.gitignore

/a.o
/b.o
/c.o
/program

a.cpp

inline int f() {
    asm(
            ".weak abc\n"
            "abc: nop\n"
            ".pushsection CUSTOM, \"aw\"\n"
            ".quad abc\n"
            ".quad 0x0123456789abcdef\n"
            ".popsection"
       );
    return 1;
}
int g() { return f(); }

b.cpp

inline int f() {
    asm(
            ".weak abc\n"
            "abc: nop\n"
            ".pushsection CUSTOM, \"aw\"\n"
            ".quad abc\n"
            ".quad 0x0123456789abcdef\n"
            ".popsection"
       );
    return 1;
}
int h() { return f(); }

build.sh

#!/bin/bash
set -e -x
g++ -fPIC a.cpp -c -o a.o
g++ -fPIC b.cpp -c -o b.o
ld -relocatable a.o b.o -o c.o
g++ main.cpp c.o -o program
./program
exit
objdump -D --reloc c.o
objdump -D --reloc a.o

main.cpp

#include<stdio.h>
int g();
int h();
int main(){
    printf("%d %d\n", g(), h());
}