"maybe" pointer in 'struct commit' is tricky because it can be lazily
initialized to take advantage of commit-graph if available. This makes
it not safe to access directly.
This leads to a rule in commit.cocci to rewrite 'x->maybe_tree' to
'get_commit_tree(x)'. But that rule alone could lead to incorrectly
rewrite assignments, e.g. from
x->maybe_tree = yes
to
get_commit_tree(x) = yes
Because of this we have a second rule to revert this effect. Szeder
found out that we could do better by performing the assignment rewrite
rule first, then the remaining is read-only access and handled by the
current first rule.
For this to work, we need to transform "x->maybe_tree = y" to something
that does NOT contain "x->maybe_tree" to avoid the original first
rule. This is where set_commit_tree() comes in.
Helped-by: SZEDER Gábor <[email protected]>
Helped-by: Johannes Schindelin <[email protected]>
Signed-off-by: Nguyễn Thái Ngọc Duy <[email protected]>
---
commit-graph.c | 9 +++++++--
commit.c | 9 +++++++--
contrib/coccinelle/commit.cocci | 20 +++++++++++++-------
merge-recursive.c | 7 ++++++-
4 files changed, 33 insertions(+), 12 deletions(-)
diff --git a/commit-graph.c b/commit-graph.c
index 47e9be0a3a..155a270457 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -343,6 +343,11 @@ static void fill_commit_graph_info(struct commit *item,
struct commit_graph *g,
item->generation = get_be32(commit_data + g->hash_len + 8) >> 2;
}
+static inline void set_commit_tree(struct commit *c, struct tree *t)
+{
+ c->maybe_tree = t;
+}
+
static int fill_commit_in_graph(struct repository *r,
struct commit *item,
struct commit_graph *g, uint32_t pos)
@@ -356,7 +361,7 @@ static int fill_commit_in_graph(struct repository *r,
item->object.parsed = 1;
item->graph_pos = pos;
- item->maybe_tree = NULL;
+ set_commit_tree(item, NULL);
date_high = get_be32(commit_data + g->hash_len + 8) & 0x3;
date_low = get_be32(commit_data + g->hash_len + 12);
@@ -442,7 +447,7 @@ static struct tree *load_tree_for_commit(struct repository
*r,
GRAPH_DATA_WIDTH * (c->graph_pos);
hashcpy(oid.hash, commit_data);
- c->maybe_tree = lookup_tree(r, &oid);
+ set_commit_tree(c, lookup_tree(r, &oid));
return c->maybe_tree;
}
diff --git a/commit.c b/commit.c
index a5333c7ac6..043ba64f17 100644
--- a/commit.c
+++ b/commit.c
@@ -340,6 +340,11 @@ void free_commit_buffer(struct parsed_object_pool *pool,
struct commit *commit)
}
}
+static inline void set_commit_tree(struct commit *c, struct tree *t)
+{
+ c->maybe_tree = t;
+}
+
struct tree *get_commit_tree(const struct commit *commit)
{
if (commit->maybe_tree || !commit->object.parsed)
@@ -358,7 +363,7 @@ struct object_id *get_commit_tree_oid(const struct commit
*commit)
void release_commit_memory(struct parsed_object_pool *pool, struct commit *c)
{
- c->maybe_tree = NULL;
+ set_commit_tree(c, NULL);
c->index = 0;
free_commit_buffer(pool, c);
free_commit_list(c->parents);
@@ -406,7 +411,7 @@ int parse_commit_buffer(struct repository *r, struct commit
*item, const void *b
if (get_oid_hex(bufptr + 5, &parent) < 0)
return error("bad tree pointer in commit %s",
oid_to_hex(&item->object.oid));
- item->maybe_tree = lookup_tree(r, &parent);
+ set_commit_tree(item, lookup_tree(r, &parent));
bufptr += tree_entry_len + 1; /* "tree " + "hex sha1" + "\n" */
pptr = &item->parents;
diff --git a/contrib/coccinelle/commit.cocci b/contrib/coccinelle/commit.cocci
index c49aa558f0..663658a127 100644
--- a/contrib/coccinelle/commit.cocci
+++ b/contrib/coccinelle/commit.cocci
@@ -10,19 +10,25 @@ expression c;
- c->maybe_tree->object.oid.hash
+ get_commit_tree_oid(c)->hash
-// These excluded functions must access c->maybe_tree direcly.
@@
-identifier f !~
"^(get_commit_tree|get_commit_tree_in_graph_one|load_tree_for_commit)$";
+identifier f !~ "^set_commit_tree$";
expression c;
+expression s;
@@
f(...) {<...
-- c->maybe_tree
-+ get_commit_tree(c)
+- c->maybe_tree = s
++ set_commit_tree(c, s)
...>}
+// These excluded functions must access c->maybe_tree direcly.
+// Note that if c->maybe_tree is written somewhere outside of these
+// functions, then the recommended transformation will be bogus with
+// get_commit_tree() on the LHS.
@@
+identifier f !~
"^(get_commit_tree|get_commit_tree_in_graph_one|load_tree_for_commit|set_commit_tree)$";
expression c;
-expression s;
@@
-- get_commit_tree(c) = s
-+ c->maybe_tree = s
+ f(...) {<...
+- c->maybe_tree
++ get_commit_tree(c)
+ ...>}
diff --git a/merge-recursive.c b/merge-recursive.c
index 6c40c61c47..ca4731a719 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -163,6 +163,11 @@ static struct tree *shift_tree_object(struct repository
*repo,
return lookup_tree(repo, &shifted);
}
+static inline void set_commit_tree(struct commit *c, struct tree *t)
+{
+ c->maybe_tree = t;
+}
+
static struct commit *make_virtual_commit(struct repository *repo,
struct tree *tree,
const char *comment)
@@ -170,7 +175,7 @@ static struct commit *make_virtual_commit(struct repository
*repo,
struct commit *commit = alloc_commit_node(repo);
set_merge_remote_desc(commit, comment, (struct object *)commit);
- commit->maybe_tree = tree;
+ set_commit_tree(commit, tree);
commit->object.parsed = 1;
return commit;
}
--
2.21.0.682.g30d2204636
