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SubjectRe: [PATCH][next] io_uring: ensure variable ret is initialized to zero
On 9/26/19 2:14 PM, Rasmus Villemoes wrote:
> On 26/09/2019 13.42, Jens Axboe wrote:
>> On 9/26/19 1:33 PM, Dan Carpenter wrote:
>>> On Thu, Sep 26, 2019 at 11:56:30AM +0200, Jens Axboe wrote:
>>>> On 9/26/19 11:50 AM, Colin King wrote:
>>>>> From: Colin Ian King <>
>>>>> In the case where sig is NULL the error variable ret is not initialized
>>>>> and may contain a garbage value on the final checks to see if ret is
>>>>> -ERESTARTSYS. Best to initialize ret to zero before the do loop to
>>>>> ensure the ret does not accidentially contain -ERESTARTSYS before the
>>>>> loop.
>>>> Oops, weird it didn't complain. I've folded in this fix, as that commit
>>>> isn't upstream yet. Thanks!
>>> There is a bug in GCC where at certain optimization levels, instead of
>>> complaining, it initializes it to zero.
>> That's awfully nice of it ;-)
>> Tried with -O0 and still didn't complain for me.
>> $ gcc --version
>> gcc (Ubuntu 9.1.0-2ubuntu2~18.04) 9.1.0
>> Tried gcc 5/6/7/8 as well. Might have to go look at what code it's
>> generating.
> I think it's essentially the same as
> (thread "tmpfs: fix uninitialized return value in shmem_link").

I think you're right, it's the same pattern. If I kill the:

if (ret)
return ret;

inside the if (sig) branch, then gcc does show the warning as it should.

Jens Axboe

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