[image] Use image replacement when executing extracted images

Use image_replace() to transfer execution to the extracted image,
rather than calling image_exec() directly.  This allows the original
archive image to be freed immediately if it was marked as an
automatically freeable image (e.g. via "chain --autofree").

In particular, this ensures that in the case of an archive image
containing another archive image (such as an EFI zboot kernel wrapper
image containing a gzip-compressed kernel image), the intermediate
extracted image will be freed as early as possible, since extracted
images are always marked as automatically freeable.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/archive.c

@@ -119,9 +119,14 @@ int image_extract_exec ( struct image *image ) {
 	/* Set auto-unregister flag */
 	extracted->flags |= IMAGE_AUTO_UNREGISTER;
 
-	/* Tail-recurse into extracted image */
-	return image_exec ( extracted );
+	/* Replace current image */
+	if ( ( rc = image_replace ( extracted ) ) != 0 )
+		goto err_replace;
 
+	/* Return to allow replacement image to be executed */
+	return 0;
+
+ err_replace:
  err_set_cmdline:
 	unregister_image ( extracted );
  err_extract: