kernel: Support returning termination signals from waitpid

apps/init.cpp

@@ -328,7 +328,14 @@ int main()
         {
             if (service.pid.has_value() && service.pid.value() == child)
             {
-                do_log("[init] service %s exited with status %d\n", service.name.chars(), WEXITSTATUS(status));
+                if (WIFEXITED(status))
+                {
+                    do_log("[init] service %s exited with status %d\n", service.name.chars(), WEXITSTATUS(status));
+                }
+                else
+                {
+                    do_log("[init] service %s was terminated by signal %d\n", service.name.chars(), WTERMSIG(status));
+                }
 
                 if (service.restart)
                 {

kernel/src/sys/signal.cpp

@@ -62,7 +62,7 @@ Result<u64> sys_kill(Registers*, SyscallArgs args)
     if (target->is_kernel) return 0;
     if (signo == 0) return 0;
 
-    target->pending_signals |= 1 << (signo - 1);
+    target->send_signal(signo);
 
     return 0;
 }

kernel/src/thread/Thread.cpp

@@ -4,6 +4,7 @@
 #include "thread/Scheduler.h"
 #include <bits/atfile.h>
 #include <bits/open-flags.h>
+#include <bits/waitpid.h>
 #include <luna/Alloc.h>
 #include <luna/Atomic.h>
 #include <luna/PathParser.h>
@@ -70,7 +71,7 @@ Result<SharedPtr<VFS::Inode>> Thread::resolve_atfile(int dirfd, const String& pa
     return VFS::resolve_path(path.chars(), this->auth, descriptor->inode, follow_last_symlink);
 }
 
-[[noreturn]] void Thread::exit_and_signal_parent(u8 _status)
+[[noreturn]] void Thread::exit_and_signal_parent(int _status)
 {
     if (this->id == 1) fail("the init process exited");
     if (is_kernel) state = ThreadState::Dying;
@@ -140,7 +141,8 @@ void Thread::process_pending_signals(Registers* current_regs)
                 {
                 case DefaultSignalAction::Ignore: return;
                 // FIXME: Add signal exit codes.
-                case DefaultSignalAction::Terminate: exit_and_signal_parent(255);
+                case DefaultSignalAction::Terminate: exit_and_signal_parent(signo | _SIGBIT);
+                default: return;
                 }
             }
             // If we fail to deliver the signal (usually because there's not enough space on the stack), execute the
@@ -151,6 +153,12 @@ void Thread::process_pending_signals(Registers* current_regs)
     }
 }
 
+void Thread::send_signal(int signo)
+{
+    check(signo > 0 && signo <= NSIG);
+    pending_signals |= 1 << (signo - 1);
+}
+
 bool FileDescriptor::should_append()
 {
     return flags & O_APPEND;

kernel/src/thread/Thread.h

@@ -91,7 +91,7 @@ struct Thread : public LinkedListNode<Thread>
 
     bool is_kernel { true };
 
-    u8 status { 0 };
+    int status { 0 };
 
     mode_t umask { 0 };
 
@@ -110,7 +110,7 @@ struct Thread : public LinkedListNode<Thread>
 
     PageDirectory* active_directory { nullptr };
 
-    [[noreturn]] void exit_and_signal_parent(u8 status);
+    [[noreturn]] void exit_and_signal_parent(int status);
 
     bool is_idle()
     {
@@ -144,6 +144,8 @@ struct Thread : public LinkedListNode<Thread>
     Result<u64> push_mem_on_stack(const u8* mem, usize size);
     Result<u64> pop_mem_from_stack(u8* mem, usize size);
 
+    void send_signal(int signo);
+
     static void init();
 };
 

libc/include/bits/waitpid.h

@@ -3,6 +3,8 @@
 #ifndef _BITS_WAITPID_H
 #define _BITS_WAITPID_H
 
+#define _SIGBIT 0x100
+
 #define WNOHANG 1
 
 #endif

libc/include/sys/wait.h

@@ -6,8 +6,10 @@
 #include <bits/waitpid.h>
 #include <sys/types.h>
 
-#define WIFEXITED(ret) ((ret) | 0)
+#define WIFEXITED(ret) (((ret)&_SIGBIT) == 0)
 #define WEXITSTATUS(ret) ((ret)&0xff)
+#define WIFSIGNALED(ret) (((ret)&_SIGBIT) == _SIGBIT)
+#define WTERMSIG(ret) ((ret)&0xff)
 
 #ifdef __cplusplus
 extern "C"