gecko-dev/tools/reorder/mcount.c
2012-05-21 12:12:37 +01:00

39 lines
995 B
C

/* 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]);
}