

I ran into this and my workaround was:

ln -sf /usr/lib/llvm-3.4/lib/LLVMgold.so /usr/lib/LLVMgold.so
echo /usr/lib/llvm-3.4/lib >> /etc/ld.so.conf
ldconfig

I also had to add -B/usr/lib/gold-ld to my clang options to get it to use /usr/bin/ld.gold instead of /usr/bin/ld.bfd

(-B takes a directory containing ld, not a path to a linker!)

[mjau (mjau-deactivatedaccount)]

This still happens with clang 3.7 in Ubuntu 15.10.

[Roger Binns (ubuntu-rogerbinns)]

And clang 3.8 in Ubuntu 16.04.

[Sebastian Ramacher (s-ramacher)]

Also affects clang 3.9 in yakkety.

[Sylvestre Ledru (sylvestre)]

Just install llvm-3.9-dev