kernel+libc: Add the SA_NODEFER and SA_RESETHAND flags for sigaction()

apps/signal-test.cpp

@@ -5,16 +5,14 @@
 void handler(int)
 {
     puts("I caught a segfault!");
-
-    struct sigaction sa;
-    sa.sa_handler = SIG_DFL;
-    sigaction(SIGSEGV, &sa, NULL);
 }
 
 int main()
 {
     struct sigaction sa;
     sa.sa_handler = handler;
+    sigemptyset(&sa.sa_mask);
+    sa.sa_flags = SA_RESETHAND;
     sigaction(SIGSEGV, &sa, NULL);
 
 #pragma GCC diagnostic ignored "-Wnonnull"

kernel/src/arch/x86_64/Thread.cpp

@@ -120,8 +120,8 @@ bool Thread::deliver_signal(int signo, Registers* current_regs)
     if (push_mem_on_stack((u8*)&rsp, sizeof(u64)).has_error()) return false;
     if (push_mem_on_stack((u8*)&handler.__sa_sigreturn, sizeof(void*)).has_error()) return false;
 
-    // FIXME: Do not add the current signal to the signal mask if SA_NODEFER is set.
+    signal_mask = handler.sa_mask;
-    signal_mask = handler.sa_mask | (1 << (signo - 1));
+    if ((handler.sa_flags & SA_NODEFER) == 0) signal_mask |= (1 << (signo - 1));
 
     rsp = regs.rsp;
 
@@ -132,6 +132,14 @@ bool Thread::deliver_signal(int signo, Registers* current_regs)
 
     memcpy(current_regs, &regs, sizeof(regs));
 
+    if (handler.sa_flags & SA_RESETHAND)
+    {
+        handler.sa_handler = SIG_DFL;
+        handler.sa_mask = 0;
+        handler.sa_flags = 0;
+        signal_handlers[signo - 1] = handler;
+    }
+
     return true;
 }
 

libc/include/bits/signal.h

@@ -22,6 +22,10 @@ struct sigaction
 #endif
 };
 
+// Constants for sigaction's sa_flags field.
+#define SA_NODEFER (1 << 0)
+#define SA_RESETHAND (1 << 1)
+
 // Constants for the 'how' parameter in sigprocmask().
 #define SIG_BLOCK 0
 #define SIG_UNBLOCK 1