GCC 8.2.1 will report the following warning with "make W=1":
ctree.c: In function 'btrfs_next_sibling_tree_block':
ctree.c:2990:21: warning: 'slot' may be used uninitialized in this function [-Wmaybe-uninitialized]
path->slots[level] = slot;
~~~~~~~~~~~~~~~~~~~^~~~~~
The culprit is the following code:
int slot; << Not initialized
int level = path->lowest_level + 1;
BUG_ON(path->lowest_level + 1 >= BTRFS_MAX_LEVEL);
while(level < BTRFS_MAX_LEVEL) {
slot = path->slots[level] + 1;
^^^^^^ but we initialize @slot here.
...
}
path->slots[level] = slot;
Again, it's the stupid compiler needs some hint for the fact that
we will always enter the while loop for at least once, thus @slot should
always be initialized.
Fix it by assign level after the BUG_ON(), so the stupid compiler knows
we will always go into the while loop.
Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
---
changelog:
v1.1:
Better commit message, with the original warning report and
how compiler thinks this could be a problem.
---
ctree.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/ctree.c b/ctree.c
index 46e2ccedc0bf..9c9cb0dfdbf2 100644
--- a/ctree.c
+++ b/ctree.c
@@ -2961,11 +2961,12 @@ int btrfs_next_sibling_tree_block(struct btrfs_fs_info *fs_info,
struct btrfs_path *path)
{
int slot;
- int level = path->lowest_level + 1;
+ int level;
struct extent_buffer *c;
struct extent_buffer *next = NULL;
BUG_ON(path->lowest_level + 1 >= BTRFS_MAX_LEVEL);
+ level = path->lowest_level + 1;
while(level < BTRFS_MAX_LEVEL) {
if (!path->nodes[level])
return 1;
--
2.19.1
