On Mon, 2012-03-26 at 10:11 +0200, Peter Zijlstra wrote:
> > However, note that today sparse doesn't evaluate anything in the
> > context, it doesn't even look at the first argument. So another thing
> > you can't really annotate well is things like this:
> >
> > struct foo_object *get_locked_object(...);
> >
> > This is why I used RETURN to give the return value a name, so you could
> > write
> > __acquires(&RETURN->lock)
>
>
> Right, but if it doesn't actually evaluate the expression used in the
> context this is going to be problematic.
It probably could -- but the question is what context to evaluate it in.
> > But I was also trying to make sparse actually evaluate the first
> > argument so it could tell the difference between two locks, which you
> > might not even care about ... (it would be nice though I think)
>
> Right, so what I thought we could maybe do is inject code in the
> callsites of these functions.
>
> So after the OP_CALL emit a piece of code that works like the
> __context__ stmt and can reference the return value that exists at that
> point.
>
> This also makes the conditional thing quite simple to do.
Indeed, but you'd need some sort of expression rewriting. Consider
void lock_obj(obj_t *o) __acquires(&o->lock);
void lock_obj(obj_t *obj)
{
__acquire(&obj->lock);
...
}
void foo(void)
{
...
lock_obj(&f);
...
unlock_obj(&f);
...
}
Now you suddenly need to replace "&o->lock" with "&(&f)->lock", when
checking the function itself it really is called "obj", not "o". Not
that sparse actually checks that the function behaviour matches the
declaration today though.
johannes
PS: Something else I had wanted to remind you of: the cond_lock thing
only works due to some sort of optimiser pass (is there such a thing?)
in sparse, sometimes it fails mysteriously because the condition isn't
the exact same condition or something.
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