detach(): warn if we see ECHILD from waitpid
* strace.c (detach): Warn if we see ECHILD from waitpid.
Explain in comments that we don't normally expect !WIFSTOPPED
either, and also that PTRACE_CONT failure isn't expected
(the "break" there is a "I'm confused, bailing out" code style)..
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
diff --git a/strace.c b/strace.c
index ae24db1..89e89bc 100644
--- a/strace.c
+++ b/strace.c
@@ -764,7 +764,7 @@
}
else if (errno != ESRCH) {
/* Shouldn't happen. */
- perror_msg("detach: ptrace(%u,PTRACE_DETACH)", tcp->pid);
+ perror_msg("detach: ptrace(PTRACE_DETACH,%u)", tcp->pid);
}
else
/* ESRCH: process is either not stopped or doesn't exist. */
@@ -789,7 +789,7 @@
if (!error)
interrupt_done = 1;
else if (errno != ESRCH)
- perror_msg("detach: ptrace(%u,PTRACE_INTERRUPT)", tcp->pid);
+ perror_msg("detach: ptrace(PTRACE_INTERRUPT,%u)", tcp->pid);
}
else {
error = my_tkill(tcp->pid, SIGSTOP);
@@ -807,13 +807,25 @@
if (waitpid(tcp->pid, &status, __WALL) < 0) {
if (errno == EINTR)
continue;
- if (errno == ECHILD) /* Already gone. */
- break;
+ /*
+ * 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)) {
- /* Au revoir, mon ami. */
+ /*
+ * 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);
@@ -859,8 +871,13 @@
sig = 0;
/* Can't detach just yet, may need to wait for SIGSTOP */
error = ptrace_restart(PTRACE_CONT, tcp, sig);
- if (error < 0)
+ 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;
+ }
}
}