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[PATCH 2/7] move setting of object->type to alloc_* functions

From
Jeff King <peff@peff.net>
Date
Jul 11, 2014, 08:46 UTC
Message-ID
<20140711084611.GB5625@sigill.intra.peff.net>
In-Reply-To
<20140711084141.GA5521@sigill.intra.peff.net>

The "struct object" type implements basic object polymorphism. Individual instances are allocated as concrete types (or as a union type that can store any object), and a "struct object *" can be cast into its real type after examining its "type" enum. This means it is dangerous to have a type field that does not match the allocation (e.g., setting the type field of a "struct blob" to "OBJ_COMMIT" would mean that a reader might read past the allocated memory).

In most of the current code this is not a problem; the first thing we do after allocating an object is usually to set its type field by passing it to create_object. However, the virtual commits we create in merge-recursive.c do not ever get their type set. This does not seem to have caused problems in practice, though (presumably because we always pass around a "struct commit" pointer and never even look at the type).

We can fix this oversight and also make it harder for future code to get it wrong by setting the type directly in the object allocation functions.

This will also make it easier to fix problems with commit index allocation, as we know that any object allocated by alloc_commit_node will meet the invariant that an object with an OBJ_COMMIT type field will have a unique index number.

Signed-off-by: Jeff King <peff@peff.net>
---
 alloc.c         | 18 ++++++++++--------
 blob.c          |  2 +-
 builtin/blame.c |  1 -
 commit.c        |  2 +-
 object.c        |  5 ++---
 object.h        |  2 +-
 tag.c           |  2 +-
 tree.c          |  2 +-
 8 files changed, 17 insertions(+), 17 deletions(-)
diff --git a/alloc.c b/alloc.c
index d7c3605..fd5fcb7 100644
--- a/alloc.c
+++ b/alloc.c
@@ -18,11 +18,11 @@
 
 #define BLOCKING 1024
 
-#define DEFINE_ALLOCATOR(name, type)				\
+#define DEFINE_ALLOCATOR(name, flag, type)			\
 static struct alloc_state name##_state;				\
 void *alloc_##name##_node(void)					\
 {								\
-	return alloc_node(&name##_state, sizeof(type));		\
+	return alloc_node(&name##_state, flag, sizeof(type));	\
 }
 
 union any_object {
@@ -39,7 +39,8 @@ struct alloc_state {
 	void *p;   /* first free node in current allocation */
 };
 
-static inline void *alloc_node(struct alloc_state *s, size_t node_size)
+static inline void *alloc_node(struct alloc_state *s, enum object_type type,
+			       size_t node_size)
 {
 	void *ret;
 
@@ -52,20 +53,21 @@ static inline void *alloc_node(struct alloc_state *s, size_t node_size)
 	ret = s->p;
 	s->p = (char *)s->p + node_size;
 	memset(ret, 0, node_size);
+	((struct object *)ret)->type = type;
 	return ret;
 }
 
-DEFINE_ALLOCATOR(blob, struct blob)
-DEFINE_ALLOCATOR(tree, struct tree)
-DEFINE_ALLOCATOR(tag, struct tag)
-DEFINE_ALLOCATOR(object, union any_object)
+DEFINE_ALLOCATOR(blob, OBJ_BLOB, struct blob)
+DEFINE_ALLOCATOR(tree, OBJ_TREE, struct tree)
+DEFINE_ALLOCATOR(tag, OBJ_TAG, struct tag)
+DEFINE_ALLOCATOR(object, OBJ_NONE, union any_object)
 
 static struct alloc_state commit_state;
 
 void *alloc_commit_node(void)
 {
 	static int commit_count;
-	struct commit *c = alloc_node(&commit_state, sizeof(struct commit));
+	struct commit *c = alloc_node(&commit_state, OBJ_COMMIT, sizeof(struct commit));
 	c->index = commit_count++;
 	return c;
 }
diff --git a/blob.c b/blob.c
index ae320bd..5720a38 100644
--- a/blob.c
+++ b/blob.c
@@ -7,7 +7,7 @@ struct blob *lookup_blob(const unsigned char *sha1)
 {
 	struct object *obj = lookup_object(sha1);
 	if (!obj)
-		return create_object(sha1, OBJ_BLOB, alloc_blob_node());
+		return create_object(sha1, alloc_blob_node());
 	if (!obj->type)
 		obj->type = OBJ_BLOB;
 	if (obj->type != OBJ_BLOB) {
diff --git a/builtin/blame.c b/builtin/blame.c
index d3b256e..8f3e311 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -2287,7 +2287,6 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 	commit = alloc_commit_node();
 	commit->object.parsed = 1;
 	commit->date = now;
-	commit->object.type = OBJ_COMMIT;
 	parent_tail = &commit->parents;
 
 	if (!resolve_ref_unsafe("HEAD", head_sha1, 1, NULL))
diff --git a/commit.c b/commit.c
index fb7897c..21ed310 100644
--- a/commit.c
+++ b/commit.c
@@ -63,7 +63,7 @@ struct commit *lookup_commit(const unsigned char *sha1)
 	struct object *obj = lookup_object(sha1);
 	if (!obj) {
 		struct commit *c = alloc_commit_node();
-		return create_object(sha1, OBJ_COMMIT, c);
+		return create_object(sha1, c);
 	}
 	if (!obj->type)
 		obj->type = OBJ_COMMIT;
diff --git a/object.c b/object.c
index 9c31e9a..a950b85 100644
--- a/object.c
+++ b/object.c
@@ -141,13 +141,12 @@ static void grow_object_hash(void)
 	obj_hash_size = new_hash_size;
 }
 
