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From: Bruno De Fraine <>
To: "" <>
Subject: newlib header breaks restricted pointers in C++
Date: Mon, 24 Jul 2023 22:23:26 +0000	[thread overview]
Message-ID: <> (raw)


As an extension, GCC and clang offer C99-style restricted pointers in C++ mode:

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
  #define	__restrict	restrict

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:

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

Bruno De Fraine

             reply	other threads:[~2023-07-24 22:23 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-24 22:23 Bruno De Fraine [this message]
2023-07-25 17:35 ` Corinna Vinschen
2023-07-25 17:46   ` Sebastian Huber
2023-07-25 18:48     ` Corinna Vinschen
2023-07-25 23:48       ` Steven J Abner
2023-07-27  9:00         ` Corinna Vinschen
2023-07-28 14:15           ` Sebastian Huber
2023-07-28 14:42             ` Joel Sherrill
2023-07-31 11:04       ` Bruno De Fraine

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