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Use ptrace(2) LWP events to track threads reliably in truss.

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- truss can now log the system call invoked by a thread during a
  voluntary process exit.  No return value is logged, but the value passed
  to exit() is included in the trace output.  Arguments passed to thread
  exit system calls such as thr_exit() are not logged as voluntary thread
  exits cannot be distinguished from involuntary thread exits during a
  system call.
- New events are now reported for thread births and exits similar to the
  recently added events for new child processes when following forks.

Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D5561
This commit is contained in:
John Baldwin 2016-03-09 18:45:41 +00:00
parent 6fc8053f1a
commit b9befd33b4
3 changed files with 163 additions and 54 deletions
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203
usr.bin/truss/setup.c
View File

@ -61,7 +61,9 @@ SET_DECLARE(procabi, struct procabi);
static sig_atomic_t detaching;
static void new_proc(struct trussinfo *, pid_t);
static void enter_syscall(struct trussinfo *, struct threadinfo *,
struct ptrace_lwpinfo *);
static void new_proc(struct trussinfo *, pid_t, lwpid_t);
/*
* setup_and_wait() is called to start a process. All it really does
@ -87,7 +89,7 @@ setup_and_wait(struct trussinfo *info, char *command[])
if (waitpid(pid, NULL, 0) < 0)
err(1, "unexpect stop in waitpid");
new_proc(info, pid);
new_proc(info, pid, 0);
}
/*
@ -109,7 +111,7 @@ start_tracing(struct trussinfo *info, pid_t pid)
if (waitpid(pid, NULL, 0) < 0)
err(1, "Unexpect stop in waitpid");
new_proc(info, pid);
new_proc(info, pid, 0);
}
/*
@ -170,14 +172,71 @@ find_abi(pid_t 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
new_proc(struct trussinfo *info, pid_t pid)
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)
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 are attached to.
* this will kill any processes truss is attached to.
*/
LIST_FOREACH(np, &info->proclist, entries) {
if (np->pid == pid)
@ -187,11 +246,18 @@ new_proc(struct trussinfo *info, pid_t 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);
SLIST_INIT(&np->threadlist);
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
@ -199,7 +265,7 @@ free_proc(struct procinfo *p)
{
struct threadinfo *t, *t2;
SLIST_FOREACH_SAFE(t, &p->threadlist, entries, t2) {
LIST_FOREACH_SAFE(t, &p->threadlist, entries, t2) {
free(t);
}
LIST_REMOVE(p, entries);
@ -232,7 +298,6 @@ find_proc(struct trussinfo *info, pid_t pid)
/*
* Change curthread member based on (pid, lwpid).
* If it is a new thread, create a threadinfo structure.
*/
static void
find_thread(struct trussinfo *info, pid_t pid, lwpid_t lwpid)
@ -243,55 +308,30 @@ find_thread(struct trussinfo *info, pid_t pid, lwpid_t lwpid)
np = find_proc(info, pid);
assert(np != NULL);
SLIST_FOREACH(nt, &np->threadlist, entries) {
LIST_FOREACH(nt, &np->threadlist, entries) {
if (nt->tid == lwpid) {
info->curthread = nt;
return;
}
}
nt = calloc(1, sizeof(struct threadinfo));
if (nt == NULL)
err(1, "calloc() failed");
nt->proc = np;
nt->tid = lwpid;
SLIST_INSERT_HEAD(&np->threadlist, nt, entries);
info->curthread = nt;
errx(1, "could not find thread");
}
/*
* When a process exits, it no longer has any threads left. However,
* the main loop expects a valid curthread. In cases when a thread
* triggers the termination (e.g. calling exit or triggering a fault)
* we would ideally use that thread. However, if a process is killed
* by a signal sent from another process then there is no "correct"
* thread. We just punt and use the first 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 *np;
struct threadinfo *nt;
struct procinfo *p;
np = find_proc(info, pid);
assert(np != NULL);
p = find_proc(info, pid);
assert(p != NULL);
if (SLIST_EMPTY(&np->threadlist)) {
/*
* If an existing process exits right after we attach
* to it but before it posts any events, there won't
* be any threads. Create a dummy thread and set its
* "before" time to the global start time.
*/
nt = calloc(1, sizeof(struct threadinfo));
if (nt == NULL)
err(1, "calloc() failed");
nt->proc = np;
nt->tid = 0;
SLIST_INSERT_HEAD(&np->threadlist, nt, entries);
nt->before = info->start_time;
}
info->curthread = SLIST_FIRST(&np->threadlist);
info->curthread = LIST_FIRST(&p->threadlist);
assert(info->curthread != NULL);
assert(LIST_NEXT(info->curthread, entries) == NULL);
}
static void
@ -322,13 +362,12 @@ free_syscall(struct threadinfo *t)
}
static void
enter_syscall(struct trussinfo *info, struct ptrace_lwpinfo *pl)
enter_syscall(struct trussinfo *info, struct threadinfo *t,
struct ptrace_lwpinfo *pl)
{
struct threadinfo *t;
struct syscall *sc;
u_int i, narg;
t = info->curthread;
alloc_syscall(t, pl);
narg = MIN(pl->pl_syscall_narg, nitems(t->cs.args));
if (narg != 0 && t->proc->abi->fetch_args(info, narg) != 0) {
@ -377,6 +416,28 @@ enter_syscall(struct trussinfo *info, struct ptrace_lwpinfo *pl)
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)
{
@ -430,6 +491,7 @@ exit_syscall(struct trussinfo *info, struct ptrace_lwpinfo *pl)
* 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)
@ -471,6 +533,29 @@ print_line_prefix(struct trussinfo *info)
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)
{
@ -544,8 +629,11 @@ eventloop(struct trussinfo *info)
case CLD_KILLED:
case CLD_DUMPED:
find_exit_thread(info, si.si_pid);
if ((info->flags & COUNTONLY) == 0)
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;
@ -555,16 +643,27 @@ eventloop(struct trussinfo *info)
err(1, "ptrace(PT_LWPINFO)");
if (pl.pl_flags & PL_FLAG_CHILD) {
new_proc(info, si.si_pid);
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_SCE|PL_FLAG_SCX)) != 0) {
if (pl.pl_flags & PL_FLAG_SCE)
enter_syscall(info, &pl);
(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;

10
usr.bin/truss/syscalls.c
View File

@ -2054,6 +2054,16 @@ print_syscall_ret(struct trussinfo *trussinfo, int errorp, long *retval)
print_syscall(trussinfo);
fflush(trussinfo->outfile);
if (retval == NULL) {
/*
* This system call resulted in the current thread's exit,
* so there is no return value or error to display.
*/
fprintf(trussinfo->outfile, "\n");
return;
}
if (errorp) {
error = sysdecode_abi_to_freebsd_errno(t->proc->abi->abi,
retval[0]);

4
usr.bin/truss/truss.h
View File

@ -73,7 +73,7 @@ struct current_syscall {
struct threadinfo
{
SLIST_ENTRY(threadinfo) entries;
LIST_ENTRY(threadinfo) entries;
struct procinfo *proc;
lwpid_t tid;
int in_syscall;
@ -87,7 +87,7 @@ struct procinfo {
pid_t pid;
struct procabi *abi;
SLIST_HEAD(, threadinfo) threadlist;
LIST_HEAD(, threadinfo) threadlist;
};
struct trussinfo