RE: [RFC][PATCH] rcu: Use typeof(p) instead of typeof(*p) *

[David Laight]

From: Mathieu Desnoyers
> Sent: 05 October 2021 16:15
> 
> ----- On Oct 5, 2021, at 9:47 AM, rostedt rostedt@xxxxxxxxxxx wrote:
> [...]
> > #define rcu_dereference_raw(p) \
> > ({ \
> > 	/* Dependency order vs. p above. */ \
> > 	typeof(p) ________p1 = READ_ONCE(p); \
> > -	((typeof(*p) __force __kernel *)(________p1)); \
> > +	((typeof(p) __force __kernel)(________p1)); \
> > })
> 
> AFAIU doing so removes validation that @p is indeed a pointer, so a user might mistakenly
> try to use rcu_dereference() on an integer, and get away with it. I'm not sure we want to
> loosen this check. I wonder if there might be another way to achieve the same check without
> requiring the structure to be declared, e.g. with __builtin_types_compatible_p ?

Could you pass the pointer to something like:
static __always_inline void foo(void *arg) {};

That would fail for integers.
Not sure whether CFI bleats about function pointers though.

	David

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