Re: [PATCH] add attribute none to pthread_setspecific (BZ #27714)

[Paul Eggert <eggert@cs.ucla.edu>]

[-- Attachment #1: Type: text/plain, Size: 714 bytes --]

On 4/23/21 8:24 AM, Martin Sebor wrote:
> 
> I think we considered variadic macros
> when we first introduced the attribute but rejected it for some
> reason that I'm not sure I remember.  Maybe because they're a C99
> feature and Glibc supports older compilers?

That shouldn't be an issue here, since the suggested change uses 
variadic macros for GCC 10 only.

Unless people were worried about running something like 'gcc -ansi' or 
'gcc -std=c89? To head that off at the pass, we can do the GCC 10 stuff 
only if !__STRICT_ANSI__. Also, while we're at it we should be 
C99-compatible in the variadic part (i.e., at least one named argument). 
Something like the attached (untested) patch, say.

[-- Attachment #2: cdefs-2.diff --]
[-- Type: text/x-patch, Size: 1368 bytes --]

diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index 8e244a77cf..b3b5456efd 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -586,15 +586,23 @@ _Static_assert (0, "IEEE 128-bits long double requires redirection on this platf
 # define __HAVE_GENERIC_SELECTION 0
 #endif
 
-#if __GNUC_PREREQ (10, 0)
 /* Designates a 1-based positional argument ref-index of pointer type
    that can be used to access size-index elements of the pointed-to
    array according to access mode, or at least one element when
    size-index is not provided:
      access (access-mode, <ref-index> [, <size-index>])  */
-#define __attr_access(x) __attribute__ ((__access__ x))
+#if __GNUC_PREREQ (11, 0)
+# define __attr_access(x) __attribute__ ((__access__ x))
+#elif __GNUC_PREREQ (10, 0) && !defined __STRICT_ANSI__
+# define __attr_access(x) __attr_access1 x
+# define __attr_access1(mode, ...) __attr_access##mode (mode, __VA_ARGS__)
+# define __attr_access__none__(mode, ...)
+# define __attr_access__read_only__(mode, ...) \
+    __attribute__ ((__access__ (mode, __VA_ARGS__)))
+# define __attr_access__read_write__ __attr_access__read_only__
+# define __attr_access__write_only__ __attr_access__read_only__
 #else
-#  define __attr_access(x)
+# define __attr_access(x)
 #endif
 
 /* Specify that a function such as setjmp or vfork may return