[ovs-dev] [PATCH] netdev-vport: Fix compilation warning

Kevin Traynor ktraynor at redhat.com
Wed Nov 17 15:45:16 UTC 2021


On 17/11/2021 14:44, Eelco Chaudron wrote:
> 
> 
> On 17 Nov 2021, at 14:00, Roi Dayan via dev wrote:
> 
>> On 2021-11-17 2:51 PM, Roi Dayan wrote:
>>>
>>>
>>> On 2021-11-17 2:42 PM, Roi Dayan wrote:
>>>>
>>>>
>>>> On 2021-11-17 2:23 PM, Roi Dayan wrote:
>>>>>
>>>>>
>>>>> On 2021-11-17 2:17 PM, David Marchand wrote:
>>>>>> On Wed, Nov 17, 2021 at 1:12 PM Roi Dayan via dev
>>>>>> <ovs-dev at openvswitch.org> wrote:
>>>>>>>
>>>>>>> port is declared as uint16 so use %hu specifier instead of %d.
>>>>>>>
>>>>>>> lib/netdev-vport.c:460:44: error: '%s' directive output may be truncated writing up to 4 bytes into a region of size between 1 and 10 [-Werror=format-truncation=]
>>>>>>>         snprintf(namebuf, bufsize, "dst_port_%d%s",
>>>>>>>                                              ^~
>>>>>>
>>>>>> Out of curiosity, is it due to new checks from a recent compiler?
>>>>>
>>>>> do you mean if we updated the compiler? than no.
>>>>> it fails on powerpc machine.
>>>>>
>>>>>>
>>>>>>
>>>>>>> Fixes: 189de33f02b2 ("netdev-vport: reject concomitant incompatible tunnels")
>>>>>>> Signed-off-by: Roi Dayan <roid at nvidia.com>
>>>>>>> Reviewed-by: Eli Britstein <elibr at nvidia.com>
>>>>>>> ---
>>>>>>>    lib/netdev-vport.c | 2 +-
>>>>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/lib/netdev-vport.c b/lib/netdev-vport.c
>>>>>>> index 499c0291c933..1c7f55757e9a 100644
>>>>>>> --- a/lib/netdev-vport.c
>>>>>>> +++ b/lib/netdev-vport.c
>>>>>>> @@ -457,7 +457,7 @@ static char *
>>>>>>>    vxlan_get_port_ext_gbp_str(uint16_t port, bool gbp,
>>>>>>>                               char namebuf[], size_t bufsize)
>>>>>>>    {
>>>>>>> -    snprintf(namebuf, bufsize, "dst_port_%d%s",
>>>>>>> +    snprintf(namebuf, bufsize, "dst_port_%hu%s",
>>>>>>>                 port, gbp ? "_gbp" : "");
>>>>>>
>>>>>> Format for uint16_t is PRIu16.
>>>>>
>>>>> tested PRIu16 and got the same error. isn't PRIu16 defined as "u" ?
>>>>>
>>>>
>>>> did some more tests.
>>>> the test machine is ppc64be.
>>>>
>>>> lib/netdev-vport.c:460:51: note: format string is defined here
>>>>        snprintf(namebuf, bufsize, "dst_port_%"PRIu16"%s",
>>>>                                                      ^~
>>>>
>>>> seems the compiler now complains on the string.
>>>> if i remove the string the compiler doesn't complain with either %d
>>>> or PRIu16.
>>>
>>> seems i got it wrong. the compiler identify the size passed is 20.
>>> %hu solved it by limiting the number and have room for the string "_gbp".
>>> using PRIu16 is bigger than %hu allowing to pass the 20 chars size.
>>> i'll send a diff fix increasing the buf size to 24 and using PRIu16
>>> as should.
>>>
>>> thanks for the review.
>>>
>>>
>>
>> before submitting i'm trying to understand why the compiler suggests 24.
>> "dst_port_" is 9 and the port could be 2. then "_gbp" is 4. so 20
>> should be enough. someone has an idea?
>> I can reproduce the issue only on ppc64be.
> 
> Don’t have a ppc64be compiler ready, but what is the size of an int on that architecture?
> %d normally is an int, so if 32 bit the max value for the string could be strlen(“-2147483648”).
> 

There is an INT_STRLEN() macro in 
https://github.com/openvswitch/ovs/blob/master/include/openvswitch/type-props.h 
which is used elsewhere in the code and might be useful here.

> //Eelco
> 
> 
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