xref: /freebsd/usr.bin/truss/setup.c (revision 3cbad8287aa0ed72e07df1130ce2ae490642e63a)

/*-
 * SPDX-License-Identifier: BSD-4-Clause
 *
 * Copyright 1997 Sean Eric Fagan
 *
 * 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by Sean Eric Fagan
 * 4. Neither the name of the author may be used to endorse or promote
 *    products derived from this software without specific prior written
 *    permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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/cdefs.h>
__FBSDID("$FreeBSD$");

/*
 * Various setup functions for truss.  Not the cleanest-written code,
 * I'm afraid.
 */

#include <sys/ptrace.h>
#include <sys/sysctl.h>
#include <sys/time.h>
#include <sys/wait.h>

#include <assert.h>
#include <err.h>
#include <errno.h>
#include <signal.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sysdecode.h>
#include <time.h>
#include <unistd.h>

#include "truss.h"
#include "syscall.h"
#include "extern.h"

struct procabi_table {
	const char *name;
	struct procabi *abi;
};

static sig_atomic_t detaching;

static void	enter_syscall(struct trussinfo *, struct threadinfo *,
		    struct ptrace_lwpinfo *);
static void	new_proc(struct trussinfo *, pid_t, lwpid_t);


static struct procabi cloudabi32 = {
	.type = "CloudABI32",
	.abi = SYSDECODE_ABI_CLOUDABI32,
	.pointer_size = sizeof(uint32_t),
	.extra_syscalls = STAILQ_HEAD_INITIALIZER(cloudabi32.extra_syscalls),
	.syscalls = { NULL }
};

static struct procabi cloudabi64 = {
	.type = "CloudABI64",
	.abi = SYSDECODE_ABI_CLOUDABI64,
	.pointer_size = sizeof(uint64_t),
	.extra_syscalls = STAILQ_HEAD_INITIALIZER(cloudabi64.extra_syscalls),
	.syscalls = { NULL }
};

static struct procabi freebsd = {
	.type = "FreeBSD",
	.abi = SYSDECODE_ABI_FREEBSD,
	.pointer_size = sizeof(void *),
	.extra_syscalls = STAILQ_HEAD_INITIALIZER(freebsd.extra_syscalls),
	.syscalls = { NULL }
};

#if !defined(__SIZEOF_POINTER__)
#error "Use a modern compiler."
#endif

#if __SIZEOF_POINTER__ > 4
static struct procabi freebsd32 = {
	.type = "FreeBSD32",
	.abi = SYSDECODE_ABI_FREEBSD32,
	.pointer_size = sizeof(uint32_t),
	.compat_prefix = "freebsd32_",
	.extra_syscalls = STAILQ_HEAD_INITIALIZER(freebsd32.extra_syscalls),
	.syscalls = { NULL }
};
#endif

static struct procabi linux = {
	.type = "Linux",
	.abi = SYSDECODE_ABI_LINUX,
	.pointer_size = sizeof(void *),
	.extra_syscalls = STAILQ_HEAD_INITIALIZER(linux.extra_syscalls),
	.syscalls = { NULL }
};

#if __SIZEOF_POINTER__ > 4
static struct procabi linux32 = {
	.type = "Linux32",
	.abi = SYSDECODE_ABI_LINUX32,
	.pointer_size = sizeof(uint32_t),
	.extra_syscalls = STAILQ_HEAD_INITIALIZER(linux32.extra_syscalls),
	.syscalls = { NULL }
};
#endif

static struct procabi_table abis[] = {
	{ "CloudABI ELF32", &cloudabi32 },
	{ "CloudABI ELF64", &cloudabi64 },
#if __SIZEOF_POINTER__ == 4
	{ "FreeBSD ELF32", &freebsd },
#elif __SIZEOF_POINTER__ == 8
	{ "FreeBSD ELF64", &freebsd },
	{ "FreeBSD ELF32", &freebsd32 },
#else
#error "Unsupported pointer size"
#endif
#if defined(__powerpc64__)
	{ "FreeBSD ELF64 V2", &freebsd },
#endif
#if defined(__amd64__)
	{ "FreeBSD a.out", &freebsd32 },
#endif
#if defined(__i386__)
	{ "FreeBSD a.out", &freebsd },
#endif
#if __SIZEOF_POINTER__ >= 8
	{ "Linux ELF64", &linux },
	{ "Linux ELF32", &linux32 },
#else
	{ "Linux ELF32", &linux },
#endif
};

