[gcc r12-8007] Document that the 'access' and 'nonnull' attributes are independent

[gcc r12-8007] Document that the 'access' and 'nonnull' attributes are independent

[David Malcolm]

https://gcc.gnu.org/g:0b5723d74f3a731380f78dc1a02a2376951388cf

commit r12-8007-g0b5723d74f3a731380f78dc1a02a2376951388cf
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Tue Apr 5 16:43:16 2022 -0400

    Document that the 'access' and 'nonnull' attributes are independent
    
    gcc/ChangeLog:
            * doc/extend.texi (Common Function Attributes): Document that
            'access' does not imply 'nonnull'.
    
    Signed-off-by: David Malcolm <dmalcolm@redhat.com>

Diff:
---
 gcc/doc/extend.texi | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 8381eb620ea..e10b10bc1f1 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -2652,6 +2652,14 @@ The mode is intended to be used as a means to help validate the expected
 object size, for example in functions that call @code{__builtin_object_size}.
 @xref{Object Size Checking}.
 
+Note that the @code{access} attribute merely specifies how an object
+referenced by the pointer argument can be accessed; it does not imply that
+an access @strong{will} happen.  Also, the @code{access} attribute does not
+imply the attribute @code{nonnull}; it may be appropriate to add both attributes
+at the declaration of a function that unconditionally manipulates a buffer via
+a pointer argument.  See the @code{nonnull} attribute for more information and
+caveats.
+
 @item alias ("@var{target}")
 @cindex @code{alias} function attribute
 The @code{alias} attribute causes the declaration to be emitted as an alias