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[comboot] Allow for tail recursion of COMBOOT images

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Multi-level menus via COMBOOT rely on the COMBOOT program being able
to exit and invoke a new COMBOOT program (the next menu).  This works,
but rapidly (within about five iterations) runs out of space in gPXE's
internal stack, since each new image is executed in a new function
context.

Fix by allowing tail recursion between images; an image can now
specify a replacement image for itself, and image_exec() will perform
the necessary tail recursion.
This commit is contained in:
Michael Brown
2009-02-17 00:47:35 +00:00
parent 349868b8fd
commit 8904cd55f1
8 changed files with 178 additions and 113 deletions
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30
src/core/image.c
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@@ -53,6 +53,7 @@ static void free_image ( struct refcnt *refcnt ) {
uri_put ( image->uri );
ufree ( image->data );
image_put ( image->replacement );
free ( image );
DBGC ( image, "IMAGE %p freed\n", image );
}
@@ -142,9 +143,9 @@ int register_image ( struct image *image ) {
* @v image Executable/loadable image
*/
void unregister_image ( struct image *image ) {
DBGC ( image, "IMAGE %p unregistered\n", image );
list_del ( &image->list );
image_put ( image );
DBGC ( image, "IMAGE %p unregistered\n", image );
}
/**
@@ -237,6 +238,7 @@ int image_autoload ( struct image *image ) {
* @ret rc Return status code
*/
int image_exec ( struct image *image ) {
struct image *replacement;
struct uri *old_cwuri;
int rc;
@@ -257,18 +259,40 @@ int image_exec ( struct image *image ) {
old_cwuri = uri_get ( cwuri );
churi ( image->uri );
/* Take out a temporary reference to the image. This allows
* the image to unregister itself if necessary, without
* automatically freeing itself.
*/
image_get ( image );
/* Try executing the image */
if ( ( rc = image->type->exec ( image ) ) != 0 ) {
DBGC ( image, "IMAGE %p could not execute: %s\n",
image, strerror ( rc ) );
goto done;
/* Do not return yet; we still have clean-up to do */
}
done:
/* Pick up replacement image before we drop the original
* image's temporary reference.
*/
if ( ( replacement = image->replacement ) != NULL )
image_get ( replacement );
/* Drop temporary reference to the original image */
image_put ( image );
/* Reset current working directory */
churi ( old_cwuri );
uri_put ( old_cwuri );
/* Tail-recurse into replacement image, if one exists */
if ( replacement ) {
DBGC ( image, "IMAGE %p replacing self with IMAGE %p\n",
image, replacement );
if ( ( rc = image_exec ( replacement ) ) != 0 )
return rc;
}
return rc;
}