/*
 * setup_and_wait() is called to start a process.  All it really does
 * is fork(), enable tracing in the child, and then exec the given
 * command.  At that point, the child process stops, and the parent
 * can wake up and deal with it.
 */
void
setup_and_wait(struct trussinfo *info, char *command[])
{
	pid_t pid;

	pid = vfork();
	if (pid == -1)
		err(1, "fork failed");
	if (pid == 0) {	/* Child */
		ptrace(PT_TRACE_ME, 0, 0, 0);
		execvp(command[0], command);
		err(1, "execvp %s", command[0]);
	}

	/* Only in the parent here */
	if (waitpid(pid, NULL, 0) < 0)
		err(1, "unexpect stop in waitpid");

	new_proc(info, pid, 0);
}

/*
 * start_tracing is called to attach to an existing process.
 */
void
start_tracing(struct trussinfo *info, pid_t pid)
{
	int ret, retry;

	retry = 10;
	do {
		ret = ptrace(PT_ATTACH, pid, NULL, 0);
		usleep(200);
	} while (ret && retry-- > 0);
	if (ret)
		err(1, "can not attach to target process");

	if (waitpid(pid, NULL, 0) < 0)
		err(1, "Unexpect stop in waitpid");

	new_proc(info, pid, 0);
}

/*
 * Restore a process back to it's pre-truss state.
 * Called for SIGINT, SIGTERM, SIGQUIT.  This only
 * applies if truss was told to monitor an already-existing
 * process.
 */
void
restore_proc(int signo __unused)
{

	detaching = 1;
}

static void
detach_proc(pid_t pid)
{

	/* stop the child so that we can detach */
	kill(pid, SIGSTOP);
	if (waitpid(pid, NULL, 0) < 0)
		err(1, "Unexpected stop in waitpid");

	if (ptrace(PT_DETACH, pid, (caddr_t)1, 0) < 0)
		err(1, "Can not detach the process");

	kill(pid, SIGCONT);
}

/*
 * Determine the ABI.  This is called after every exec, and when
 * a process is first monitored.
 */
static struct procabi *
find_abi(pid_t pid)
{
	size_t len;
	unsigned int i;
	int error;
	int mib[4];
	char progt[32];

	len = sizeof(progt);
	mib[0] = CTL_KERN;
	mib[1] = KERN_PROC;
	mib[2] = KERN_PROC_SV_NAME;
	mib[3] = pid;
	error = sysctl(mib, 4, progt, &len, NULL, 0);
	if (error != 0)
		err(2, "can not get sysvec name");

	for (i = 0; i < nitems(abis); i++) {
		if (strcmp(abis[i].name, progt) == 0)
			return (abis[i].abi);
	}
	warnx("ABI %s for pid %ld is not supported", progt, (long)pid);
	return (NULL);
}

static struct threadinfo *
new_thread(struct procinfo *p, lwpid_t lwpid)
{
	struct threadinfo *nt;

	/*
	 * If this happens it means there is a bug in truss.  Unfortunately
	 * this will kill any processes truss is attached to.
	 */
	LIST_FOREACH(nt, &p->threadlist, entries) {
		if (nt->tid == lwpid)
			errx(1, "Duplicate thread for LWP %ld", (long)lwpid);
	}

	nt = calloc(1, sizeof(struct threadinfo));
	if (nt == NULL)
		err(1, "calloc() failed");
	nt->proc = p;
	nt->tid = lwpid;
	LIST_INSERT_HEAD(&p->threadlist, nt, entries);
	return (nt);
}

static void
free_thread(struct threadinfo *t)
{

	LIST_REMOVE(t, entries);
	free(t);
}

static void
add_threads(struct trussinfo *info, struct procinfo *p)
{
	struct ptrace_lwpinfo pl;
	struct threadinfo *t;
	lwpid_t *lwps;
	int i, nlwps;

	nlwps = ptrace(PT_GETNUMLWPS, p->pid, NULL, 0);
	if (nlwps == -1)
		err(1, "Unable to fetch number of LWPs");
	assert(nlwps > 0);
	lwps = calloc(nlwps, sizeof(*lwps));
	nlwps = ptrace(PT_GETLWPLIST, p->pid, (caddr_t)lwps, nlwps);
	if (nlwps == -1)
		err(1, "Unable to fetch LWP list");
	for (i = 0; i < nlwps; i++) {
		t = new_thread(p, lwps[i]);
		if (ptrace(PT_LWPINFO, lwps[i], (caddr_t)&pl, sizeof(pl)) == -1)
			err(1, "ptrace(PT_LWPINFO)");
		if (pl.pl_flags & PL_FLAG_SCE) {
			info->curthread = t;
			enter_syscall(info, t, &pl);
		}
	}
	free(lwps);
}

static void
new_proc(struct trussinfo *info, pid_t pid, lwpid_t lwpid)
{
	struct procinfo *np;

	/*
	 * If this happens it means there is a bug in truss.  Unfortunately
	 * this will kill any processes truss is attached to.
	 */
	LIST_FOREACH(np, &info->proclist, entries) {
		if (np->pid == pid)
			errx(1, "Duplicate process for pid %ld", (long)pid);
	}

	if (info->flags & FOLLOWFORKS)
		if (ptrace(PT_FOLLOW_FORK, pid, NULL, 1) == -1)
			err(1, "Unable to follow forks for pid %ld", (long)pid);
	if (ptrace(PT_LWP_EVENTS, pid, NULL, 1) == -1)
		err(1, "Unable to enable LWP events for pid %ld", (long)pid);
	np = calloc(1, sizeof(struct procinfo));
	np->pid = pid;
	np->abi = find_abi(pid);
	LIST_INIT(&np->threadlist);
	LIST_INSERT_HEAD(&info->proclist, np, entries);

	if (lwpid != 0)
		new_thread(np, lwpid);
	else
		add_threads(info, np);
}

static void
free_proc(struct procinfo *p)
{
	struct threadinfo *t, *t2;

	LIST_FOREACH_SAFE(t, &p->threadlist, entries, t2) {
		free(t);
	}
	LIST_REMOVE(p, entries);
	free(p);
}

static void
detach_all_procs(struct trussinfo *info)
{
	struct procinfo *p, *p2;

	LIST_FOREACH_SAFE(p, &info->proclist, entries, p2) {
		detach_proc(p->pid);
		free_proc(p);
	}
}

static struct procinfo *
find_proc(struct trussinfo *info, pid_t pid)
{
	struct procinfo *np;

	LIST_FOREACH(np, &info->proclist, entries) {
		if (np->pid == pid)
			return (np);
	}

	return (NULL);
}

/*
 * Change curthread member based on (pid, lwpid).
 */
static void
find_thread(struct trussinfo *info, pid_t pid, lwpid_t lwpid)
{
	struct procinfo *np;
	struct threadinfo *nt;

	np = find_proc(info, pid);
	assert(np != NULL);

	LIST_FOREACH(nt, &np->threadlist, entries) {
		if (nt->tid == lwpid) {
			info->curthread = nt;
			return;
		}
	}
	errx(1, "could not find thread");
}

/*
 * When a process exits, it should have exactly one thread left.
 * All of the other threads should have reported thread exit events.
 */
static void
find_exit_thread(struct trussinfo *info, pid_t pid)
{
	struct procinfo *p;

	p = find_proc(info, pid);
	assert(p != NULL);

	info->curthread = LIST_FIRST(&p->threadlist);
	assert(info->curthread != NULL);
	assert(LIST_NEXT(info->curthread, entries) == NULL);
}

static void
alloc_syscall(struct threadinfo *t, struct ptrace_lwpinfo *pl)
{
	u_int i;

	assert(t->in_syscall == 0);
	assert(t->cs.number == 0);
	assert(t->cs.sc == NULL);
	assert(t->cs.nargs == 0);
	for (i = 0; i < nitems(t->cs.s_args); i++)
		assert(t->cs.s_args[i] == NULL);
	memset(t->cs.args, 0, sizeof(t->cs.args));
	t->cs.number = pl->pl_syscall_code;
	t->in_syscall = 1;
}

static void
free_syscall(struct threadinfo *t)
{
	u_int i;

	for (i = 0; i < t->cs.nargs; i++)
		free(t->cs.s_args[i]);
	memset(&t->cs, 0, sizeof(t->cs));
	t->in_syscall = 0;
}

static void
enter_syscall(struct trussinfo *info, struct threadinfo *t,
    struct ptrace_lwpinfo *pl)
{
	struct syscall *sc;
	u_int i, narg;

	alloc_syscall(t, pl);
	narg = MIN(pl->pl_syscall_narg, nitems(t->cs.args));
	if (narg != 0 && ptrace(PT_GET_SC_ARGS, t->tid, (caddr_t)t->cs.args,
	    sizeof(t->cs.args)) != 0) {
		free_syscall(t);
		return;
	}

	sc = get_syscall(t, t->cs.number, narg);
	if (sc->unknown)
		fprintf(info->outfile, "-- UNKNOWN %s SYSCALL %d --\n",
		    t->proc->abi->type, t->cs.number);

	t->cs.nargs = sc->decode.nargs;
	assert(sc->decode.nargs <= nitems(t->cs.s_args));

	t->cs.sc = sc;

	/*
	 * At this point, we set up the system call arguments.
	 * We ignore any OUT ones, however -- those are arguments that
	 * are set by the system call, and so are probably meaningless
	 * now.	This doesn't currently support arguments that are
	 * passed in *and* out, however.
	 */
#if DEBUG
	fprintf(stderr, "syscall %s(", sc->name);
#endif
	for (i = 0; i < t->cs.nargs; i++) {
#if DEBUG
		fprintf(stderr, "0x%lx%s",
		    t->cs.args[sc->decode.args[i].offset],
		    i < (t->cs.nargs - 1) ? "," : "");
#endif
		if (!(sc->decode.args[i].type & OUT)) {
			t->cs.s_args[i] = print_arg(&sc->decode.args[i],
			    t->cs.args, NULL, info);
		}
	}
#if DEBUG
	fprintf(stderr, ")\n");
#endif

	clock_gettime(CLOCK_REALTIME, &t->before);
}

/*
 * When a thread exits voluntarily (including when a thread calls
 * exit() to trigger a process exit), the thread's internal state
 * holds the arguments passed to the exit system call.  When the
 * thread's exit is reported, log that system call without a return
 * value.
 */
static void
thread_exit_syscall(struct trussinfo *info)
{
	struct threadinfo *t;

	t = info->curthread;
	if (!t->in_syscall)
		return;

	clock_gettime(CLOCK_REALTIME, &t->after);

	print_syscall_ret(info, 0, NULL);
	free_syscall(t);
}

static void
exit_syscall(struct trussinfo *info, struct ptrace_lwpinfo *pl)
{
	struct threadinfo *t;
	struct procinfo *p;
	struct syscall *sc;
	struct ptrace_sc_ret psr;
	u_int i;

	t = info->curthread;
	if (!t->in_syscall)
		return;

	clock_gettime(CLOCK_REALTIME, &t->after);
	p = t->proc;
	if (ptrace(PT_GET_SC_RET, t->tid, (caddr_t)&psr, sizeof(psr)) != 0) {
		free_syscall(t);
		return;
	}

	sc = t->cs.sc;
	/*
	 * Here, we only look for arguments that have OUT masked in --
	 * otherwise, they were handled in enter_syscall().
	 */
	for (i = 0; i < sc->decode.nargs; i++) {
		char *temp;

		if (sc->decode.args[i].type & OUT) {
			/*
			 * If an error occurred, then don't bother
			 * getting the data; it may not be valid.
			 */
			if (psr.sr_error != 0) {
				asprintf(&temp, "0x%lx",
				    t->cs.args[sc->decode.args[i].offset]);
			} else {
				temp = print_arg(&sc->decode.args[i],
				    t->cs.args, psr.sr_retval, info);
			}
			t->cs.s_args[i] = temp;
		}
	}

	print_syscall_ret(info, psr.sr_error, psr.sr_retval);
	free_syscall(t);

