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Introduce ltrace(1). This tool works with ld.so to inject utrace record for
each plt call, allowing to trace a binary linked against shared library at the
public function call level.

To do so, ltrace(1) sets up some environment variables to enable plt tracing
in ld.so, and invokes ktrace(2) for utrace events. ld.so will force lazy
binding and will send an utrace record in the plt resolver, without updating
the plt.

Minimal filtering capabilities are provided, inspired by Solaris' truss -u,
to limit tracing to libraries and/or symbol names. Non-traced libraries and
symbols will have the regular resolver processing, with the expected plt
update.

"Get it in" deraadt

/*	$OpenBSD: ktrace.c,v 1.25 2013/06/01 09:57:58 miod Exp $	*/
/*	$NetBSD: ktrace.c,v 1.4 1995/08/31 23:01:44 jtc Exp $	*/

/*-
 * Copyright (c) 1988, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/param.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/uio.h>
#include <sys/ktrace.h>

#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#include "ktrace.h"
#include "extern.h"

extern char *__progname;

static int rpid(const char *);
static void no_ktrace(int);
static void usage(void);

int	is_ltrace;

int
main(int argc, char *argv[])
{
	enum { NOTSET, CLEAR, CLEARALL } clear;
	int append, ch, fd, inherit, ops, pidset, trpoints;
	pid_t pid;
	char *tracefile, *tracespec;
	mode_t omask;
	struct stat sb;

	is_ltrace = strcmp(__progname, "ltrace") == 0;

	clear = NOTSET;
	append = ops = pidset = inherit = pid = 0;
	trpoints = is_ltrace ? KTRFAC_USER : DEF_POINTS;
	tracefile = DEF_TRACEFILE;
	tracespec = NULL;

	if (is_ltrace) {
		while ((ch = getopt(argc, argv, "af:iu:")) != -1)
			switch ((char)ch) {
			case 'a':
				append = 1;
				break;
			case 'f':
				tracefile = optarg;
				break;
			case 'i':
				inherit = 1;
				break;
			case 'u':
				tracespec = optarg;
				break;
			default:
				usage();
			}
	} else {
		while ((ch = getopt(argc, argv, "aBCcdf:g:ip:t:")) != -1)
			switch ((char)ch) {
			case 'a':
				append = 1;
				break;
			case 'B':
				putenv("LD_BIND_NOW=");
				break;
			case 'C':
				clear = CLEARALL;
				pidset = 1;
				break;
			case 'c':
				clear = CLEAR;
				break;
			case 'd':
				ops |= KTRFLAG_DESCEND;
				break;
			case 'f':
				tracefile = optarg;
				break;
			case 'g':
				pid = -rpid(optarg);
				pidset = 1;
				break;
			case 'i':
				inherit = 1;
				break;
			case 'p':
				pid = rpid(optarg);
				pidset = 1;
				break;
			case 't':
				trpoints = getpoints(optarg);
				if (trpoints < 0) {
					warnx("unknown facility in %s", optarg);
					usage();
				}
				break;
			default:
				usage();
			}
	}

	argv += optind;
	argc -= optind;
	
	if ((pidset && *argv) || (!pidset && !*argv && clear != CLEAR))
		usage();

	if (inherit)
		trpoints |= KTRFAC_INHERIT;

	(void)signal(SIGSYS, no_ktrace);
	if (clear != NOTSET) {
		if (clear == CLEARALL) {
			ops = KTROP_CLEAR | KTRFLAG_DESCEND;
			trpoints = ALL_POINTS;
			pid = 1;
		} else
			ops |= pid ? KTROP_CLEAR : KTROP_CLEARFILE;

		if (ktrace(tracefile, ops, trpoints, pid) < 0)
			err(1, "%s", tracefile);
		exit(0);
	}

	omask = umask(S_IRWXG|S_IRWXO);
	if (append) {
		if ((fd = open(tracefile, O_CREAT | O_WRONLY, DEFFILEMODE)) < 0)
			err(1, "%s", tracefile);
		if (fstat(fd, &sb) != 0 || sb.st_uid != getuid())
			errx(1, "Refuse to append to %s: not owned by you.",
			    tracefile);
	} else {
		if (unlink(tracefile) == -1 && errno != ENOENT)
			err(1, "unlink %s", tracefile);
		if ((fd = open(tracefile, O_CREAT | O_EXCL | O_WRONLY,
		    DEFFILEMODE)) < 0)
			err(1, "%s", tracefile);
	}
	(void)umask(omask);
	(void)close(fd);

	if (*argv) { 
		if (is_ltrace) {
			if (setenv("LD_TRACE_PLT", inherit ? "i" : "", 1) < 0)
				err(1, "setenv(LD_TRACE_PLT)");
			if (tracespec &&
			    setenv("LD_TRACE_PLTSPEC", tracespec, 1) < 0)
				err(1, "setenv(LD_TRACE_PLTSPEC)");
		}
		if (ktrace(tracefile, ops, trpoints, getpid()) < 0)
			err(1, "%s", tracefile);
		execvp(argv[0], &argv[0]);
		err(1, "exec of '%s' failed", argv[0]);
	}
	else if (ktrace(tracefile, ops, trpoints, pid) < 0)
		err(1, "%s", tracefile);
	exit(0);
}

static int
rpid(const char *p)
{
	static int first;

	if (first++) {
		warnx("only one -g or -p flag is permitted.");
		usage();
	}
	if (!*p) {
		warnx("illegal process id.");
		usage();
	}
	return(atoi(p));
}

static void
usage(void)
{
	if (is_ltrace)
		fprintf(stderr, "usage: %s [-ai] [-f trfile] [-u trspec]"
		    "  comand\n",
		    __progname);
	else
		fprintf(stderr, "usage: %s [-aBCcdi] [-f trfile] [-g pgid]"
		    " [-p pid] [-t trstr]\n"
		    "       %s [-adi] [-f trfile] [-t trstr] command\n",
		    __progname, __progname);
	exit(1);
}

/* ARGSUSED */
static void
no_ktrace(int signo)
{
	char buf[8192];

	snprintf(buf, sizeof(buf),
"error:\tktrace() system call not supported in the running kernel\n\tre-compile kernel with 'option KTRACE'\n");
	write(STDERR_FILENO, buf, strlen(buf));
	_exit(1);
}