michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: /*
michael@0: 
michael@0:   A library that can be LD_PRELOAD-ed to dump a function's address on
michael@0:   function entry.
michael@0: 
michael@0:  */
michael@0: 
michael@0: #include <unistd.h>
michael@0: 
michael@0: /**
michael@0:  * When compiled with `-pg' (or even just `-p'), gcc inserts a call to
michael@0:  * |mcount| in each function prologue. This implementation of |mcount|
michael@0:  * will grab the return address from the stack, and write it to stdout
michael@0:  * as a binary stream, creating a gross execution trace the
michael@0:  * instrumented program.
michael@0:  *
michael@0:  * For more info on gcc inline assembly, see:
michael@0:  *
michael@0:  *   <http://www.ibm.com/developerworks/linux/library/l-ia.html?dwzone=linux>
michael@0:  *
michael@0:  */
michael@0: void
michael@0: mcount()
michael@0: {
michael@0:     register unsigned int caller;
michael@0:     unsigned int buf[1];
michael@0: 
michael@0:     // Grab the return address. 
michael@0:     asm("movl 4(%%esp),%0"
michael@0:         : "=r"(caller));
michael@0: 
michael@0:     buf[0] = caller;
michael@0:     write(STDOUT_FILENO, buf, sizeof buf[0]);
michael@0: }