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 /* This Source Code Form is subject to the terms of the Mozilla Public

  * License, v. 2.0. If a copy of the MPL was not distributed with this

  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

 /*

   A library that can be LD_PRELOAD-ed to dump a function's address on

   function entry.

  */

 #include <unistd.h>

 /**

  * When compiled with `-pg' (or even just `-p'), gcc inserts a call to

  * |mcount| in each function prologue. This implementation of |mcount|

  * will grab the return address from the stack, and write it to stdout

  * as a binary stream, creating a gross execution trace the

  * instrumented program.

  *

  * For more info on gcc inline assembly, see:

  *

  *   <http://www.ibm.com/developerworks/linux/library/l-ia.html?dwzone=linux>

  *

  */

 void

 mcount()

 {

     register unsigned int caller;

     unsigned int buf[1];

     // Grab the return address. 

     asm("movl 4(%%esp),%0"

         : "=r"(caller));

     buf[0] = caller;

     write(STDOUT_FILENO, buf, sizeof buf[0]);

 }