detach(struct tcb *tcp)
{
int error;
- int status, sigstop_expected, interrupt_done;
+ int status;
if (tcp->flags & TCB_BPTSET)
clearbpt(tcp);
# define PTRACE_DETACH PTRACE_SUNDETACH
#endif
- error = 0;
- sigstop_expected = 0;
- interrupt_done = 0;
- if (tcp->flags & TCB_ATTACHED) {
+ if (!(tcp->flags & TCB_ATTACHED))
+ goto drop;
+
+ /* We attached but possibly didn't see the expected SIGSTOP.
+ * We must catch exactly one as otherwise the detached process
+ * would be left stopped (process state T).
+ */
+ if (tcp->flags & TCB_IGNORE_ONE_SIGSTOP)
+ goto wait_loop;
+
+ error = ptrace(PTRACE_DETACH, tcp->pid, 0, 0);
+ if (!error) {
+ /* On a clear day, you can see forever. */
+ goto drop;
+ }
+ if (errno != ESRCH) {
+ /* Shouldn't happen. */
+ perror_msg("detach: ptrace(PTRACE_DETACH,%u)", tcp->pid);
+ goto drop;
+ }
+ /* ESRCH: process is either not stopped or doesn't exist. */
+ if (my_tkill(tcp->pid, 0) < 0) {
+ if (errno != ESRCH)
+ /* Shouldn't happen. */
+ perror_msg("detach: tkill(%u,0)", tcp->pid);
+ /* else: process doesn't exist. */
+ goto drop;
+ }
+ /* Process is not stopped, need to stop it. */
+ if (use_seize) {
/*
- * We attached but possibly didn't see the expected SIGSTOP.
- * We must catch exactly one as otherwise the detached process
- * would be left stopped (process state T).
+ * With SEIZE, tracee can be in group-stop already.
+ * In this state sending it another SIGSTOP does nothing.
+ * Need to use INTERRUPT.
+ * Testcase: trying to ^C a "strace -p <stopped_process>".
*/
- sigstop_expected = (tcp->flags & TCB_IGNORE_ONE_SIGSTOP);
- if (sigstop_expected)
+ error = ptrace(PTRACE_INTERRUPT, tcp->pid, 0, 0);
+ if (!error)
goto wait_loop;
- error = ptrace(PTRACE_DETACH, tcp->pid, 0, 0);
- if (error == 0) {
- /* On a clear day, you can see forever. */
- }
- else if (errno != ESRCH) {
- /* Shouldn't happen. */
- perror_msg("detach: ptrace(PTRACE_DETACH,%u)", tcp->pid);
- }
- else
- /* ESRCH: process is either not stopped or doesn't exist. */
- if (my_tkill(tcp->pid, 0) < 0) {
- if (errno != ESRCH)
- /* Shouldn't happen. */
- perror_msg("detach: tkill(%u,0)", tcp->pid);
- /* else: process doesn't exist. */
- }
- else
- /* Process is not stopped. */
- if (!sigstop_expected) {
- /* We need to stop it. */
- if (use_seize) {
- /*
- * With SEIZE, tracee can be in group-stop already.
- * In this state sending it another SIGSTOP does nothing.
- * Need to use INTERRUPT.
- * Testcase: trying to ^C a "strace -p <stopped_process>".
- */
- error = ptrace(PTRACE_INTERRUPT, tcp->pid, 0, 0);
- if (!error)
- interrupt_done = 1;
- else if (errno != ESRCH)
- perror_msg("detach: ptrace(PTRACE_INTERRUPT,%u)", tcp->pid);
- }
- else {
- error = my_tkill(tcp->pid, SIGSTOP);
- if (!error)
- sigstop_expected = 1;
- else if (errno != ESRCH)
- perror_msg("detach: tkill(%u,SIGSTOP)", tcp->pid);
- }
- }
+ if (errno != ESRCH)
+ perror_msg("detach: ptrace(PTRACE_INTERRUPT,%u)", tcp->pid);
}
+ else {
+ error = my_tkill(tcp->pid, SIGSTOP);
+ if (!error)
+ goto wait_loop;
+ if (errno != ESRCH)
+ perror_msg("detach: tkill(%u,SIGSTOP)", tcp->pid);
+ }
+ /* Either process doesn't exist, or some weird error. */
+ goto drop;
- if (sigstop_expected || interrupt_done) {
wait_loop:
- for (;;) {
- int sig;
- if (waitpid(tcp->pid, &status, __WALL) < 0) {
- if (errno == EINTR)
- continue;
- /*
- * if (errno == ECHILD) break;
- * ^^^ WRONG! We expect this PID to exist,
- * and want to emit a message otherwise:
- */
- perror_msg("detach: waitpid(%u)", tcp->pid);
- break;
- }
- if (!WIFSTOPPED(status)) {
- /*
- * Tracee exited or was killed by signal.
- * We shouldn't normally reach this place:
- * we don't want to consume exit status.
- * Consider "strace -p PID" being ^C-ed:
- * we want merely to detach from PID.
- *
- * However, we _can_ end up here if tracee
- * was SIGKILLed.
