[PATCH] libcsupport: Workaround for GCC 5.1 and later

Sebastian Huber sebastian.huber at embedded-brains.de
Wed Jul 15 06:50:03 UTC 2015

On 15/07/15 04:17, Chris Johns wrote:
> On 15/07/2015 8:15 am, Peter Dufault wrote:
>>> On Jul 13, 2015, at 20:01 , Chris Johns <chrisj at rtems.org> wrote:
>>> On 14/07/2015 4:20 am, Joel Sherrill wrote:
>>>> On 7/13/2015 1:06 PM, Sebastian Huber wrote:
>>>>> Yes, this option sounded like the right way to fix it, but...
>>>>> https://gcc.gnu.org/ml/gcc-help/2015-03/msg00093.html
>>>>> https://gcc.gnu.org/ml/gcc-help/2015-03/msg00094.html
>>>> Ouch! That is a big red flashing sign which says stay away!
>>>> And to Gedare's point of raising this as a PR, it is just
>>>> an optimization side-effect more than bug.
>>>> I wonder if this could impact any code in newlib? It should
>>>> have the same issue with the default calloc(). And maybe
>>>> some other routines like the string and mem* ones?
>>> For the record can someone please explain why 'calloc' broke with gcc 5
>>> on ARM in the first place ?
>>> What is the code construct in that specific function [1] that is causing
>>> the issue in the first place ? It seems a common type of idiom and I am
>>> sure it must exist in user code.
>> I’m guessing the optimizer is recognizing that the code sequence used to implement calloc() matches the definition for the built-in function calloc() and so changes it to a call to calloc().  That won’t be an issue in (most) user code.
> Agreed, so why is this not a bug in gcc ? Sebastian, is this logged with
> gcc ?

I didn't file a PR, only asked on the mailing list. My impression is 
that this is not a bug, but a feature that must be disabled by C library 

> If the code being optimized is the function 'calloc', which it should
> know, then maybe this is not such a good idea to call itself.

Yes, maybe this would complicate the compiler too much for a rare use 
case, e.g. C library.

Sebastian Huber, embedded brains GmbH

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