On 20/04/2017 12:42 PM, John Rose wrote:
On Apr 18, 2017, at 11:42 AM, Dan Smith <[email protected]
<mailto:[email protected]>> wrote:
I've uploaded a draft of JVMS changes for JEP 181 "Align JVM Checks
with Java Language Rules for Nested Classes" to:
http://cr.openjdk.java.net/~dlsmith/private-access.html
classHasValidNest(Class) :-
classMemberOfNestName(Class, HostName),
classDefiningLoader(Class, L1),
loadedClass(HostName, L1, HostClass),
samePackageName(Class, HostClass),
classClassName(Class, Name),
classNestMemberNames(HostClass, MemberNames),
member(Name, MemberNames),
classDefiningLoader(HostClass, L2),
loadedClass(Name, L2, Class).
In English:
When validating nestmate attributes, if a class C with name
"C" has an attribute MemberOfNest("H"), it is valid only if the
following are all true:
1. The string "H" resolves from C's loader (L1) as H.
2. The strings "C" and "H" have the same package prefix.
3. H contains an attribute of the form NestMembers(…"C"…).
4. The string "C" resolves from H's loader (L2) as C.
Steps 1 and 4 are both CONSTANT_Class resolution operations.
Step 3 is a simple search of a symbol list, which is easy.
This logic can be simplified by testing that C and H must
be in the same runtime package. In that case, L1 and L2 are
identical, and step 4 becomes:
4'. C and H have the same defining loader.
Then we can refactor 2 and 4' into a more direct check on
runtime package (using the functor 'sameRuntimePackage'):
1. The string "H" resolves from C's loader (L1) as H.
2'. C and H have the same runtime package.
3. H contains an attribute of the form NestMembers({... "C", ...}).
This is a simpler specification, and it also closes any possible
loopholes in package/nest alignment by insisting on equal
runtime packages from the start.
It also avoids a possibly wasteful class loading step, which
is only necessary if we allow L1 and L2 to differ. That would
be a pathology IMO, not a use case.
The way I visualize this is that each newly arrived class
checks in with its host. If the name is on the list, it gets in.
Sound good?
This is basically what the existing validation logic does - modulo the
order of operations:
1. load "H" using C's classloader
2. H contains an attribute of the form NestMembers({... "C", ...})
3. Check is_same_package(C, H)
The order can be changed if that is significant.
David
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— John