- */
- break;
- }
- sig = WSTOPSIG(status);
- if (debug_flag)
- fprintf(stderr, "detach wait: event:%d sig:%d\n",
- (unsigned)status >> 16, sig);
- if (sigstop_expected && sig == SIGSTOP) {
- /* Detach, suppressing SIGSTOP */
- ptrace_restart(PTRACE_DETACH, tcp, 0);
- break;
- }
- if (interrupt_done) {
- unsigned event = (unsigned)status >> 16;
- if (event == PTRACE_EVENT_STOP /*&& sig == SIGTRAP*/) {
- /*
- * sig == SIGTRAP: PTRACE_INTERRUPT stop.
- * sig == other: process was already stopped
- * with this stopping sig (see tests/detach-stopped).
- * Looks like re-injecting this sig is not necessary
- * in DETACH for the tracee to remain stopped.
- */
- sig = 0;
- }
+ /* We end up here in three cases:
+ * 1. We sent PTRACE_INTERRUPT (use_seize case)
+ * 2. We sent SIGSTOP (!use_seize)
+ * 3. Attach SIGSTOP was already pending (TCB_IGNORE_ONE_SIGSTOP set)
+ */
+ for (;;) {
+ int sig;
+ if (waitpid(tcp->pid, &status, __WALL) < 0) {
+ if (errno == EINTR)
+ continue;
+ /*
+ * if (errno == ECHILD) break;
+ * ^^^ WRONG! We expect this PID to exist,
+ * and want to emit a message otherwise:
+ */
+ perror_msg("detach: waitpid(%u)", tcp->pid);
+ break;
+ }
+ if (!WIFSTOPPED(status)) {
+ /*
+ * Tracee exited or was killed by signal.
+ * We shouldn't normally reach this place:
+ * we don't want to consume exit status.
+ * Consider "strace -p PID" being ^C-ed:
+ * we want merely to detach from PID.
+ *
+ * However, we _can_ end up here if tracee
+ * was SIGKILLed.
+ */
+ break;
+ }
+ sig = WSTOPSIG(status);
+ if (debug_flag)
+ fprintf(stderr, "detach wait: event:%d sig:%d\n",
+ (unsigned)status >> 16, sig);
+ if (use_seize) {
+ unsigned event = (unsigned)status >> 16;
+ if (event == PTRACE_EVENT_STOP /*&& sig == SIGTRAP*/) {
/*
- * PTRACE_INTERRUPT is not guaranteed to produce
- * the above event if other ptrace-stop is pending.
- * See tests/detach-sleeping testcase:
- * strace got SIGINT while tracee is sleeping.
- * We sent PTRACE_INTERRUPT.
- * We see syscall exit, not PTRACE_INTERRUPT stop.
- * We won't get PTRACE_INTERRUPT stop
- * if we would CONT now. Need to DETACH.
- */
- if (sig == syscall_trap_sig)
- sig = 0;
- /* else: not sure in which case we can be here.
- * Signal stop? Inject it while detaching.
+ * sig == SIGTRAP: PTRACE_INTERRUPT stop.
+ * sig == other: process was already stopped
+ * with this stopping sig (see tests/detach-stopped).
+ * Looks like re-injecting this sig is not necessary
+ * in DETACH for the tracee to remain stopped.
*/
- ptrace_restart(PTRACE_DETACH, tcp, sig);
- break;
+ sig = 0;
}
+ /*
+ * PTRACE_INTERRUPT is not guaranteed to produce
+ * the above event if other ptrace-stop is pending.
+ * See tests/detach-sleeping testcase:
+ * strace got SIGINT while tracee is sleeping.
+ * We sent PTRACE_INTERRUPT.
+ * We see syscall exit, not PTRACE_INTERRUPT stop.
+ * We won't get PTRACE_INTERRUPT stop
+ * if we would CONT now. Need to DETACH.
+ */
if (sig == syscall_trap_sig)
sig = 0;
- /* Can't detach just yet, may need to wait for SIGSTOP */
- error = ptrace_restart(PTRACE_CONT, tcp, sig);
- if (error < 0) {
- /* Should not happen.
- * Note: ptrace_restart returns 0 on ESRCH, so it's not it.
- * ptrace_restart already emitted error message.
- */
- break;
- }
+ /* else: not sure in which case we can be here.
+ * Signal stop? Inject it while detaching.
+ */
+ ptrace_restart(PTRACE_DETACH, tcp, sig);
+ break;
+ }
+ /* Note: this check has to be after use_seize check */
+ /* (else, in use_seize case SIGSTOP will be mistreated) */
+ if (sig == SIGSTOP) {
+ /* Detach, suppressing SIGSTOP */
+ ptrace_restart(PTRACE_DETACH, tcp, 0);
+ break;
+ }
+ if (sig == syscall_trap_sig)
+ sig = 0;
+ /* Can't detach just yet, may need to wait for SIGSTOP */
+ error = ptrace_restart(PTRACE_CONT, tcp, sig);
+ if (error < 0) {
+ /* Should not happen.
+ * Note: ptrace_restart returns 0 on ESRCH, so it's not it.
+ * ptrace_restart already emitted error message.
+ */
+ break;
}
}
+ drop:
if (!qflag && (tcp->flags & TCB_ATTACHED))
fprintf(stderr, "Process %u detached\n", tcp->pid);
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