This page provides information about the different phases of compiling and running a C (or C++) program and tools that can be used to examine the results of these different phases.

The different phases examined below are:

1. the preprocessor (expands #'s)
2. the compiler (produces .s or .o files)
3. the assembler (produces .o files from .s files)
4. the link editor (produces a.out files)
5. the runtime linker (loads and links shared libraries used by a.out)

The different tools used to examine compiler output include:

• objdump
• readelf
• gdb (the disass command in particular)
• nm
• ldd
• file
• hexdump, hexedit, strings

More information and examples using some of these tools to examine .o and a.out files (hexdump, strings, objdump, gdb).

---

The following program is used as an example below (it is also available in ~newhall/public/cs75/compilecycle/ with a Makefile for building .o and executable files):

// simple.c:
#include <unistd.h>
#define MAX  10
int foo(int y);

main() {
  int x, i;
  char buf[10];

  for(i=0; i < MAX; i++) {
    x = foo(i);
    // a crazy way to print to stdout
    sprintf(buf, "%d", x);
    write(0, buf, strlen(buf));
    buf[0] = '\n';
    write(0, buf, 1);
  }
}
int foo(int y) {
  return y*y;
}