c - Unable to pass additional flags to gcc through mpicc

Question

I have a C program that uses OpenMPI libraries. I am also using functions from libm and have included math.h in my program. When compiling using mpicc, like so
mpicc -lm program.c -o program.out
compilation succeeds, but linking fails, with ld unable to link libm and the following three lines of error
/usr/bin/ld: /tmp/cct0O5Yv.o: undefined reference to symbol 'log10@@GLIBC_2.2.5'
/usr/bin/ld: /lib/x86_64-linux-gnu/libm.so.6: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status

From what I understand, mpicc is just a wrapper for gcc whose job is to pass compilation and linking flags to gcc. Why is it not passing -lm to gcc? How do I make it pass additional flags to gcc? I couldn't fine anything in the man pages.

I used --showme:compiler and --showme:linker with mpicc and passed those flags to gcc along with -lm, and it generates the final executable just fine.

标签： cgccmpicompiler-flags

Answer 1

It turns out that the order of the command line arguments passed to mpicc matters. In order to make mpicc pass additional flags to gcc, place them before the source file

mpicc -lm program.c -o program.out

Flags placed after the source file will be treated as flags to the wrapper and not the "kernel" (in this case gcc).