	/*
	 * If the process executed a new image, check the ABI.  If the
	 * new ABI isn't supported, stop tracing this process.
	 */
	if (pl->pl_flags & PL_FLAG_EXEC) {
		assert(LIST_NEXT(LIST_FIRST(&p->threadlist), entries) == NULL);
		p->abi = find_abi(p->pid);
		if (p->abi == NULL) {
			if (ptrace(PT_DETACH, p->pid, (caddr_t)1, 0) < 0)
				err(1, "Can not detach the process");
			free_proc(p);
		}
	}
}

int
print_line_prefix(struct trussinfo *info)
{
	struct timespec timediff;
	struct threadinfo *t;
	int len;

	len = 0;
	t = info->curthread;
	if (info->flags & (FOLLOWFORKS | DISPLAYTIDS)) {
		if (info->flags & FOLLOWFORKS)
			len += fprintf(info->outfile, "%5d", t->proc->pid);
		if ((info->flags & (FOLLOWFORKS | DISPLAYTIDS)) ==
		    (FOLLOWFORKS | DISPLAYTIDS))
			len += fprintf(info->outfile, " ");
		if (info->flags & DISPLAYTIDS)
			len += fprintf(info->outfile, "%6d", t->tid);
		len += fprintf(info->outfile, ": ");
	}
	if (info->flags & ABSOLUTETIMESTAMPS) {
		timespecsub(&t->after, &info->start_time, &timediff);
		len += fprintf(info->outfile, "%jd.%09ld ",
		    (intmax_t)timediff.tv_sec, timediff.tv_nsec);
	}
	if (info->flags & RELATIVETIMESTAMPS) {
		timespecsub(&t->after, &t->before, &timediff);
		len += fprintf(info->outfile, "%jd.%09ld ",
		    (intmax_t)timediff.tv_sec, timediff.tv_nsec);
	}
	return (len);
}

static void
report_thread_death(struct trussinfo *info)
{
	struct threadinfo *t;

	t = info->curthread;
	clock_gettime(CLOCK_REALTIME, &t->after);
	print_line_prefix(info);
	fprintf(info->outfile, "<thread %ld exited>\n", (long)t->tid);
}

static void
report_thread_birth(struct trussinfo *info)
{
	struct threadinfo *t;

	t = info->curthread;
	clock_gettime(CLOCK_REALTIME, &t->after);
	t->before = t->after;
	print_line_prefix(info);
	fprintf(info->outfile, "<new thread %ld>\n", (long)t->tid);
}

static void
report_exit(struct trussinfo *info, siginfo_t *si)
{
	struct threadinfo *t;

	t = info->curthread;
	clock_gettime(CLOCK_REALTIME, &t->after);
	print_line_prefix(info);
	if (si->si_code == CLD_EXITED)
		fprintf(info->outfile, "process exit, rval = %u\n",
		    si->si_status);
	else
		fprintf(info->outfile, "process killed, signal = %u%s\n",
		    si->si_status, si->si_code == CLD_DUMPED ?
		    " (core dumped)" : "");
}

static void
report_new_child(struct trussinfo *info)
{
	struct threadinfo *t;

	t = info->curthread;
	clock_gettime(CLOCK_REALTIME, &t->after);
	t->before = t->after;
	print_line_prefix(info);
	fprintf(info->outfile, "<new process>\n");
}

void
decode_siginfo(FILE *fp, siginfo_t *si)
{
	const char *str;

	fprintf(fp, " code=");
	str = sysdecode_sigcode(si->si_signo, si->si_code);
	if (str == NULL)
		fprintf(fp, "%d", si->si_code);
	else
		fprintf(fp, "%s", str);
	switch (si->si_code) {
	case SI_NOINFO:
		break;
	case SI_QUEUE:
		fprintf(fp, " value=%p", si->si_value.sival_ptr);
		/* FALLTHROUGH */
	case SI_USER:
	case SI_LWP:
		fprintf(fp, " pid=%jd uid=%jd", (intmax_t)si->si_pid,
		    (intmax_t)si->si_uid);
		break;
	case SI_TIMER:
		fprintf(fp, " value=%p", si->si_value.sival_ptr);
		fprintf(fp, " timerid=%d", si->si_timerid);
		fprintf(fp, " overrun=%d", si->si_overrun);
		if (si->si_errno != 0)
			fprintf(fp, " errno=%d", si->si_errno);
		break;
	case SI_ASYNCIO:
		fprintf(fp, " value=%p", si->si_value.sival_ptr);
		break;
	case SI_MESGQ:
		fprintf(fp, " value=%p", si->si_value.sival_ptr);
		fprintf(fp, " mqd=%d", si->si_mqd);
		break;
	default:
		switch (si->si_signo) {
		case SIGILL:
		case SIGFPE:
		case SIGSEGV:
		case SIGBUS:
			fprintf(fp, " trapno=%d", si->si_trapno);
			fprintf(fp, " addr=%p", si->si_addr);
			break;
		case SIGCHLD:
			fprintf(fp, " pid=%jd uid=%jd", (intmax_t)si->si_pid,
			    (intmax_t)si->si_uid);
			fprintf(fp, " status=%d", si->si_status);
			break;
		}
	}
}

