sandbox: Improve/augment memory allocation functions

Implement realloc() and free() for sandbox, by adding a header to each
block which contains the block size.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Che-Liang Chiou <clchiou@chromium.org>
Reviewed-by: Hung-ying Tyan <tyanh@chromium.org>

arch/sandbox/cpu/os.c

@@ -27,6 +27,10 @@
 
 /* Operating System Interface */
 
+struct os_mem_hdr {
+	size_t length;		/* number of bytes in the block */
+};
+
 ssize_t os_read(int fd, void *buf, size_t count)
 {
 	return read(fd, buf, count);
@@ -128,8 +132,45 @@ void os_tty_raw(int fd)
 
 void *os_malloc(size_t length)
 {
-	return mmap(NULL, length, PROT_READ | PROT_WRITE,
-			MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	struct os_mem_hdr *hdr;
+
+	hdr = mmap(NULL, length + sizeof(*hdr), PROT_READ | PROT_WRITE,
+		   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	if (hdr == MAP_FAILED)
+		return NULL;
+	hdr->length = length;
+
+	return hdr + 1;
+}
+
+void *os_free(void *ptr)
+{
+	struct os_mem_hdr *hdr = ptr;
+
+	hdr--;
+	if (ptr)
+		munmap(hdr, hdr->length + sizeof(*hdr));
+}
+
+void *os_realloc(void *ptr, size_t length)
+{
+	struct os_mem_hdr *hdr = ptr;
+	void *buf = NULL;
+
+	hdr--;
+	if (length != 0) {
+		buf = os_malloc(length);
+		if (!buf)
+			return buf;
+		if (ptr) {
+			if (length > hdr->length)
+				length = hdr->length;
+			memcpy(buf, ptr, length);
+		}
+	}
+	os_free(ptr);
+
+	return buf;
 }
 
 void os_usleep(unsigned long usec)

include/os.h

@@ -106,6 +106,35 @@ void os_tty_raw(int fd);
  */
 void *os_malloc(size_t length);
 
+/**
+ * Free memory previous allocated with os_malloc()/os_realloc()
+ *
+ * This returns the memory to the OS.
+ *
+ * \param ptr		Pointer to memory block to free
+ */
+void *os_free(void *ptr);
+
+/**
+ * Reallocate previously-allocated memory to increase/decrease space
+ *
+ * This works in a similar way to the C library realloc() function. If
+ * length is 0, then ptr is freed. Otherwise the space used by ptr is
+ * expanded or reduced depending on whether length is larger or smaller
+ * than before.
+ *
+ * If ptr is NULL, then this is similar to calling os_malloc().
+ *
+ * This function may need to move the memory block to make room for any
+ * extra space, in which case the new pointer is returned.
+ *
+ * \param ptr		Pointer to memory block to reallocate
+ * \param length	New length for memory block
+ * \return pointer to new memory block, or NULL on failure or if length
+ *	is 0.
+ */
+void *os_realloc(void *ptr, size_t length);
+
 /**
  * Access to the usleep function of the os
  *