[RFA] Fix splay tree KEY leak detected in GDB test gdb.base/macscp.exp

Philippe Waroquiers
2019-01-26T22:34:46Z

When a node is removed from a splay tree, the splay tree was
not using the function splay_tree_delete_key_fn to release the key.
This was causing a leak, fixed by Tom Tromey.

This patch fixes another key leak, that happens when a key equal to
a key already present is inserted. In such a case, we have to release
the old KEY.
Note that this is based on the assumption that the caller always
allocates a new KEY when doing an insert.

Also, clarify the documentation about when the release functions are
called.

include/ChangeLog
2019-01-26 Philippe Waroquiers <philippe.waroquiers@skynet.be>

* splay-tree.h (splay_tree_delete_key_fn): Update comment.
(splay_tree_delete_value_fn): Likewise.

libiberty/ChangeLog
2019-01-26 Philippe Waroquiers <philippe.waroquiers@skynet.be>

* splay-tree.c (splay_tree_insert): Also release old KEY in case
of insertion of a key equal to an already present key.
(splay_tree_new_typed_alloc): Update comment.
---
include/splay-tree.h | 11 +++++++++--
libiberty/splay-tree.c | 13 ++++++++++---
2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/include/splay-tree.h b/include/splay-tree.h
index 0d26272943..da533dec18 100644
--- a/include/splay-tree.h
+++ b/include/splay-tree.h
@@ -58,11 +58,18 @@ typedef struct splay_tree_node_s *splay_tree_node;
typedef int (*splay_tree_compare_fn) (splay_tree_key, splay_tree_key);

/* The type of a function used to deallocate any resources associated
- with the key. */
+ with the key. If you provide this function, the splay tree
+ will take the ownership of the memory of the splay_tree_key arg
+ of splay_tree_insert. This function is called to release the keys
+ present in the tree when calling splay_tree_delete or splay_tree_remove.
+ If splay_tree_insert is called with a key equal to a key already
+ present in the tree, the old key and old value will be released. */
typedef void (*splay_tree_delete_key_fn) (splay_tree_key);

/* The type of a function used to deallocate any resources associated
- with the value. */
+ with the value. If you provide this function, the memory of the
+ splay_tree_value arg of splay_tree_insert is managed similarly to
+ the splay_tree_key memory: see splay_tree_delete_key_fn. */
typedef void (*splay_tree_delete_value_fn) (splay_tree_value);

/* The type of a function used to iterate over the tree. */
diff --git a/libiberty/splay-tree.c b/libiberty/splay-tree.c
index 21d23c38df..4bbb39a62c 100644
--- a/libiberty/splay-tree.c
+++ b/libiberty/splay-tree.c
@@ -318,7 +318,11 @@ different types need to be allocated with different allocators.

The splay tree will use @var{compare_fn} to compare nodes,
@var{delete_key_fn} to deallocate keys, and @var{delete_value_fn} to
-deallocate values.
+deallocate values. Keys and values will be deallocated when the
+tree is deleted using splay_tree_delete or when a node is removed
+using splay_tree_remove. splay_tree_insert will release the previously
+inserted key and value using @var{delete_key_fn} and @var{delete_value_fn}
+if the inserted key is already found in the tree.

@end deftypefn

@@ -372,10 +376,13 @@ splay_tree_insert (splay_tree sp, splay_tree_key key, splay_tree_value value)

if (sp->root && comparison == 0)
{
- /* If the root of the tree already has the indicated KEY, just
- replace the value with VALUE. */
+ /* If the root of the tree already has the indicated KEY, delete
+ the old key and old value, and replace them with KEY and VALUE. */
+ if (sp->delete_key)
+ (*sp->delete_key) (sp->root->key);
if (sp->delete_value)
(*sp->delete_value)(sp->root->value);
+ sp->root->key = key;
sp->root->value = value;
}
else
--
2.20.1