Re: [PATCH]kconfig/menu.c: fix uninitialized variable warning

[Madhavan Srinivasan <maddy@linux.vnet.ibm.com>]

On Friday 20 September 2013 01:34 AM, Yann E. MORIN wrote:
> Benjamin, All,
> 
> On 2013-09-19 15:13 -0400, Benjamin Poirier spake thusly:
>> On 2013/09/19 19:27, Yann E. MORIN wrote:
>>> Benjamin, Madhavan, All,
>>>
>>> On 2013-09-19 11:22 -0400, Benjamin Poirier spake thusly:
>>>> On 2013/09/19 12:58, Madhavan Srinivasan wrote:
>>>>> In file included from scripts/kconfig/zconf.tab.c:2537:0:
>>>>> scripts/kconfig/menu.c: In function ‘get_symbol_str’:
>>>>> scripts/kconfig/menu.c:586:18: warning: ‘jump’ may be used uninitialized in
>>>>> this function [-Wmaybe-uninitialized]
>>>>                    ^^^^^
>>>>
>>>> from gcc(1):
>>>> 	"These warnings are made optional because GCC is not smart
>>>> 	enough to see all the reasons why the code might be correct
>>>> 	despite appearing to have an error."
>>>>
>>>> I do not see this warning with gcc 4.7.2 or 4.8.1. Which version are you
>>>> using?
>>>>
>>>> The code does:
>>>>
>>>> static void get_prompt_str(struct gstr *r, struct property *prop,
>>>> [...]
>>>> 	if (head && location) {
>>>> 		jump = xmalloc(sizeof(struct jump_key));
>>>> [... different basic block ...]
>>>> 			if (head && location && menu == location)
>>>> 				jump->offset = r->len - 1;
>>>>
>>>> If the second "if" is true, then the first one was true as well, and
>>>> "jump" is initilized.
>>>
>>> Exactly what I was going to say.
>>>
>>> However:
>>>   - I believe we should strive for a warning-free code whenever possible
>>>   - while still getting help from gcc to pinpoint potential issues.
>>>
>>> Clearly, gcc is wrong here. Setting jump to NULL will cause fault if we
>>> try to dereference it. Since this should never happen given the code as
>>> it currently is, I'm slightly in favour of acking this patch.
>>>
>>> Any other reason not to apply it?
>>
>> Did you manage to get that warning as well? I didn't. If it's only from
>> old versions of gcc I'd feel better leaving the warning there than
>> masking it, in case a future code change does really introduce a use
>> before initialize.
> 
> No, I was not able to reproduce it with either gcc-4.4.7, gcc-4.6.4 or
> gcc-4.7.3 on my Ubuntu 13.04. Neither gcc-4.5 nor 4.8 are packaged, so
> I could not test them.
> 
> Anyway, -Wmaybe-uninitialized is new with 4.7. So, the warning can't
> happen with gcc < 4.7.
> 
> Madhavan, what gcc version are you using?
gcc i have is gcc version 4.8.0 20130526
> 
> Regards,
> Yann E. MORIN.
>