/*
* Wait for a stopped process to be set running again by some other debugger.
* This is typically not required by /proc-based debuggers, since the usual
* model is that one debugger controls one victim. But DTrace, as usual, has
* its own needs: the stop() action assumes that prun(1) or some other tool
* will be applied to resume the victim process. This could be solved by
* adding a PCWRUN directive to /proc, but that seems like overkill unless
* other debuggers end up needing this functionality, so we implement a cheap
* equivalent to PCWRUN using the set of existing kernel mechanisms.
*
* Our intent is really not just to wait for the victim to run, but rather to
* wait for it to run and then stop again for a reason other than the current
* PR_REQUESTED stop. Since PCWSTOP/Pstopstatus() can be applied repeatedly
* to a stopped process and will return the same result without affecting the
* victim, we can just perform these operations repeatedly until Pstate()
* changes, the representative LWP ID changes, or the stop timestamp advances.
* dt_gproc_control() will then rediscover the new state and continue as usual.
* When the process is still stopped in the same exact state, we sleep for a
* brief interval before waiting again so as not to spin consuming CPU cycles.
*/
static void
dt_proc_waitrun(dt_proc_t *dpr)
{
struct ps_prochandle *P = dpr->dpr_proc;
const lwpstatus_t *psp = &Pstatus(P)->pr_lwp;
int krflag = psp->pr_flags & (PR_KLC | PR_RLC);
timestruc_t tstamp = psp->pr_tstamp;
lwpid_t lwpid = psp->pr_lwpid;
const long wstop = PCWSTOP;
int pfd = Pctlfd(P);
assert(DT_MUTEX_HELD(&dpr->dpr_lock));
assert(psp->pr_flags & PR_STOPPED);
assert(Pstate(P) == PS_STOP);
/*
* While we are waiting for the victim to run, clear PR_KLC and PR_RLC
* so that if the libdtrace client is killed, the victim stays stopped.
* dt_proc_destroy() will also observe this and perform PRELEASE_HANG.
*/
(void) Punsetflags(P, krflag);
Psync(P);
(void) pthread_mutex_unlock(&dpr->dpr_lock);
while (!dpr->dpr_quit) {
if (write(pfd, &wstop, sizeof (wstop)) == -1 && errno == EINTR)
continue; /* check dpr_quit and continue waiting */
(void) pthread_mutex_lock(&dpr->dpr_lock);
(void) Pstopstatus(P, PCNULL, 0);
psp = &Pstatus(P)->pr_lwp;
/*
* If we've reached a new state, found a new representative, or
* the stop timestamp has changed, restore PR_KLC/PR_RLC to its
* original setting and then return with dpr_lock held.
*/
if (Pstate(P) != PS_STOP || psp->pr_lwpid != lwpid ||
bcmp(&psp->pr_tstamp, &tstamp, sizeof (tstamp)) != 0) {
(void) Psetflags(P, krflag);
Psync(P);
return;
}
(void) pthread_mutex_unlock(&dpr->dpr_lock);
(void) poll(NULL, 0, MILLISEC / 2);
}
(void) pthread_mutex_lock(&dpr->dpr_lock);
}
/*
* Utility function to modify lwp registers. This is done using either the
* process control file or per-lwp control file as necessary.
*/
static int
setlwpregs(struct ps_prochandle *P, lwpid_t lwpid, long cmd,
const void *rp, size_t n)
{
iovec_t iov[2];
char fname[PATH_MAX];
int fd;
if (P->state != PS_STOP) {
errno = EBUSY;
return (-1);
}
iov[0].iov_base = (caddr_t)&cmd;
iov[0].iov_len = sizeof (long);
iov[1].iov_base = (caddr_t)rp;
iov[1].iov_len = n;
/*
* Writing the process control file writes the representative lwp.
* Psync before we write to make sure we are consistent with the
* primary interfaces. Similarly, make sure to update P->status
* afterward if we are modifying one of its register sets.
*/
if (P->status.pr_lwp.pr_lwpid == lwpid) {
Psync(P);
if (writev(P->ctlfd, iov, 2) == -1)
return (-1);
if (cmd == PCSREG)
(void) memcpy(P->status.pr_lwp.pr_reg, rp, n);
else if (cmd == PCSFPREG)
(void) memcpy(&P->status.pr_lwp.pr_fpreg, rp, n);
return (0);
}
/*
* If the lwp we want is not the representative lwp, we need to
* open the ctl file for that specific lwp.
