On Fri, Jul 06, 2007 at 12:29:27PM -0700, Josh Triplett wrote:
> The existing context annotations should suffice for many cases.
> compiler.h will need new wrappers for cases like requiring a lock. For
> a very simple example:
>
> compiler.h:
> #define require_context(x) __attribute__((context(x,1,1))
>
> magic_device.c:
> DEFINE_SPINLOCK(device_lock);
> struct the_device the_device require_context(device_lock);
*ugh*
More ugly syntax...
> compiler.h:
> #ifdef __CHECKER__
> #define fake_context(x) extern const int x
> #else
> #define fake_context(x)
> #endif
>
> preempt.h:
> fake_context(preemption);
> #define preempt_disable() ... __acquire(preemption)
> #define preempt_enable() ... __release(preemption)
> #define might_sleep_attr() ... /* something */
Still not expressive enough... Consider e.g.
struct foo *lookup_foo(char *s); // lookup by name, return NULL if failed
// or pointer to struct foo with ->mutex
// held. Caller should unlock.
It's legitimate, not particulary rare and AFAICS can't be expressed.
> Sparse does not yet enforce all of these conditions. Also, the "at
> least this value" semantic for the precondition makes it hard to use
> contexts for things like "this blocks" and "may not block in this
> context". As I said, it needs work. However, I intend for it to mean
> *exactly* the same thing on functions or variables, except that in the
> former case it means "when called", and in the latter case it means
> "when accessed". In both cases, you can require a context and change
> the context.
_What_ change in case of objects?
> A fine question. In the simple cases, "same symbol" will work fairly
> well; certainly better than the current "always equal" comparison. :)
> Ideally, however, you want "refers to the same value". Alias analysis
> could do a fairly good job of that, I think.
Not particulary useful, since for
int foo(struct bar *p) __acquires(&p->lock);
int bar(struct bar *p) __acquires(&p->lock);
you will get false negative in (n ? foo : bar) *and* it will persist even if
you go for
int foo(struct bar *p) __acquires(p);
int bar(struct bar *p) __acquires(p);
since you will have different symbols (same name, different scopes) here.
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