On 2018/12/5 下午9:40, David Sterba wrote:
> On Wed, Dec 05, 2018 at 02:40:12PM +0800, Qu Wenruo wrote:
>> 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;
>>
>> It's possible that compiler doesn't get enough hint for BUG_ON() on
>> lowest_level + 1 >= BTRFS_MAX_LEVEL case.
>>
>> Fix it by using a do {} while() loop other than while() {} loop, to
>> ensure we will run the loop for at least once.
>
> I was hoping that we can actually add the hint to BUG_ON so the code
> does not continue if the condition is true.
>
I checked that method, but I'm not that confident about things like:
bugon_trace()
{
if (!val)
return;
__bugon_trace();
}
__attribute__ ((noreturn))
static inline void __bugon_trace();
This is as simple as just one extra function call, but the original
problem is just one more function call before hitting abort().
So I just give up screwing up things I'm not comfort enough to tweaking.
The current do {} while() loop is the most direct solution, if gcc one
day still gives such warning then I could say some harsh word then.
Thanks,
Qu
signature.asc
Description: OpenPGP digital signature
