Override Shared Library Function Calls

Makefile

override.so:override.c
        gcc -shared -fPIC $^ -o $@

test:
        LD_PRELOAD=$(PWD)/override.so glxgears

clean:
        rm $(PWD)/override.so

override.c

// This will take OpenGL calls to draw a 3D vertex
// and print the X coordinate.
//
// Run `make` and `make test` to see it happen.

#include <stdio.h>

void glVertex3f(float x, float y, float z){
  printf("%.6f", x);
  return;
}