On 11/01/2019 11:11 pm, Remi Forax wrote:
----- Mail original -----
De: "David Holmes" <david.hol...@oracle.com>
À: "Adam Farley8" <adam.far...@uk.ibm.com>, "core-libs-dev"
<core-libs-dev@openjdk.java.net>
Envoyé: Vendredi 11 Janvier 2019 14:02:06
Objet: Re: RFR: JDK-8216558: Lookup.unreflectSetter(Field) fails to throw
IllegalAccessException for final fields
On 11/01/2019 10:46 pm, Adam Farley8 wrote:
Hi All,
I posit that you shouldn't be able to change the contents of a a final
field.
Nice in theory, but not true in practice.
However, if you use Field.setAccessible(true) before calling
Lookup.unreflectSetter(Field), then you can get a MethodHandle that allows
you to set the (reflected) value of a static final field.
This seems wrong to me, so here's a change to fix it.
See:
https://docs.oracle.com/javase/10/docs/api/java/lang/reflect/Field.html#set(java.lang.Object,java.lang.Object)
"If the underlying field is final, the method throws an
IllegalAccessException unless setAccessible(true) has succeeded for this
Field object and the field is non-static. Setting a final field in this
way is meaningful only during deserialization or reconstruction of
instances of classes with blank final fields, before they are made
available for access by other parts of a program. Use in any other
context may have unpredictable effects, including cases in which other
parts of a program continue to use the original value of this field. "
the same semantics are supported by MH/VH.
No VH doesn't support setAccessible (don't ask me why) ...
I must correct myself. Of course MH and VH should not support
setAccessible. MH and VH represent bytecode semantics and bytecode knows
nothing about setAccessible.
That said bytecode semantics for final fields are tricky if strictly
followed, as we should allow MH/VH to set a final field if called from
the <clinit>/<init> of the target class - as that is what
putfield/putstatic would do.
David
-----
But note this requires the field to be non-static - if you can set a
static final field this way then that may be a bug (they can still be
set via native methods of course).
David
Rémi
-----
webrev: http://cr.openjdk.java.net/~afarley/8216558/webrev/
bug: https://bugs.openjdk.java.net/browse/JDK-8216558
Opinions invited.
Best Regards
Adam Farley
IBM Runtimes
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