libc: minimal: stubs getc_unlocked & getchar_unlocked

Add stub implementation and test for `getc_unlocked()` &
`getchar_unlocked()`.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>

Author: ycsin

doc/services/portability/posix/option_groups/index.rst

@@ -567,8 +567,8 @@ This table lists service support status in Zephyr for `POSIX_FD_MGMT`:
     flockfile(), yes
     ftrylockfile(), yes
     funlockfile(), yes
-    getc_unlocked(),
-    getchar_unlocked(),
+    getc_unlocked(), yes :ref:`†<posix_undefined_behaviour>`
+    getchar_unlocked(), yes :ref:`†<posix_undefined_behaviour>`
     putc_unlocked(), yes
     putchar_unlocked(), yes
 
@@ -904,8 +904,8 @@ _POSIX_THREAD_SAFE_FUNCTIONS
     flockfile(), yes
     ftrylockfile(), yes
     funlockfile(), yes
-    getc_unlocked(),
-    getchar_unlocked(),
+    getc_unlocked(), yes :ref:`†<posix_undefined_behaviour>`
+    getchar_unlocked(), yes :ref:`†<posix_undefined_behaviour>`
     getgrgid_r(),
     getgrnam_r(),
     getpwnam_r(),

lib/libc/minimal/include/stdio.h

@@ -68,6 +68,11 @@ int putc_unlocked(int c, FILE *stream);
 int putchar_unlocked(int c);
 #endif /* CONFIG_COMMON_LIBC_PUTC_UNLOCKED || __DOXYGEN__ */
 
+#if defined(CONFIG_COMMON_LIBC_GETC_UNLOCKED) || defined(__DOXYGEN__)
+int getc_unlocked(FILE *stream);
+int getchar_unlocked(void);
+#endif /* CONFIG_COMMON_LIBC_GETC_UNLOCKED || __DOXYGEN__ */
+
 #if defined(CONFIG_POSIX_FILE_LOCKING) || defined(__DOXYGEN__)
 void flockfile(FILE *file);
 int ftrylockfile(FILE *file);

lib/posix/options/file_locking.c

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#include <errno.h>
 #include <stdio.h>
 
 #include <zephyr/sys/libc-hooks.h>

tests/posix/common/src/file_locking.c

@@ -145,6 +145,24 @@ ZTEST(file_locking, test_stdio)
 	z_free_fd(POINTER_TO_INT(file));
 }
 
+/**
+ * @brief Existence test for the stubs
+ */
+ZTEST(file_locking, test_stubs)
+{
+#ifndef CONFIG_NEWLIB_LIBC
+	errno = 0;
+	zassert_equal(getchar_unlocked(), EOF);
+	zassert_equal(errno, ENOSYS);
+
+	errno = 0;
+	zassert_equal(getc_unlocked(stdin), EOF);
+	zassert_equal(errno, ENOSYS);
+#else
+	ztest_test_skip();
+#endif /* !CONFIG_NEWLIB_LIBC */
+}
+
 #else
 /**
  * PicoLIBC doesn't support these functions in its header