Code model should take into account pragma weak.
Code example:
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#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#pragma weak foo=_foo
void _foo(){
    printf("Arguments:\n");
}

int main(int argc, char**argv) {
    foo();
    for (int i = 0; i < argc; i++) {
        printf("%i: %s\n", i, argv[i]);
    }
    return 0;
}
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Hyper link from function call foo() doesn't work.
Open Solaris project has many such code.
For example libc has definition of pthread_spin_init in source usr/src/lib/libc/port/threads/synch.c
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#pragma weak pthread_spin_init = _pthread_spin_init
int
_pthread_spin_init(pthread_spinlock_t *lock, int pshared)
{
  ...
}
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Header file pthread.h declares:
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extern int pthread_spin_lock(pthread_spinlock_t *);
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