Compiler warning

Compiler warning

[Koen Vandeputte]

Hi All,

I'm seeing following compiler warning during kernel compilation 
(5.0-rc5  and  4.14.96):


net/core/dev.c: In function 'validate_xmit_skb_list':
net/core/dev.c:3405:15: warning: 'tail' may be used uninitialized in 
this function [-Wmaybe-uninitialized]
     tail->next = skb;
     ~~~~~~~~~~~^~~~~


Source shows this:

https://elixir.bootlin.com/linux/v5.0-rc5/source/net/core/dev.c#L3387

Looks like "tail" can get deferenced while it indeed doesn't get 
initialized? Kind regards, Koen

Re: Compiler warning

[David Ahern]

On 2/4/19 3:43 AM, Koen Vandeputte wrote:
> Hi All,
> 
> I'm seeing following compiler warning during kernel compilation
> (5.0-rc5  and  4.14.96):
> 
> 
> net/core/dev.c: In function 'validate_xmit_skb_list':
> net/core/dev.c:3405:15: warning: 'tail' may be used uninitialized in
> this function [-Wmaybe-uninitialized]
>     tail->next = skb;
>     ~~~~~~~~~~~^~~~~
> 
> 
> Source shows this:
> 
> https://elixir.bootlin.com/linux/v5.0-rc5/source/net/core/dev.c#L3387
> 
> Looks like "tail" can get deferenced while it indeed doesn't get
> initialized? Kind regards, Koen
> 

same with this one - false positive. head is initialized to NULL. tail
is set on the first pass through the loop.

What compiler / version is this?

Re: Compiler warning

[Koen Vandeputte]

On 05.02.19 03:55, David Ahern wrote:
> On 2/4/19 3:43 AM, Koen Vandeputte wrote:
>> Hi All,
>>
>> I'm seeing following compiler warning during kernel compilation
>> (5.0-rc5  and  4.14.96):
>>
>>
>> net/core/dev.c: In function 'validate_xmit_skb_list':
>> net/core/dev.c:3405:15: warning: 'tail' may be used uninitialized in
>> this function [-Wmaybe-uninitialized]
>>      tail->next = skb;
>>      ~~~~~~~~~~~^~~~~
>>
>>
>> Source shows this:
>>
>> https://elixir.bootlin.com/linux/v5.0-rc5/source/net/core/dev.c#L3387
>>
>> Looks like "tail" can get deferenced while it indeed doesn't get
>> initialized? Kind regards, Koen
>>
> same with this one - false positive. head is initialized to NULL. tail
> is set on the first pass through the loop.
>
> What compiler / version is this?

Thanks for confirming David. (for both of the warnings)
This is seen using GCC 7.4.0

I don't know the policy upstream regarding compiler warnings .. so 
thought I should report these. :)

Regards,

Koen