On Thu, 14 Oct 2010, Kees Cook wrote:
> I've got a situation where I want to check 2 things before a 3rd thing, but
> the order of the first 2 don't matter. What's the best way to do this?
>
> Currently, I have two rules, but with the get_ and PAGE_SIZE tests swapped
> between them:
>
> @cfu_page1@
> position cfu.p;
> expression f, s, I, E1, E2, E3;
> type T;
> @@
>
> I =
> (
> (T)get_zeroed_page(...)
> |
> (T)__get_free_page(...)
> )
> ... when != I = E1
> (
> if ( s != PAGE_SIZE || ... ) { ... return ...; }
> |
> if ( s > PAGE_SIZE || ... ) { ... return ...; }
> )
> ... when != s = E2
> when != I = E3
> copy_from_u...@p(I, f, s)
>
> Instead of the two rules, is there some way to simplify this?
We were originally planning to support a ooo operator that would go
between two things that should appear in any order, but never got around
to it. If you really want to match A ... B ... C and B ... A ... C, ie
with A and B in the same control-flow path, then I think that two rules is
the simplest. If you just want A and B to appear somewhere before C, but
not necessarily in the same control-flow path, you could do something with
positions and depends on. That would require four rules: 1) match
C and establish a position variable, 2) exists match A ... C, 3)
exists match B ... C, 4) only consider uses of C whose position satisfied
both 2 and 3.
julia
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