Minimal reproducible example:

foo.s:

global foo

section .data

foo: db "bar", 0

main.c:

#include <stdio.h>

extern char *foo;

int main() {
    puts(foo);
}

Where I’m running these commands on a 64-bit Ubuntu computer:

nasm -f elf64 foo.s
gcc main.c foo.o
./a.out

But this prints “Segmentation fault (core dumped)”.

I’ve tried a mix of -fPIC and -no-pie, but haven’t been able to get rid of the runtime segmentation fault with the combinations I’ve tried.

Running nm foo.o prints 0000000000000000 D foo, which seems correct, as the capitalized D means global data according to nm’s man page.

By compiling with -g I can step into main() and run p foo to see that gdb states that foo its address is just wrong:

$1 = 0x726162 <error: Cannot access memory at address 0x726162>