libc/common: Add memalign

Memalign is another name for the posix aligned_alloc function, although it
has weaker restrictions on the relationship between the alignment and size.

memalign appears to be used internally by the G++, so we need to provide an
implementation of this when using that compiler, even though it's not part
of the Zephyr C library API.

Closes: zephyrproject-rtos#57899

Signed-off-by: Keith Packard <[email protected]>

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

@@ -153,6 +153,24 @@ void *aligned_alloc(size_t alignment, size_t size)
 	return ret;
 }
 
+#if defined(CONFIG_CPP) && defined(__GNUC__)
+
+/*
+ * G++ uses this function internally for aligned allocations.
+ *
+ * Note that aligned_alloc isn't defined to work as a replacement for
+ * memalign as it requires that the size be a multiple of the alignment,
+ * while memalign does not. However, aligned alloc is just a wrapper around
+ * sys_heap_aligned_alloc which doen't have that requirement and so can be
+ * used by memalign.
+ */
+
+void *memalign(size_t alignment, size_t size)
+{
+	return aligned_alloc(alignment, size);
+}
+#endif
+
 static int malloc_prepare(void)
 {
 	void *heap_base = NULL;