From 5163c5cc63c58c6c5244882a2031420d9ba20092 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Mon, 27 Jan 2020 20:47:10 +0100
Subject: [PATCH] Kernel: Expose the signal that stopped a thread via
 sys$waitpid()

---
 Kernel/Process.cpp | 8 ++++++--
 Kernel/Thread.cpp  | 2 ++
 Kernel/Thread.h    | 3 +++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/Kernel/Process.cpp b/Kernel/Process.cpp
index 47bb4d6a6d..9f62758ff4 100644
--- a/Kernel/Process.cpp
+++ b/Kernel/Process.cpp
@@ -2318,12 +2318,16 @@ pid_t Process::sys$waitpid(pid_t waitee, int* wstatus, int options)
     if (!waitee_process)
         return -ECHILD;
 
+    auto* waitee_thread = Thread::from_tid(waitee_pid);
+    if (!waitee_thread)
+        return -ECHILD;
+
     ASSERT(waitee_process);
     if (waitee_process->is_dead()) {
         exit_status = reap(*waitee_process);
     } else {
-        ASSERT(waitee_process->any_thread().state() == Thread::State::Stopped);
-        exit_status = 0x7f;
+        ASSERT(waitee_thread->state() == Thread::State::Stopped);
+        exit_status = (waitee_thread->m_stop_signal << 8) | 0x7f;
     }
 
     if (wstatus)
diff --git a/Kernel/Thread.cpp b/Kernel/Thread.cpp
index 7bba273378..20bb8878a4 100644
--- a/Kernel/Thread.cpp
+++ b/Kernel/Thread.cpp
@@ -471,6 +471,7 @@ ShouldUnblockThread Thread::dispatch_signal(u8 signal)
     m_pending_signals &= ~(1 << (signal - 1));
 
     if (signal == SIGSTOP) {
+        m_stop_signal = SIGSTOP;
         set_state(Stopped);
         return ShouldUnblockThread::No;
     }
@@ -482,6 +483,7 @@ ShouldUnblockThread Thread::dispatch_signal(u8 signal)
     if (handler_vaddr.is_null()) {
         switch (default_signal_action(signal)) {
         case DefaultSignalAction::Stop:
+            m_stop_signal = signal;
             set_state(Stopped);
             return ShouldUnblockThread::No;
         case DefaultSignalAction::DumpCore:
diff --git a/Kernel/Thread.h b/Kernel/Thread.h
index 76c6f994bd..1082a8606a 100644
--- a/Kernel/Thread.h
+++ b/Kernel/Thread.h
@@ -485,6 +485,9 @@ private:
     u32 m_priority { THREAD_PRIORITY_NORMAL };
     u32 m_extra_priority { 0 };
     u32 m_priority_boost { 0 };
+
+    u8 m_stop_signal { 0 };
+
     bool m_dump_backtrace_on_finalization { false };
     bool m_should_die { false };