[Mono-dev] [PATCH] Implement field load/store verification

Paolo Molaro lupus at ximian.com
Fri Jun 22 04:28:57 EDT 2007

On 06/21/07 Rodrigo Kumpera wrote:
> >This should be allowed in the .cctor for the class (same for the
> >equivalent case of an instance field and the .ctor): a test case is
> >something like:
> >
> >        readonly static MyValueType v = new MyValueType (5);
> >
> >Note, eventually you also need to add accessibility checks: the method
> >needs to be able to access the field keeping in mind both the field's
> >and the field's class visibility.
> >
> Definely, the spec say nothing about that, I'll add this check and mark it

There are references to this both in the instance constructor and type
initializers paragraphs (and also under Field contract attributes).

> as a spec issue. About the accessibility checks, I'm going to tackle all
> cases at once, as it should quite hairy, I believe.

There is code to deal with this in mini/mini.c, it is mostly complete
(look for can_access_field and can_access_method). Note that such code
must not be duplicated, we need to share it for both implementations.

> >The code for overlapped fields is not as trivial as this. It is moreover
> >something you should do on a per-type basis instead of per-field access
> >in the IL code. metadata/object.c has the code to do proper overlapping
> >field detection: that code should not be duplicated.
> I don't quite follow you, I should test it it's a load/store to a class with
> bad overlapping, even if the target is a good field?

The process of verification doesn't involve just a single method's
code: major things in the assembly containing it must be checked first.
verify.c contains quite a bit of those checks, more are needed of course.
Between them there is the field overlapping detection: it is a check
that doesn't belong inside the field access checks, but it belongs
to a per-type check that you need to perform anyway.
In the field access you need just to check if the type was ok
and the type should have been checked earlier (though it's reasonable to
check it lazily whenever a type is seen, but the full checks for the
type are needed, not just about overlapping fields). So you'd have code
like this whenever a type or class is seen:

	if (!type_is_ok (type)) {
		report verification/validation issues in type

and inside type_is_ok():
	// lazy check
	if (!type_has_been_checked (type))
		check_type (type);
	return type_status (type) == ok;

With this code field overlapping will just be one of the many checks
performed inside check_type ().


lupus at debian.org                                     debian/rules
lupus at ximian.com                             Monkeys do it better

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