-void *create_object(const unsigned char *sha1, int type, void *o)
+void *create_object(const unsigned char *sha1, void *o)
 {
 	struct object *obj = o;
 
 	obj->parsed = 0;
 	obj->used = 0;
-	obj->type = type;
 	obj->flags = 0;
 	hashcpy(obj->sha1, sha1);
 
@@ -163,7 +162,7 @@ struct object *lookup_unknown_object(const unsigned char *sha1)
 {
 	struct object *obj = lookup_object(sha1);
 	if (!obj)
-		obj = create_object(sha1, OBJ_NONE, alloc_object_node());
+		obj = create_object(sha1, alloc_object_node());
 	return obj;
 }
 
diff --git a/object.h b/object.h
index 6e12f2c..8020ace 100644
--- a/object.h
+++ b/object.h
@@ -79,7 +79,7 @@ extern struct object *get_indexed_object(unsigned int);
  */
 struct object *lookup_object(const unsigned char *sha1);
 
-extern void *create_object(const unsigned char *sha1, int type, void *obj);
+extern void *create_object(const unsigned char *sha1, void *obj);
 
 /*
  * Returns the object, having parsed it to find out what it is.
diff --git a/tag.c b/tag.c
index 7b07921..79552c7 100644
--- a/tag.c
+++ b/tag.c
@@ -40,7 +40,7 @@ struct tag *lookup_tag(const unsigned char *sha1)
 {
 	struct object *obj = lookup_object(sha1);
 	if (!obj)
-		return create_object(sha1, OBJ_TAG, alloc_tag_node());
+		return create_object(sha1, alloc_tag_node());
 	if (!obj->type)
 		obj->type = OBJ_TAG;
 	if (obj->type != OBJ_TAG) {
diff --git a/tree.c b/tree.c
index c8c49d7..ed66575 100644
--- a/tree.c
+++ b/tree.c
@@ -183,7 +183,7 @@ struct tree *lookup_tree(const unsigned char *sha1)
 {
 	struct object *obj = lookup_object(sha1);
 	if (!obj)
-		return create_object(sha1, OBJ_TREE, alloc_tree_node());
+		return create_object(sha1, alloc_tree_node());
 	if (!obj->type)
 		obj->type = OBJ_TREE;
 	if (obj->type != OBJ_TREE) {

-- 
2.0.0.566.gfe3e6b2
Previous: Jeff KingNext: Ramsay Jones
Message 8 of 35 in “alloc.c: remove the redundant commit_count variable”
  1. 2/2 alloc.c: remove the redundant commit_count variableRamsay Jones, Jul 10, 2014
  2. Jeff KingJul 11, 2014
  3. Ramsay JonesJul 11, 2014
  4. Jeff KingJul 11, 2014
  5. Ramsay JonesJul 11, 2014
  6. 0/7 ensure index is set for all OBJ_COMMIT objects variableJeff King, Jul 11, 2014
  7. 1/7 alloc.c: remove the alloc_raw_commit_node() functionJeff King, Jul 11, 2014
  8. 2/7 move setting of object->type to alloc_* functionsJeff King, Jul 11, 2014
  9. Ramsay JonesJul 12, 2014
  10. Jeff KingJul 12, 2014
  11. Jeff KingJul 13, 2014
  12. 1/8 alloc.c: remove the alloc_raw_commit_node() functionJeff King, Jul 13, 2014
  13. Junio C HamanoJul 15, 2014
  14. 2/8 alloc: write out allocator definitionsJeff King, Jul 13, 2014
  15. Junio C HamanoJul 15, 2014
  16. 3/8 move setting of object->type to alloc_* functionsJeff King, Jul 13, 2014
  17. Junio C HamanoJul 15, 2014
  18. 4/8 parse_object_buffer: do not set object typeJeff King, Jul 13, 2014
  19. 5/8 add object_as_type helper for casting objectsJeff King, Jul 13, 2014
  20. 6/8 alloc: factor out commit indexJeff King, Jul 13, 2014
  21. 7/8 object_as_type: set commit indexJeff King, Jul 13, 2014
  22. 8/8 diff-tree: avoid lookup_unknown_objectJeff King, Jul 13, 2014
  23. Ramsay JonesJul 13, 2014
  24. Jeff KingJul 14, 2014
  25. Ramsay JonesJul 14, 2014
  26. Ramsay JonesJul 12, 2014
  27. Jeff KingJul 12, 2014
  28. 3/7 parse_object_buffer: do not set object typeJeff King, Jul 11, 2014
  29. 4/7 add object_as_type helper for casting objectsJeff King, Jul 11, 2014
  30. Ramsay JonesJul 11, 2014
  31. Jeff KingJul 11, 2014
  32. 5/7 alloc: factor out commit indexJeff King, Jul 11, 2014
  33. 6/7 object_as_type: set commit indexJeff King, Jul 11, 2014
  34. 7/7 diff-tree: avoid lookup_unknown_objectJeff King, Jul 11, 2014
  35. Ramsay JonesJul 11, 2014

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