libc: minimal: Add C11 aligned_alloc

Extend capabilities of a minimal libc to support C11 capability
to allocate memory with requested alignment.

Signed-off-by: Piotr Pryga <piotr.pryga@nordicsemi.no>

lib/libc/minimal/include/stdlib.h

@@ -23,6 +23,8 @@ long long strtoll(const char *nptr, char **endptr, int base);
 int atoi(const char *s);
 
 void *malloc(size_t size);
+void *aligned_alloc(size_t alignment, size_t size); /* From C11 */
+
 void free(void *ptr);
 void *calloc(size_t nmemb, size_t size);
 void *realloc(void *ptr, size_t size);

lib/libc/minimal/source/stdlib/malloc.c

@@ -54,6 +54,28 @@ void *malloc(size_t size)
 	return ret;
 }
 
+/* Compile in when C11 */
+#if __STDC_VERSION__ >= 201112L
+void *aligned_alloc(size_t alignment, size_t size)
+{
+	int lock_ret;
+
+	lock_ret = sys_mutex_lock(&z_malloc_heap_mutex, K_FOREVER);
+	__ASSERT_NO_MSG(lock_ret == 0);
+
+	void *ret = sys_heap_aligned_alloc(&z_malloc_heap,
+					   alignment,
+					   size);
+	if (ret == NULL && size != 0) {
+		errno = ENOMEM;
+	}
+
+	(void) sys_mutex_unlock(&z_malloc_heap_mutex);
+
+	return ret;
+}
+#endif /* __STDC_VERSION__ >= 201112L */
+
 static int malloc_prepare(const struct device *unused)
 {
 	ARG_UNUSED(unused);