On Wed, 2022-03-23 at 17:52 +0100, Sebastian Huber wrote:
> On 23/03/2022 17:31, Martin Sebor via Gcc-patches wrote:
> >
> > The concern is that the constraints implied by atttributes access
> > and
> > nonnull are independent of each other. I would suggest to document
> > that without talking about dereferencing because that's not implied
> > by either of them. E.g., something like this (feel free to tweak
> > it
> > as you see fit):
> >
> > Note that the @code{access} attribute doesn't imply the same
> > constraint as attribute @code{nonnull} (@pxref{Attribute
> > nonnull}).
> > The latter attribute should be used to annotate arguments that
> > must
> > never be null, regardless of the value of the size argument.
>
> I would not give an advice on using the nonnull attribute here. This
> attribute could have pretty dangerous effects in the function
> definition
> (removal of null pointer checks).
>
That's a fair point.
Here's a v3 of the patch, which tones down the advice, and mentions that
there are caveats when directing the reader to the "nonnull" attribute.
How does this look?
gcc/ChangeLog:
* doc/extend.texi (Common Function Attributes): Document that
'access' does not imply 'nonnull'.
Signed-off-by: David Malcolm <dmalc...@redhat.com>
---
gcc/doc/extend.texi | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index a4a25e86928..539dad7001d 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
--
2.26.3
