newlib header breaks restricted pointers in C++

[Sebastian Huber]

On 25.07.23 19:35, Corinna Vinschen wrote:
> Hi Bruno,
> 
> On Jul 24 22:23, Bruno De Fraine wrote:
>> Hello,
>>
>> As an extension, GCC and clang offer C99-style restricted pointers in C++ mode:
>> https://gcc.gnu.org/onlinedocs/gcc/Restricted-Pointers.html
>>
>> We notice that this extension is broken when including newlib headers: restricted pointers are treated as ordinary pointers.
>>
>> We traced this to the following section of newlib/libc/include/sys/cdefs.h:
>>
>>    /*
>>     * GCC 2.95 provides `__restrict' as an extension to C90 to support the
>>     * C99-specific `restrict' type qualifier.  We happen to use `__restrict' as
>>     * a way to define the `restrict' type qualifier without disturbing older
>>     * software that is unaware of C99 keywords.
>>     */
>>    #if !(__GNUC__ == 2 && __GNUC_MINOR__ == 95)
>>    #if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 199901
>>    #define	__restrict
>>    #else
>>    #define	__restrict	restrict
>>    #endif
>>    #endif
>>
>> While the GCC __restrict extension was indeed introduced in GCC 2.95, it is not limited to this version; the extension is also not limited to C90:
>> https://gcc.gnu.org/gcc-2.95/c++features.html
> Either way, the above has been taken from FreeBSD, and it is still,
> as of today, the same expression as used in FreeBSDs sys/cdefs.h
> file.
> 
> Seb, any input on this?

I added a FreeBSD bug report:

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=272723

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