int
   main(int argc, char **argv) {
        void *faddr = strxfrm;
        void *paddr = (void*) ((u_int32_t)faddr & 0xfffff000);

        if(mprotect(paddr, 4096, PROT_READ|PROT_WRITE|PROT_EXEC) >= 0) {
                ((u_char *)faddr)[0] = 0xcc;
                strxfrm("foo", "", 0);
        } else
                perror("mprotect");

        exit(0);
   }

   $ ./mp
   Trace/BPT trap

The simplest answer to your question that jumps into my head is "relocations", but I'm always surprised by the everyday craziness of the C runtime and the Unix ABI, so I'm sure there's a simpler answer.