tests/tcg: Test that sigreturn() does not corrupt the signal mask

Add a small test to prevent regressions.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-ID: <20241108145237.37377-2-iii@linux.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tests/tcg/multiarch/Makefile.target

@@ -42,6 +42,9 @@ munmap-pthread: LDFLAGS+=-pthread
 vma-pthread: CFLAGS+=-pthread
 vma-pthread: LDFLAGS+=-pthread
 
+sigreturn-sigmask: CFLAGS+=-pthread
+sigreturn-sigmask: LDFLAGS+=-pthread
+
 # The vma-pthread seems very sensitive on gitlab and we currently
 # don't know if its exposing a real bug or the test is flaky.
 ifneq ($(GITLAB_CI),)

tests/tcg/multiarch/sigreturn-sigmask.c

@@ -0,0 +1,51 @@
+/*
+ * Test that sigreturn() does not corrupt the signal mask.
+ * Block SIGUSR2 and handle SIGUSR1.
+ * Then sigwait() SIGUSR2, which relies on it remaining blocked.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+#include <assert.h>
+#include <pthread.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+int seen_sig = -1;
+
+static void signal_func(int sig)
+{
+    seen_sig = sig;
+}
+
+static void *thread_func(void *arg)
+{
+    kill(getpid(), SIGUSR2);
+    return NULL;
+}
+
+int main(void)
+{
+    struct sigaction act = {
+        .sa_handler = signal_func,
+    };
+    pthread_t thread;
+    sigset_t set;
+    int sig;
+
+    assert(sigaction(SIGUSR1, &act, NULL) == 0);
+
+    assert(sigemptyset(&set) == 0);
+    assert(sigaddset(&set, SIGUSR2) == 0);
+    assert(sigprocmask(SIG_BLOCK, &set, NULL) == 0);
+
+    kill(getpid(), SIGUSR1);
+    assert(seen_sig == SIGUSR1);
+
+    assert(pthread_create(&thread, NULL, thread_func, NULL) == 0);
+    assert(sigwait(&set, &sig) == 0);
+    assert(sig == SIGUSR2);
+    assert(pthread_join(thread, NULL) == 0);
+
+    return EXIT_SUCCESS;
+}