libc/minimal: fix realloc() allocated memory alignment

The definition for realloc() says that it should return a pointer
to the allocated memory which is suitably aligned for any built-in
type.

Turn sys_heap_realloc() into a sys_heap_aligned_realloc() and use it
with __alignof__(z_max_align_t) to implement realloc() with proper
memory alignment for any platform.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>

include/sys/sys_heap.h

@@ -137,10 +137,15 @@ void sys_heap_free(struct sys_heap *h, void *mem);
  *
  * @param heap Heap from which to allocate
  * @param ptr Original pointer returned from a previous allocation
+ * @param align Alignment in bytes, must be a power of two
  * @param bytes Number of bytes requested for the new block
  * @return Pointer to memory the caller can now use, or NULL
  */
-void *sys_heap_realloc(struct sys_heap *heap, void *ptr, size_t bytes);
+void *sys_heap_aligned_realloc(struct sys_heap *heap, void *ptr,
+			       size_t align, size_t bytes);
+
+#define sys_heap_realloc(heap, ptr, bytes) \
+	sys_heap_aligned_realloc(heap, ptr, 0, bytes)
 
 /** @brief Validate heap integrity
  *

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

@@ -56,7 +56,9 @@ static int malloc_prepare(const struct device *unused)
 
 void *realloc(void *ptr, size_t requested_size)
 {
-	void *ret = sys_heap_realloc(&z_malloc_heap, ptr, requested_size);
+	void *ret = sys_heap_aligned_realloc(&z_malloc_heap, ptr,
+					     __alignof__(z_max_align_t),
+					     requested_size);
 
 	return ret == NULL ? ptr : ret;
 }

lib/os/heap.c

@@ -312,28 +312,34 @@ void *sys_heap_aligned_alloc(struct sys_heap *heap, size_t align, size_t bytes)
 	return mem;
 }
 
-void *sys_heap_realloc(struct sys_heap *heap, void *ptr, size_t bytes)
+void *sys_heap_aligned_realloc(struct sys_heap *heap, void *ptr,
+			       size_t align, size_t bytes)
 {
 	struct z_heap *h = heap->heap;
 
 	/* special realloc semantics */
 	if (ptr == NULL) {
-		return sys_heap_alloc(heap, bytes);
+		return sys_heap_aligned_alloc(heap, align, bytes);
 	}
 	if (bytes == 0) {
 		sys_heap_free(heap, ptr);
 		return NULL;
 	}
 
+	__ASSERT((align & (align - 1)) == 0, "align must be a power of 2");
+
 	if (size_too_big(h, bytes)) {
 		return NULL;
 	}
 
 	chunkid_t c = mem_to_chunkid(h, ptr);
 	chunkid_t rc = right_chunk(h, c);
-	size_t chunks_need = bytes_to_chunksz(h, bytes);
+	size_t align_gap = (uint8_t *)ptr - (uint8_t *)chunk_mem(h, c);
+	size_t chunks_need = bytes_to_chunksz(h, bytes + align_gap);
 
-	if (chunk_size(h, c) == chunks_need) {
+	if (align && ((uintptr_t)ptr & (align - 1))) {
+		/* ptr is not sufficiently aligned */
+	} else if (chunk_size(h, c) == chunks_need) {
 		/* We're good already */
 		return ptr;
 	} else if (chunk_size(h, c) > chunks_need) {
@@ -357,18 +363,18 @@ void *sys_heap_realloc(struct sys_heap *heap, void *ptr, size_t bytes)
 		merge_chunks(h, c, rc);
 		set_chunk_used(h, c, true);
 		return ptr;
-	} else {
-		/* Reallocate and copy */
-		void *ptr2 = sys_heap_alloc(heap, bytes);
+	}
 
-		if (ptr2 == NULL) {
-			return NULL;
-		}
+	/* Fallback: allocate and copy */
+	void *ptr2 = sys_heap_aligned_alloc(heap, align, bytes);
 
-		memcpy(ptr2, ptr, bytes);
-		sys_heap_free(heap, ptr);
-		return ptr2;
+	if (ptr2 == NULL) {
+		return NULL;
 	}
+
+	memcpy(ptr2, ptr, bytes);
+	sys_heap_free(heap, ptr);
+	return ptr2;
 }
 
 void sys_heap_init(struct sys_heap *heap, void *mem, size_t bytes)

tests/lib/heap/src/main.c

@@ -261,7 +261,7 @@ static void test_realloc(void)
 
 	zassert_true(sys_heap_validate(&heap), "invalid heap");
 	zassert_true(p1 != p2,
-		     "Realloc should must have moved %p", p1);
+		     "Realloc should have moved %p", p1);
 	zassert_true(realloc_check_block(p2, p2, 64), "data changed");
 	zassert_true(realloc_check_block(p3, p1, 64), "data changed");
 
@@ -290,6 +290,37 @@ static void test_realloc(void)
 		     "Realloc should have expanded in place %p -> %p",
 		     p1, p3);
 	zassert_true(realloc_check_block(p3, p1, 61), "data changed");
+
+	/* Corner case with sys_heap_aligned_realloc() on 32-bit targets
+	 * where actual memory doesn't match with given pointer
+	 * (align_gap != 0).
+	 */
+	p1 = sys_heap_aligned_alloc(&heap, 8, 32);
+	realloc_fill_block(p1, 32);
+	p2 = sys_heap_alloc(&heap, 32);
+	realloc_fill_block(p2, 32);
+	p3 = sys_heap_aligned_realloc(&heap, p1, 8, 36);
+
+	zassert_true(sys_heap_validate(&heap), "invalid heap");
+	zassert_true(realloc_check_block(p3, p1, 32), "data changed");
+	zassert_true(realloc_check_block(p2, p2, 32), "data changed");
+	realloc_fill_block(p3, 36);
+	zassert_true(sys_heap_validate(&heap), "invalid heap");
+	zassert_true(p1 != p3,
+		     "Realloc should have moved %p", p1);
+
+	/* Test realloc with increasing alignment */
+	p1 = sys_heap_aligned_alloc(&heap, 32, 32);
+	p2 = sys_heap_aligned_alloc(&heap, 8, 32);
+	p3 = sys_heap_aligned_realloc(&heap, p2, 8, 16);
+	zassert_true(sys_heap_validate(&heap), "invalid heap");
+	zassert_true(p2 == p3,
+		     "Realloc should have expanded in place %p -> %p",
+		     p2, p3);
+	p3 = sys_heap_aligned_alloc(&heap, 32, 8);
+	zassert_true(sys_heap_validate(&heap), "invalid heap");
+	zassert_true(p2 != p3,
+		     "Realloc should have moved %p", p2);
 }
 
 void test_main(void)