*/
(void) snprintf(fname, sizeof (fname), "%s/%d/lwp/%d/lwpctl",
procfs_path, (int)P->status.pr_pid, (int)lwpid);
if ((fd = open(fname, O_WRONLY)) >= 0) {
if (writev(fd, iov, 2) > 0) {
(void) close(fd);
return (0);
}
(void) close(fd);
}
return (-1);
}
/*
* Main loop for all victim process control threads. We initialize all the
* appropriate /proc control mechanisms, and then enter a loop waiting for
* the process to stop on an event or die. We process any events by calling
* appropriate subroutines, and exit when the victim dies or we lose control.
*
* The control thread synchronizes the use of dpr_proc with other libdtrace
* threads using dpr_lock. We hold the lock for all of our operations except
* waiting while the process is running: this is accomplished by writing a
* PCWSTOP directive directly to the underlying /proc/<pid>/ctl file. If the
* libdtrace client wishes to exit or abort our wait, SIGCANCEL can be used.
*/
static void *
dt_proc_control(void *arg)
{
dt_proc_control_data_t *datap = arg;
dtrace_hdl_t *dtp = datap->dpcd_hdl;
dt_proc_t *dpr = datap->dpcd_proc;
dt_proc_hash_t *dph = dpr->dpr_hdl->dt_procs;
struct ps_prochandle *P = dpr->dpr_proc;
#if defined(sun)
int pfd = Pctlfd(P);
const long wstop = PCWSTOP;
#endif
int notify = B_FALSE;
/*
* We disable the POSIX thread cancellation mechanism so that the
* client program using libdtrace can't accidentally cancel our thread.
* dt_proc_destroy() uses SIGCANCEL explicitly to simply poke us out
* of PCWSTOP with EINTR, at which point we will see dpr_quit and exit.
*/
(void) pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, NULL);
dpr->dpr_pid = proc_getpid(P);
int pid = dpr->dpr_pid;
/*
* Set up the corresponding process for tracing by libdtrace. We want
* to be able to catch breakpoints and efficiently single-step over
* them, and we need to enable librtld_db to watch libdl activity.
*/
do_ptrace(__func__, PTRACE_ATTACH, dpr->dpr_pid, 0, 0);
(void) pthread_mutex_lock(&dpr->dpr_lock);
(void) Punsetflags(P, PR_ASYNC); /* require synchronous mode */
(void) Psetflags(P, PR_BPTADJ); /* always adjust eip on x86 */
(void) Punsetflags(P, PR_FORK); /* do not inherit on fork */
(void) Pfault(P, FLTBPT, B_TRUE); /* always trace breakpoints */
(void) Pfault(P, FLTTRACE, B_TRUE); /* always trace single-step */
/*
* We must trace exit from exec() system calls so that if the exec is
* successful, we can reset our breakpoints and re-initialize libproc.
*/
(void) Psysexit(P, SYS_exec, B_TRUE);
(void) Psysexit(P, SYS_execve, B_TRUE);
/*
* We must trace entry and exit for fork() system calls in order to
* disable our breakpoints temporarily during the fork. We do not set
* the PR_FORK flag, so if fork succeeds the child begins executing and
* does not inherit any other tracing behaviors or a control thread.
*/
(void) Psysentry(P, SYS_vfork, B_TRUE);
(void) Psysexit(P, SYS_vfork, B_TRUE);
(void) Psysentry(P, SYS_fork1, B_TRUE);
(void) Psysexit(P, SYS_fork1, B_TRUE);
(void) Psysentry(P, SYS_forkall, B_TRUE);
(void) Psysexit(P, SYS_forkall, B_TRUE);
(void) Psysentry(P, SYS_forksys, B_TRUE);
(void) Psysexit(P, SYS_forksys, B_TRUE);
Psync(P); /* enable all /proc changes */
dt_proc_attach(dpr, B_FALSE); /* enable rtld breakpoints */
/*
* If PR_KLC is set, we created the process; otherwise we grabbed it.
* Check for an appropriate stop request and wait for dt_proc_continue.
*/
dpr->dpr_stop |= DT_PROC_STOP_CREATE;
if (Pstatus(P)->pr_flags & PR_KLC)
dt_proc_stop(dpr, DT_PROC_STOP_CREATE);
else
dt_proc_stop(dpr, DT_PROC_STOP_GRAB);
if (Psetrun(P, 0, 0) == -1) {
dt_dprintf("pid %d: failed to set running: %s\n",
(int)dpr->dpr_pid, strerror(errno));
}
(void) pthread_mutex_unlock(&dpr->dpr_lock);
/*
* Wait for the process corresponding to this control thread to stop,
* process the event, and then set it running again. We want to sleep
* with dpr_lock *unheld* so that other parts of libdtrace can use the
* ps_prochandle in the meantime (e.g. ustack()). To do this, we write
* a PCWSTOP directive directly to the underlying /proc/<pid>/ctl file.