static void
report_signal(struct trussinfo *info, siginfo_t *si, struct ptrace_lwpinfo *pl)
{
	struct threadinfo *t;
	const char *signame;

	t = info->curthread;
	clock_gettime(CLOCK_REALTIME, &t->after);
	print_line_prefix(info);
	signame = sysdecode_signal(si->si_status);
	if (signame == NULL)
		signame = "?";
	fprintf(info->outfile, "SIGNAL %u (%s)", si->si_status, signame);
	if (pl->pl_event == PL_EVENT_SIGNAL && pl->pl_flags & PL_FLAG_SI)
		decode_siginfo(info->outfile, &pl->pl_siginfo);
	fprintf(info->outfile, "\n");

}

/*
 * Wait for events until all the processes have exited or truss has been
 * asked to stop.
 */
void
eventloop(struct trussinfo *info)
{
	struct ptrace_lwpinfo pl;
	siginfo_t si;
	int pending_signal;

	while (!LIST_EMPTY(&info->proclist)) {
		if (detaching) {
			detach_all_procs(info);
			return;
		}

		if (waitid(P_ALL, 0, &si, WTRAPPED | WEXITED) == -1) {
			if (errno == EINTR)
				continue;
			err(1, "Unexpected error from waitid");
		}

		assert(si.si_signo == SIGCHLD);

		switch (si.si_code) {
		case CLD_EXITED:
		case CLD_KILLED:
		case CLD_DUMPED:
			find_exit_thread(info, si.si_pid);
			if ((info->flags & COUNTONLY) == 0) {
				if (si.si_code == CLD_EXITED)
					thread_exit_syscall(info);
				report_exit(info, &si);
			}
			free_proc(info->curthread->proc);
			info->curthread = NULL;
			break;
		case CLD_TRAPPED:
			if (ptrace(PT_LWPINFO, si.si_pid, (caddr_t)&pl,
			    sizeof(pl)) == -1)
				err(1, "ptrace(PT_LWPINFO)");

			if (pl.pl_flags & PL_FLAG_CHILD) {
				new_proc(info, si.si_pid, pl.pl_lwpid);
				assert(LIST_FIRST(&info->proclist)->abi !=
				    NULL);
			} else if (pl.pl_flags & PL_FLAG_BORN)
				new_thread(find_proc(info, si.si_pid),
				    pl.pl_lwpid);
			find_thread(info, si.si_pid, pl.pl_lwpid);

			if (si.si_status == SIGTRAP &&
			    (pl.pl_flags & (PL_FLAG_BORN|PL_FLAG_EXITED|
			    PL_FLAG_SCE|PL_FLAG_SCX)) != 0) {
				if (pl.pl_flags & PL_FLAG_BORN) {
					if ((info->flags & COUNTONLY) == 0)
						report_thread_birth(info);
				} else if (pl.pl_flags & PL_FLAG_EXITED) {
					if ((info->flags & COUNTONLY) == 0)
						report_thread_death(info);
					free_thread(info->curthread);
					info->curthread = NULL;
				} else if (pl.pl_flags & PL_FLAG_SCE)
					enter_syscall(info, info->curthread, &pl);
				else if (pl.pl_flags & PL_FLAG_SCX)
					exit_syscall(info, &pl);
				pending_signal = 0;
			} else if (pl.pl_flags & PL_FLAG_CHILD) {
				if ((info->flags & COUNTONLY) == 0)
					report_new_child(info);
				pending_signal = 0;
			} else {
				if ((info->flags & NOSIGS) == 0)
					report_signal(info, &si, &pl);
				pending_signal = si.si_status;
			}
			ptrace(PT_SYSCALL, si.si_pid, (caddr_t)1,
			    pending_signal);
			break;
		case CLD_STOPPED:
			errx(1, "waitid reported CLD_STOPPED");
		case CLD_CONTINUED:
			break;
		}
	}
}