Re: Question on -fwrapv and -fwrapv-pointer

[Richard Biener <richard.guenther@gmail.com>]

> Am 15.09.2023 um 17:25 schrieb Qing Zhao <qing.zhao@oracle.com>:
> 
> 
> 
>> On Sep 15, 2023, at 8:41 AM, Arsen Arsenović <arsen@aarsen.me> wrote:
>> 
>> 
>> Qing Zhao <qing.zhao@oracle.com> writes:
>> 
>>> Even though unsigned integer overflow is well defined, it might be
>>> unintentional, shall we warn user about this?
>> 
>> This would be better addressed by providing operators or functions that
>> do overflow checking in the language, so that they can be explicitly
>> used where overflow is unexpected.
> 
> Yes, that will be very helpful to prevent unexpected overflow in the program in general.
> However, this will mainly benefit new codes.
> 
> For the existing C codes, especially large applications, we still need to identify all the places 
> Where the overflow is unexpected, and fix them. 
> 
> One good example is linux kernel. 
> 
>> One could easily imagine a scenario
>> where overflow is not expected in some region of code but is in the
>> larger application.
> 
> Yes, that’s exactly the same situation Linux kernel faces now, the unexpected Overflow and 
> expected wrap-around are mixed together inside one module. 
> It’s hard to detect the unexpected overflow under such situation based on the current GCC. 

But that’s hardly GCCs fault nor can GCC fix that in any way.  Only the programmer can distinguish both cases.

Richard 

> Thanks.
> 
> Qing
>> -- 
>> Arsen Arsenović
>