[Bug 272723] <sys/cdefs.h> header breaks restricted pointers in C++

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

--- Comment #1 from [email protected] ---
A commit in branch main references this bug:

URL:
https://cgit.FreeBSD.org/src/commit/?id=15876d9fd83fdfa7d541ea747eb40faeade975d2

commit 15876d9fd83fdfa7d541ea747eb40faeade975d2
Author:     Sebastian Huber <[email protected]>
AuthorDate: 2023-08-06 13:27:27 +0000
Commit:     Konstantin Belousov <[email protected]>
CommitDate: 2023-08-06 21:09:52 +0000

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

    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

 sys/sys/cdefs.h | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

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