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sys/cdefs.h: fix for use __restrict in C++

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Newlib shares large parts of <sys/cdefs.h> with FreeBSD and received
this bug report:

https://sourceware.org/pipermail/newlib/2023/020400.html

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

Rewrite the logic in the header so that __restrict is kept alone when
available.

PR:	272723
MFC after:	1 week
This commit is contained in:
Sebastian Huber 2023-08-06 16:27:27 +03:00 committed by Konstantin Belousov
parent 9ec7a595ed
commit 15876d9fd8
1 changed files with 7 additions and 9 deletions
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16
sys/sys/cdefs.h
View file

@ -403,17 +403,15 @@
#endif
/*
* 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.
* 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 !(__GNUC__ == 2 && __GNUC_MINOR__ == 95)
#if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 199901
#define __restrict
#else
#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901
#define __restrict restrict
#endif
#elif !__GNUC_PREREQ__(2, 95)
#define __restrict
#endif
/*