linking OpenMP statically with GCC - gcc

Question

Given the following file print.cpp
#include <stdio.h>
int main() {
printf("asdf\n");
}
I can link this statically like this
g++ -static print.cpp
or like this
g++ -static-libgcc -Wl,-Bstatic -lc print.cpp -o print
But now let's add a little OpenMP and call the file print_omp.cpp
#include <omp.h>
#include <stdio.h>
int main() {
printf("%d\n", omp_get_num_threads());
}
I can link this statically like this (I checked it with ldd)
g++ -fopenmp -static print_omp.cpp
However, this does not work
g++ -fopenmp -static-libgcc -Wl,-Bstatic -lc print_omp.cpp -o print
I have tried various combinations of -Wl,--whole-archive -lpthread -Wl,--no-whole-archive and -lgomp -lpthread but no luck (I get various problems linking to pthreads). Can someone explain how I can do this without using the -static option?
GCC says
On glibc-based systems, OpenMP enabled applications cannot be statically linked due to limitations of the underlying pthreads-implementation
However, since g++ -fopenmp -static print_omp.cpp works just fine this does not make sense to me.
Edit:
I figured this out. The library GOMP comes with GCC whereas pthreads and libc come from GLIBC. So I can link GOMP statically like this
ln -s `g++ -print-file-name=libgomp.a`
g++ foo.cpp -static-libgcc -static-libstdc++ -L. -o foo -O3 -fopenmp
ldd shows
linux-vdso.so.1 => (0x00007fff71dbe000)
libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fc231923000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fc23155c000)
/lib64/ld-linux-x86-64.so.2 (0x00007fc231b5c000)
However, if I the try this
ln -s `g++ -print-file-name=libpthread.a`
g++ foo.cpp -static-libgcc -static-libstdc++ -L. -o foo -O3 -fopenmp
It won't link. Pthreads and libc must be linked statically together. So once I add
ln -s `g++ -print-file-name=libc.a`
g++ foo.cpp -static-libgcc -static-libstdc++ -L. -o foo -O3 -fopenmp
ldd returns
not a dynamic executable

Answer 1

I really don't get why you may want to link only libgomp statically, but having separate compilation and linking commands may help. For instance assume main.cpp contains:
#include <omp.h>
#include <stdio.h>
int main() {
#pragma omp parallel
{
printf("%d\n", omp_get_thread_num());
}
}
Then:
~/tmp$ ls
main.cpp
~/tmp$ g++ -Wall -Werror -pedantic -fopenmp main.cpp -c
~/tmp$ ls
main.cpp main.o
~/tmp$ locate libgomp.a
${SOME_PATH_TO_LIBGOMP}/libgomp.a
~/tmp$ g++ -Wall -Werror -pedantic main.o -o main.x ${SOME_PATH_TO_LIBGOMP}/libgomp.a -pthread
~/tmp$ ls
main.cpp main.o main.x
~/tmp$ ldd main.x
linux-gate.so.1 => (0xb7747000)
libstdc++.so.6 => /production/install/gnu/compiler/gcc/lib/libstdc++.so.6 (0xb765c000)
libm.so.6 => /lib/i386-linux-gnu/libm.so.6 (0xb75fa000)
libgcc_s.so.1 => /production/install/gnu/compiler/gcc/lib/libgcc_s.so.1 (0xb75de000)
libpthread.so.0 => /lib/i386-linux-gnu/libpthread.so.0 (0xb75c2000)
libc.so.6 => /lib/i386-linux-gnu/libc.so.6 (0xb7413000)
/lib/ld-linux.so.2 (0xb7748000)

Answer 2

The most clean solution I've found for this is by modifying the libgomp.spec. Mine is at /usr/local/lib64/libgomp.spec. Change the content as follow:
*link_gomp: -l:libgomp.a %{static: -ldl }