[PATCH 2/2] selftests/nolibc: add a test for errx()

[Danish Khateeb <danishkhateeb03@gmail.com>]

nolibc-test does not call any of the err.h functions, so nothing
noticed that verrx(), and errx() through it, printed their messages
with the wrong arguments, or crashed.

Add a test that calls errx() in a child with stderr redirected to a
pipe, and checks the exit status and the message.

Assisted-by: LLM
Signed-off-by: Danish Khateeb <danishkhateeb03@gmail.com>
---
 tools/testing/selftests/nolibc/nolibc-test.c | 47 ++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index 37c11a7fce23..1447c2e39af5 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -32,6 +32,7 @@
 #include <sys/utsname.h>
 #include <sys/wait.h>
 #include <dirent.h>
+#include <err.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <poll.h>
@@ -2223,6 +2224,51 @@ int test_asprintf(void)
 	return 0;
 }
 
+int test_errx(void)
+{
+	char buf[100], expected[100];
+	int pipefd[2], status;
+	ssize_t len;
+	pid_t pid;
+
+	if (pipe(pipefd) == -1)
+		return 1;
+
+	/* flush the printf buffer to avoid child flush it */
+	fflush(stdout);
+	fflush(stderr);
+
+	pid = fork();
+	if (pid == -1) {
+		close(pipefd[0]);
+		close(pipefd[1]);
+		return 2;
+	}
+
+	if (pid == 0) {
+		dup2(pipefd[1], STDERR_FILENO);
+		errx(42, "%d %s", 1234, "foo");
+	}
+
+	close(pipefd[1]);
+	pid = waitpid(pid, &status, 0);
+	len = read(pipefd[0], buf, sizeof(buf) - 1);
+	close(pipefd[0]);
+
+	if (pid == -1 || !WIFEXITED(status) || WEXITSTATUS(status) != 42)
+		return 3;
+
+	if (len == -1)
+		return 4;
+	buf[len] = 0;
+
+	snprintf(expected, sizeof(expected), "%s: 1234 foo\n", program_invocation_short_name);
+	if (strcmp(buf, expected) != 0)
+		return 5;
+
+	return 0;
+}
+
 static int run_printf(int min, int max)
 {
 	int test;
@@ -2287,6 +2333,7 @@ static int run_printf(int min, int max)
 		CASE_TEST(scanf);        EXPECT_ZR(1, test_scanf()); break;
 		CASE_TEST(printf_error); EXPECT_ZR(1, test_printf_error()); break;
 		CASE_TEST(asprintf);     EXPECT_ZR(1, test_asprintf()); break;
+		CASE_TEST(errx);         EXPECT_ZR(1, test_errx()); break;
 		case __LINE__:
 			return ret; /* must be last */
 		/* note: do not set any defaults so as to permit holes above */
-- 
2.55.0