* Once the process stops, we wake up, grab dpr_lock, and then call
* Pwait() (which will return immediately) and do our processing.
*/
//printf("%s: waiting to quit\n", __func__);
while (!dpr->dpr_quit) {
const lwpstatus_t *psp;
#if defined(sun)
if (write(pfd, &wstop, sizeof (wstop)) == -1 && errno == EINTR)
continue; /* check dpr_quit and continue waiting */
#else
/* Wait for the process to report status. */
proc_wait(P);
#endif
(void) pthread_mutex_lock(&dpr->dpr_lock);
pwait_locked:
if (Pstopstatus(P, PCNULL, 0) == -1 && errno == EINTR) {
//printf("%s stopstatus (loop) pr_pid pid=%d\n", __func__, Pstatus(dpr->dpr_proc)->pr_pid);
(void) pthread_mutex_unlock(&dpr->dpr_lock);
continue; /* check dpr_quit and continue waiting */
}
switch (Pstate(P)) {
case PS_STOP:
psp = &Pstatus(P)->pr_lwp;
dt_dprintf("pid %d: proc stopped showing %d/%d\n",
pid, psp->pr_why, psp->pr_what);
#if defined(sun)
/*
* If the process stops showing PR_REQUESTED, then the
* DTrace stop() action was applied to it or another
* debugging utility (e.g. pstop(1)) asked it to stop.
* In either case, the user's intention is for the
* process to remain stopped until another external
* mechanism (e.g. prun(1)) is applied. So instead of
* setting the process running ourself, we wait for
* someone else to do so. Once that happens, we return
* to our normal loop waiting for an event of interest.
*/
if (psp->pr_why == PR_REQUESTED) {
dt_proc_waitrun(dpr);
(void) pthread_mutex_unlock(&dpr->dpr_lock);
continue;
}
/*
* If the process stops showing one of the events that
* we are tracing, perform the appropriate response.
* Note that we ignore PR_SUSPENDED, PR_CHECKPOINT, and
* PR_JOBCONTROL by design: if one of these conditions
* occurs, we will fall through to Psetrun() but the
* process will remain stopped in the kernel by the
* corresponding mechanism (e.g. job control stop).
*/
if (psp->pr_why == PR_FAULTED && psp->pr_what == FLTBPT)
dt_proc_bpmatch(dtp, dpr);
else if (psp->pr_why == PR_SYSENTRY &&
IS_SYS_FORK(psp->pr_what))
dt_proc_bpdisable(dpr);
else if (psp->pr_why == PR_SYSEXIT &&
IS_SYS_FORK(psp->pr_what))
dt_proc_bpenable(dpr);
else if (psp->pr_why == PR_SYSEXIT &&
IS_SYS_EXEC(psp->pr_what))
dt_proc_attach(dpr, B_TRUE);
#endif
//printf("In PS_STOP dpr_stop=%x\n", dpr->dpr_stop);
break;
case PS_LOST:
//printf("in PS_LOST\n");
if (Preopen(P) == 0)
goto pwait_locked;
dt_dprintf("pid %d: proc lost: %s\n",
pid, strerror(errno));
dpr->dpr_quit = B_TRUE;
notify = B_TRUE;
break;
case PS_UNDEAD:
case PS_DEAD:
dt_dprintf("pid %d: proc died\n", pid);
dpr->dpr_quit = B_TRUE;
notify = B_TRUE;
break;
}
if (Pstate(P) != PS_UNDEAD && Psetrun(P, 0, 0) == -1) {
dt_dprintf("pid %d: failed to set running: %s\n",
(int)dpr->dpr_pid, strerror(errno));
}
(void) pthread_mutex_unlock(&dpr->dpr_lock);
}
/*
* If the control thread detected PS_UNDEAD or PS_LOST, then enqueue
* the dt_proc_t structure on the dt_proc_hash_t notification list.
*/
if (notify)
dt_proc_notify(dtp, dph, dpr, NULL);
/*
* Destroy and remove any remaining breakpoints, set dpr_done and clear
* dpr_tid to indicate the control thread has exited, and notify any
* waiting thread in dt_proc_destroy() that we have succesfully exited.
*/
(void) pthread_mutex_lock(&dpr->dpr_lock);
dt_proc_bpdestroy(dpr, B_TRUE);
dpr->dpr_done = B_TRUE;
dpr->dpr_tid = 0;
(void) pthread_cond_broadcast(&dpr->dpr_cv);
(void) pthread_mutex_unlock(&dpr->dpr_lock);
return (NULL);
}
