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

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

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On 4/22/21 2:30 PM, Martin Sebor via Libc-alpha wrote:

> -	__THROW;
> +	__THROW __attr_access_none (2);

Instead of inventing a new __attr_access_none macro that developers will 
need to remember, why not add support to the existing __attr_access 
macro? That is, uses can look like this:

      __THROW __attr_access ((__none__, 2));

if we define __attr_access with something like the attached patch.

Alternatively, one could keep both cdefs.h and the callers simple by 
doing access attribute checking only for GCC 11 and later. That'd be 
good enough in the long run.

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diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index 8e244a77cf..db3283ec7f 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -586,15 +586,26 @@ _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)
+# define __attr_access(x) __attr_access1 x
+# define __attr_access1(access_mode, ...) \
+    __attr_access##access_mode (__VA_ARGS__)
+# define __attr_access__none__(...)
+# define __attr_access__read_only__(...) \
+    __attribute__ ((__access__ (__read_only__, __VA_ARGS__)
+# define __attr_access__read_write__(...) \
+    __attribute__ ((__access__ (__read_write__, __VA_ARGS__)
+# define __attr_access__write_only__(...) \
+    __attribute__ ((__access__ (__write_only__, __VA_ARGS__)
 #else
-#  define __attr_access(x)
+# define __attr_access(x)
 #endif
 
 /* Specify that a function such as setjmp or vfork may return