Discard ignored signals on New Technology (#592)

libc/calls/sig.internal.h

@@ -31,6 +31,7 @@ bool __sig_handle(bool, int, int, ucontext_t *) hidden;
 int __sig_add(int, int) hidden;
 int __sig_mask(int, const sigset_t *, sigset_t *) hidden;
 int __sig_raise(int, int) hidden;
+void __sig_check_ignore(const int, const unsigned) hidden;
 
 COSMOPOLITAN_C_END_
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */

libc/calls/sig2.c

@@ -246,7 +246,7 @@ textwindows int __sig_add(int sig, int si_code) {
 }
 
 /**
- * Enqueues generic signal for delivery on New Technology.
+ * Checks for unblocked signals and delivers them on New Technology.
  *
  * @param restartable is for functions like read() but not poll()
  * @return true if EINTR should be returned by caller
@@ -264,3 +264,38 @@ textwindows bool __sig_check(bool restartable) {
   }
   return delivered;
 }
+
+/**
+ * Determines if a signal should be ignored and if so discards existing
+ * instances of said signal on New Technology.
+ *
+ * Even blocked signals are discarded.
+ *
+ * @param sig the signal number to remove
+ * @threadsafe
+ */
+textwindows void __sig_check_ignore(const int sig, const unsigned rva) {
+  struct Signal *cur, *prev, *next;
+  if (rva != (unsigned)(intptr_t)SIG_IGN &&
+      (rva != (unsigned)(intptr_t)SIG_DFL || __sig_isfatal(sig))) {
+    return;
+  }
+  if (__sig.queue) {
+    __sig_lock();
+    for (prev = 0, cur = __sig.queue; cur; cur = next) {
+      next = cur->next;
+      if (sig == cur->sig) {
+        if (cur == __sig.queue) {
+          __sig.queue = cur->next;
+        } else if (prev) {
+          prev->next = cur->next;
+        }
+        __sig_handle(false, cur->sig, cur->si_code, 0);
+        __sig_free(cur);
+      } else {
+        prev = cur;
+      }
+    }
+    __sig_unlock();
+  }
+}

libc/calls/sigaction.c

@@ -258,6 +258,7 @@ static int __sigaction(int sig, const struct sigaction *act,
     if (act) {
       __sighandrvas[sig] = rva;
       __sighandflags[sig] = act->sa_flags;
+      __sig_check_ignore(sig, rva);
     }
   }
   return rc;

test/libc/calls/sigaction_test.c

@@ -156,3 +156,22 @@ noubsan void ubsanTrumpsSystemsEngineering(void) {
 TEST(sigaction, sigFpe_handlerCanEditProcessStateAndRecoverExecution) {
   ubsanTrumpsSystemsEngineering();
 }
+
+static unsigned OnSignalCnt = 0;
+void OnSignal(int sig, siginfo_t *si, void *ctx) {
+  OnSignalCnt++;
+}
+
+TEST(sigaction, ignoringSignalDiscardsSignal) {
+  struct sigaction sa = {.sa_sigaction = OnSignal, .sa_flags = SA_SIGINFO};
+  ASSERT_EQ(0, sigaction(SIGUSR1, &sa, NULL));
+  sigset_t blocked;
+  sigemptyset(&blocked);
+  sigaddset(&blocked, SIGUSR1);
+  ASSERT_EQ(0, sigprocmask(SIG_SETMASK, &blocked, NULL));
+  ASSERT_EQ(0, raise(SIGUSR1));
+  ASSERT_NE(SIG_ERR, signal(SIGUSR1, SIG_IGN));
+  ASSERT_EQ(0, sigaction(SIGUSR1, &sa, NULL));
+  ASSERT_EQ(0, sigprocmask(SIG_UNBLOCK, &blocked, NULL));
+  EXPECT_EQ(0, OnSignalCnt);
+}