fix error handling for pthread_sigmask

it must return errno, not -1, and should reject invalud values for how.

src/signal/sigprocmask.c

@@ -1,4 +1,5 @@
 #include <signal.h>
+#include <errno.h>
 #include "syscall.h"
 #include "libc.h"
 #include "pthread_impl.h"
@@ -11,6 +12,10 @@ int __libc_sigprocmask(int how, const sigset_t *set, sigset_t *old)
 int __sigprocmask(int how, const sigset_t *set, sigset_t *old)
 {
 	sigset_t tmp;
+	if (how > 2U) {
+		errno = EINVAL;
+		return -1;
+	}
 	/* Disallow blocking thread control signals */
 	if (set && how != SIG_UNBLOCK) {
 		tmp = *set;
@@ -22,4 +27,3 @@ int __sigprocmask(int how, const sigset_t *set, sigset_t *old)
 }
 
 weak_alias(__sigprocmask, sigprocmask);
-weak_alias(__sigprocmask, pthread_sigmask);

src/thread/pthread_sigmask.c

@@ -0,0 +1,10 @@
+#include <signal.h>
+#include <errno.h>
+#include <pthread.h>
+
+int pthread_sigmask(int how, const sigset_t *set, sigset_t *old)
+{
+	int ret = sigprocmask(how, set, old);
+	if (ret) return errno;
+	return 0;
+}