Bug#767323: LTO not working: File format not recognized

[Benjamin Kay]

TL;DR The problem appears to be related to binutils and not clang.


I am having the same problem as the submitter with Clang 3.5.0-9.  Compiling 
the following simple hello world program:

#include iostream

int main()
{
  std::cout  Hello World\n;
  return 0;
}

$ clang++ -flto -c hello.cpp
$ clang++ -v -flto hello.o -o hello
Debian clang version 3.5.0-9 (tags/RELEASE_350/final) (based on LLVM 3.5.0) 


Target: x86_64-pc-linux-gnu 


Thread model: posix 


Found candidate GCC installation: /usr/bin/../lib/gcc/i586-linux-gnu/4.8


Found candidate GCC installation: /usr/bin/../lib/gcc/i586-linux-gnu/4.8.4
Found candidate GCC installation: /usr/bin/../lib/gcc/i586-linux-gnu/4.9
Found candidate GCC installation: /usr/bin/../lib/gcc/i586-linux-gnu/4.9.2
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.7
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.7.4
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8.4
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.9.2
Found candidate GCC installation: /usr/lib/gcc/i586-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/i586-linux-gnu/4.8.4
Found candidate GCC installation: /usr/lib/gcc/i586-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/i586-linux-gnu/4.9.2
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.2
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.9
Candidate multilib: .;@m64
Selected multilib: .;@m64
 /usr/bin/ld --hash-style=both --build-id --eh-frame-hdr -m elf_x86_64 
-dynamic-linker /lib64/ld-linux-x86-64.so.2 -o hello 
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu/crt1.o 
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu/crti.o 
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.9/crtbegin.o 
-L/usr/bin/../lib/gcc/x86_64-linux-gnu/4.9 
-L/usr/bin/../lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu 
-L/lib/x86_64-linux-gnu -L/lib/../lib64 -L/usr/lib/x86_64-linux-gnu 
-L/usr/bin/../lib/gcc/x86_64-linux-gnu/4.9/../../.. 
-L/usr/lib/llvm-3.5/bin/../lib -L/lib -L/usr/lib -plugin 
/usr/lib/llvm-3.5/bin/../lib/LLVMgold.so -plugin-opt=mcpu=x86-64 hello.o 
-lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc 
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.9/crtend.o 
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.9/../../../x86_64-linux-gnu/crtn.o
hello.o: file not recognized: File format not recognized
clang: error: linker command failed with exit code 1 (use -v to see invocation)

It appears that the default linker is not the gold linker.

$ ls -l /usr/bin/ld*
lrwxrwxrwx 1 root root   6 Dec 25 16:33 /usr/bin/ld - ld.bfd
-rwxr-xr-x 1 root root 1076192 Dec 19 13:30 /usr/bin/ld.bfd
-rwxr-xr-x 1 root root5388 Nov  6 15:12 /usr/bin/ldd
-rwxr-xr-x 1 root root 2642264 Dec 19 13:30 /usr/bin/ld.gold

The following workaround fixed the problem for me.

$ sudo rm /usr/bin/ld
$ sudo ln -s ld.gold /usr/bin/ld
$ clang++ -flto hello.o -o hello
$ ./hello
Hello World

Perhaps this bug should be reassigned to binutils.

$ dpkg -S /usr/bin/ld
binutils: /usr/bin/ld 
$ dpkg -S /usr/bin/ld.gold
binutils: /usr/bin/ld.gold


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Bug#767323: LTO not working: File format not recognized

[Eduard Bloch]

Package: clang-3.6
Version: 1:3.6~svn218612-1
Severity: normal

Hi,

I am trying to enable link time optimization with clang++. I have a
vague memory of having used it before with 3.4 or 3.5 so I tried again
and nope, doesn't work anymore:

$ clang++-3.6 -flto build/CMakeFiles/CMakeTmp/testCXXCompiler.cxx
/tmp/testCXXCompiler-be6578.o: file not recognized: File format not recognized
clang: error: linker command failed with exit code 1 (use -v to see invocation)
$ cat build/CMakeFiles/CMakeTmp/testCXXCompiler.cxx
#ifndef __cplusplus
# error The CMAKE_CXX_COMPILER is set to a C compiler
#endif
int main(){return 0;}

Adding -v flag:

Debian clang version 3.6.0-svn218612-1 (trunk) (based on LLVM 3.6.0)
Target: x86_64-pc-linux-gnu
Thread model: posix
Found candidate GCC installation: /usr/bin/../lib/gcc/i586-linux-gnu/4.7
Found candidate GCC installation: /usr/bin/../lib/gcc/i586-linux-gnu/4.7.4
Found candidate GCC installation: /usr/bin/../lib/gcc/i586-linux-gnu/4.8
Found candidate GCC installation: /usr/bin/../lib/gcc/i586-linux-gnu/4.8.3
Found candidate GCC installation: /usr/bin/../lib/gcc/i586-linux-gnu/4.9
Found candidate GCC installation: /usr/bin/../lib/gcc/i586-linux-gnu/4.9.1
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/3.4.6
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.0.4
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.4.6
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.4.7
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.6
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.6.4
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.7
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.7.4
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8.3
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.9.1
Found candidate GCC installation: /usr/lib/gcc/i586-linux-gnu/4.7
Found candidate GCC installation: /usr/lib/gcc/i586-linux-gnu/4.7.4
Found candidate GCC installation: /usr/lib/gcc/i586-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/i586-linux-gnu/4.8.3
Found candidate GCC installation: /usr/lib/gcc/i586-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/i586-linux-gnu/4.9.1
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/3.4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.0.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.1
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/4.9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
 /usr/lib/llvm-3.6/bin/clang -cc1 -triple x86_64-pc-linux-gnu -emit-llvm-bc 
-disable-free -disable-llvm-verifier -main-file-name testCXXCompiler.cxx 
-mrelocation-model static -mdisable-fp-elim -fmath-errno -masm-verbose 
-mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 
-target-linker-version 2.24.51.20140918 -v -dwarf-column-info -resource-dir 
/usr/lib/llvm-3.6/bin/../lib/clang/3.6.0 -internal-isystem 
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.9/../../../../include/c++/4.9 
-internal-isystem 
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.9/../../../../include/x86_64-linux-gnu/c++/4.9
 -internal-isystem 
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.9/../../../../include/x86_64-linux-gnu/c++/4.9
 -internal-isystem 
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.9/../../../../include/c++/4.9/backward 
-internal-isystem /usr/local/include -internal-isystem 
/usr/lib/llvm-3.6/bin/../lib/clang/3.6.0/include -internal-externc-isystem 
/usr/bin/../lib/gcc/x86_64-linux-gnu/4.9/include -internal-externc-isystem 
/usr/include/x86_64-linux-gnu -internal-externc-isystem /include 
-internal-externc-isystem /usr/include -fdeprecated-macro 
-fdebug-compilation-dir /home/ed/debian/dev/apt-cacher-ng -ferror-limit 19 
-fmessage-length 212 -mstackrealign -fobjc-runtime=gcc -fcxx-exceptions 
-fexceptions