platform/ptrace: log exit code for stub processes

PiperOrigin-RevId: 269631877

2 files changed, 21 insertions, 1 deletions

diff --git a/pkg/sentry/platform/ptrace/ptrace_unsafe.go b/pkg/sentry/platform/ptrace/ptrace_unsafe.go
index 47957bb3b..72c7ec564 100644
--- a/pkg/sentry/platform/ptrace/ptrace_unsafe.go
+++ b/pkg/sentry/platform/ptrace/ptrace_unsafe.go
@@ -154,3 +154,19 @@ func (t *thread) clone() (*thread, error) {
 		cpu:  ^uint32(0),
 	}, nil
 }
+
+// getEventMessage retrieves a message about the ptrace event that just happened.
+func (t *thread) getEventMessage() (uintptr, error) {
+	var msg uintptr
+	_, _, errno := syscall.RawSyscall6(
+		syscall.SYS_PTRACE,
+		syscall.PTRACE_GETEVENTMSG,
+		uintptr(t.tid),
+		0,
+		uintptr(unsafe.Pointer(&msg)),
+		0, 0)
+	if errno != 0 {
+		return msg, errno
+	}
+	return msg, nil
+}
diff --git a/pkg/sentry/platform/ptrace/subprocess.go b/pkg/sentry/platform/ptrace/subprocess.go
index 6bf7cd097..4f8f9c5d9 100644
--- a/pkg/sentry/platform/ptrace/subprocess.go
+++ b/pkg/sentry/platform/ptrace/subprocess.go
@@ -355,7 +355,8 @@ func (t *thread) wait(outcome waitOutcome) syscall.Signal {
 			}
 			if stopSig == syscall.SIGTRAP {
 				if status.TrapCause() == syscall.PTRACE_EVENT_EXIT {
-					t.dumpAndPanic("wait failed: the process exited")
+					msg, err := t.getEventMessage()
+					t.dumpAndPanic(fmt.Sprintf("wait failed: the process %d:%d exited: %x (err %v)", t.tgid, t.tid, msg, err))
 				}
 				// Re-encode the trap cause the way it's expected.
 				return stopSig | syscall.Signal(status.TrapCause()<<8)
@@ -426,6 +427,9 @@ func (t *thread) syscall(regs *syscall.PtraceRegs) (uintptr, error) {
 			break
 		} else {
 			// Some other signal caused a thread stop; ignore.
+			if sig != syscall.SIGSTOP && sig != syscall.SIGCHLD {
+				log.Warningf("The thread %d:%d has been interrupted by %d", t.tgid, t.tid, sig)
+			}
 			continue
 		}
 	}