Re: [V2][PATCH 1/1] Add a new warning option -Wstrict-flex-arrays.

[Qing Zhao <qing.zhao@oracle.com>]

> On Dec 2, 2022, at 2:20 AM, Richard Biener <rguenther@suse.de> wrote:
> 
> On Fri, 2 Dec 2022, Richard Biener wrote:
> 
>> On Thu, 1 Dec 2022, Siddhesh Poyarekar wrote:
>> 
>>> On 2022-12-01 11:42, Kees Cook wrote:
>>>> On Wed, Nov 30, 2022 at 02:25:56PM +0000, Qing Zhao wrote:
>>>>> '-Wstrict-flex-arrays'
>>>>>      Warn about inproper usages of flexible array members according to
>>>>>      the LEVEL of the 'strict_flex_array (LEVEL)' attribute attached to
>>>>>      the trailing array field of a structure if it's available,
>>>>>      otherwise according to the LEVEL of the option
>>>>>      '-fstrict-flex-arrays=LEVEL'.
>>>>> 
>>>>>      This option is effective only when LEVEL is bigger than 0.
>>>>>      Otherwise, it will be ignored with a warning.
>>>>> 
>>>>>      when LEVEL=1, warnings will be issued for a trailing array
>>>>>      reference of a structure that have 2 or more elements if the
>>>>>      trailing array is referenced as a flexible array member.
>>>>> 
>>>>>      when LEVEL=2, in addition to LEVEL=1, additional warnings will be
>>>>>      issued for a trailing one-element array reference of a structure if
>>>>>      the array is referenced as a flexible array member.
>>>>> 
>>>>>      when LEVEL=3, in addition to LEVEL=2, additional warnings will be
>>>>>      issued for a trailing zero-length array reference of a structure if
>>>>>      the array is referenced as a flexible array member.
>>>>> 
>>>>> At the same time, -Warray-bounds is updated:
>>>> 
>>>> Why is there both -Wstrict-flex-arrays and -Warray-bounds? I thought
>>>> only the latter was going to exist?
>> 
>> Sorry for appearantly not being clear - I was requesting 
>> -Wstrict-flex-arrays to be dropped and instead adjusting -Warray-bounds
>> to adhere to -fstrict-flex-arrays in both =1 and =2 where then =2
>> would only add the intermediate pointer results verification.
>> 
>> I think that's reasonable if documented since the default behavior
>> with -Wall will not change then unless the -fstrict-flex-arrays
>> default is altered.
> 
> Btw, your patch seems to implement the above plus adds 
> -Wstrict-flex-arrays.  It seems it could be split into two, doing
> the -Warray-bounds adjustment as first and the -Wstrict-flex-arrays 
> addition as second.

Yes, implementation should be very easy to be adjusted to drop the new -Wstrict-flex-arrays option.
But I still feel the new -Wstrict-flex-arrays option is good to add.

Qing
>  We do all seem to agree on the first so it's easy
> to go forward with that?
> 
> Thanks,
> Richard.