[cfe-dev] Ownership attribute for malloc etc. checking

[Jeffrey Yasskin]

I'm not any sort of authority on the checker, so take this with a
grain of salt, but I had a comment on the syntax here.

Identifying a function argument by index is really error prone and
hard to use. In particular, you wind up having to tell people to use
different bases for member functions vs non-member functions, and fix
up the index when anything changes. It would be much nicer to attach
the attribute to the actual argument, like

void bar(char * it __attribute((ownership_takes(malloc)))) {
  free(it);
}

I don't know whether this placement is possible with clang's current
parser—gcc doesn't allow it—but I believe Sean's working on fixing
that over the summer.

On Wed, Jun 23, 2010 at 7:12 PM, Andrew McGregor <andrewmcgr at gmail.com> wrote:
> This is a second try at some attributes that presently only enable the
> malloc checker to be smarter.  Syntactically, however, the attributes are
> intended to be more generally useful.
> The attributes are currently used like this:
> void __attribute((ownership_takes(malloc, 1))) bar(char * it) {
>   free(it);
> }
> char * __attribute((ownership_returns(malloc, 1))) bar2(size_t i) {
>   return (char *) malloc(i);
> }
> There is a third called ownership_holds.  The distinction is that
> ownership_takes does not allow the resource to be used after passing it in,
> while ownership_holds does.
> The first argument is intended to be the name of a type of resource, in this
> case memory allocated through malloc.  This is the only value currently
> checked, any other value is silently ignored.
> The second argument is an index into the function's argument list, for
> ownership_returns it is the size of the malloc region, for the others it is
> the pointer to check.
> In this patch, only one argument per function can be annotated, that still
> has to be fixed.
> Andrew
>
>
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