Re: [PATCH v2] newlib: fix build with <gcc-5 versions

[Jordi Sanfeliu <jordi@fibranet.cat>]

For what it’s worth, I'm using GCC 4.x in my humble hobby OS (fiwix.org) 
focused on old i386 machines. So for me, will be fine to continue be 
able to build Newlib with GCC 4.x.

Also, I noticed that GCC 4.x needs less memory footprint than GCC 5.x, 
so it makes it more appreciated in old machines.

Thanks.



On 3/20/22 02:21, Mike Frysinger wrote:
> On 17 Mar 2022 10:49, Corinna Vinschen wrote:
>> On Mar 16 22:41, Mike Frysinger wrote:
>>> On 16 Mar 2022 10:17, R. Diez wrote:
>>>>>> Therefore, compiling your code with GCC < 5 will silently break your application.
>>>>>> After all, the only reason to use __builtin_mul_overflow() is
>>>>>> that you need to check for overflow, is it?
>>>>>
>>>>> practically speaking, i don't think this is a big deal.  newlib gained these
>>>>> checks only "recently" (<2 years ago).  newlib has been around for much much
>>>>> longer, and the world didn't notice.
>>>>
>>>> Such general justifications wouldn't pass quality assurance (if we had one).
>>>
>>> in your opinion.  software is not perfect, it's trade-offs.
>>>
>>>>> yes, if an app starts trying to allocate
>>>>> huge amounts of memory such that it triggers 32-bit overflows when calculating,
>>>>> the new size, it will probably internally allocate fewer bytes than requested,
>>>>> and things will get corrupted.  but like, don't do that :p.  such applications
>>>>> probably will have other problems already.
>>>>
>>>> You are suggesting that this only affects memory allocation, but the patch is for libc/include/sys/cdefs.h , so those mine traps will be available for everybody.
>>>>
>>>> People will tend to assume that anything in Newlib is correct, and code has a way to get copied around and re-used.
>>>>
>>>> There are many ways to mitigate the risk:
>>>>
>>>> - Require GCC 5.
>>>> - Provide a proper implementation of __builtin_mul_overflow().
>>>> - Patch all users of __builtin_mul_overflow() within Newlib, so that they do not use it if the compiler does not provide it.
>>>> - Issue a compilation warning for GCC < 5 that the "stub" __builtin_mul_overflow() is broken.
>>>>     Note that this is not actually a "stub" implementation in the common sense.
>>>> - Add an "assert( false ) // fix me" inside the implementation.
>>>> - Add a comment stating that the "stub" implementation is not actually correct.
>>>
>>> any option that prevents correct execution with gcc-4 is not an improvement.
>>> if you care this much, feel free to contribute a patch.  or use gcc-5+ and
>>> not worry about it.
>>> -mike
>>
>> Does anybody actually care for building with gcc < 5?  If not, we
>> should just make gcc 5 a prerequisite.
> 
> i'm using gcc 4.9 for one of my targets which is why i noticed :).
> -mike

-- 
Jordi Sanfeliu
FIBRANET Network Services Provider
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