newlib header breaks restricted pointers in C++
Bruno De Fraine
Bruno.DeFraine@synopsys.com
Mon Jul 24 22:23:26 GMT 2023
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
This is a suggestion how the logic in the header could be rewritten:
/*
* We use `__restrict' as a way to define the `restrict' type qualifier
* without disturbing older software that is unaware of C99 keywords.
* GCC also provides `__restrict' as an extension to support C99-style
* restricted pointers in other language modes.
*/
#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901
#define __restrict restrict
#elif !__GNUC_PREREQ__(2, 95)
#define __restrict
#endif
Regards,
Bruno De Fraine
More information about the Newlib
mailing list