Kernel/LibC: Cleanup, fix and implement a lot of signal code

This patch implements sigsets and some of their usages

userspace/libraries/LibC/signal.cpp

@@ -1,20 +1,67 @@
+#include <BAN/Assert.h>
 #include <signal.h>
 #include <sys/syscall.h>
 #include <unistd.h>
 
+static_assert(sizeof(sigset_t) * 8 >= _SIGMAX);
+
+int kill(pid_t pid, int sig)
+{
+	return syscall(SYS_KILL, pid, sig);
+}
+
 int raise(int sig)
 {
 	// FIXME: won't work after multithreaded
 	return kill(getpid(), sig);
 }
 
-int kill(pid_t pid, int sig)
+int sigaction(int sig, const struct sigaction* __restrict act, struct sigaction* __restrict oact)
 {
-	return syscall(SYS_KILL, pid, sig);
+	return syscall(SYS_SIGACTION, sig, act, oact);
+}
+
+int sigaddset(sigset_t* set, int signo)
+{
+	*set |= 1ull << signo;
+	return 0;
+}
+
+int sigemptyset(sigset_t* set)
+{
+	*set = 0;
+	return 0;
+}
+
+int sigfillset(sigset_t* set)
+{
+	*set = (1ull << _SIGMAX) - 1;
+	return 0;
+}
+
+int sigismember(const sigset_t* set, int signo)
+{
+	return (*set >> signo) & 1;
 }
 
 void (*signal(int sig, void (*func)(int)))(int)
 {
-	long ret = syscall(SYS_SIGNAL, sig, func);
-	return (void (*)(int))ret;
+	struct sigaction act;
+	act.sa_handler = func;
+	act.sa_flags = 0;
+
+	int ret = sigaction(sig, &act, nullptr);
+	if (ret == -1)
+		return SIG_ERR;
+	return func;
+}
+
+int sigpending(sigset_t* set)
+{
+	return syscall(SYS_SIGPENDING, set);
+}
+
+int sigprocmask(int how, const sigset_t* __restrict set, sigset_t* __restrict oset)
+{
+	return syscall(SYS_SIGPROCMASK, how, set, oset);
 }