tools/reorder/mcount.c

   1 /* ***** BEGIN LICENSE BLOCK *****
   2  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
   3  *
   4  * The contents of this file are subject to the Mozilla Public License Version
   5  * 1.1 (the "License"); you may not use this file except in compliance with
   6  * the License. You may obtain a copy of the License at
   7  * http://www.mozilla.org/MPL/
   8  *
   9  * Software distributed under the License is distributed on an "AS IS" basis,
  10  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
  11  * for the specific language governing rights and limitations under the
  12  * License.
  13  *
  14  * The Original Code is ``mcount''
  15  *
  16  * The Initial Developer of the Original Code is Netscape
  17  * Communications Corp.  Portions created by the Initial Developer are
  18  * Copyright (C) 2001 the Initial Developer. All Rights Reserved.
  19  *
  20  * Contributor(s):
  21  *   Chris Waterson <waterson@netscape.com>
  22  *
  23  * Alternatively, the contents of this file may be used under the terms of
  24  * either the GNU General Public License Version 2 or later (the "GPL"), or
  25  * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
  26  * in which case the provisions of the GPL or the LGPL are applicable instead
  27  * of those above. If you wish to allow use of your version of this file only
  28  * under the terms of either the GPL or the LGPL, and not to allow others to
  29  * use your version of this file under the terms of the MPL, indicate your
  30  * decision by deleting the provisions above and replace them with the notice
  31  * and other provisions required by the GPL or the LGPL. If you do not delete
  32  * the provisions above, a recipient may use your version of this file under
  33  * the terms of any one of the MPL, the GPL or the LGPL.
  34  *
  35  * ***** END LICENSE BLOCK ***** */
  36
  37 /*
  38
  39   A library that can be LD_PRELOAD-ed to dump a function's address on
  40   function entry.
  41
  42  */
  43
  44 #include <unistd.h>
  45
  46 /**
  47  * When compiled with `-pg' (or even just `-p'), gcc inserts a call to
  48  * |mcount| in each function prologue. This implementation of |mcount|
  49  * will grab the return address from the stack, and write it to stdout
  50  * as a binary stream, creating a gross execution trace the
  51  * instrumented program.
  52  *
  53  * For more info on gcc inline assembly, see:
  54  *
  55  *   <http://www.ibm.com/developerworks/linux/library/l-ia.html?dwzone=linux>
  56  *
  57  */
  58 void
  59 mcount()
  60 {
  61     register unsigned int caller;
  62     unsigned int buf[1];
  63
  64     // Grab the return address.
  65     asm("movl 4(%%esp),%0"
  66         : "=r"(caller));
  67
  68     buf[0] = caller;
  69     write(STDOUT_FILENO, buf, sizeof buf[0]);
  70 }