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From "Mark Thomas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (BCEL-193) aastore instruction should not raise a verify error if an assignment compatiblity error is detected
Date Sat, 07 Mar 2015 18:08:38 GMT

    [ https://issues.apache.org/jira/browse/BCEL-193?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14351722#comment-14351722
] 

Mark Thomas commented on BCEL-193:
----------------------------------

I agree with Jérôme. Being too strict is just as much of a bug as not being strict enough.
I'll review the patch over the weekend with a view to getting it applied.

> aastore instruction should not raise a verify error if an assignment compatiblity error
is detected
> ---------------------------------------------------------------------------------------------------
>
>                 Key: BCEL-193
>                 URL: https://issues.apache.org/jira/browse/BCEL-193
>             Project: Commons BCEL
>          Issue Type: Bug
>          Components: Verifier
>    Affects Versions: 6.0
>            Reporter: Jérôme Leroux
>         Attachments: BCEL-193.patch, BCEL-193.zip
>
>
> The following valid code raises a verify error:
> {code:java}
> public class TestArrayAccess01 extends XTestArray01{
>     public static void test(){
>         XTestArray01[] array = new TestArrayAccess01[1];
>         array[0] = new XTestArray01();
>     }   
> }
> class XTestArray01 {}
> {code}
> The code above will throw an {{ArrayStoreException}} at runtime but the generated bytecode
is valid.
> _The Java Virtual Machine Specification Second Edition_ is ambigous about this kind of
issue. It states in §4.8.2 _Structural Constraints_ (http://docs.oracle.com/javase/specs/jvms/se5.0/html/ClassFile.doc.html#9308):
> {quote}
> The type of every value stored into an array of type reference by an aastore instruction
must be assignment compatible (§2.6.7) with the component type of the array.
> {quote}
> But in the {{aastore}} opcode description, there is no reference to any kind of linking
or verification error. The assignment compatiblity error is a runtime exception.
> In the _Java SE 7 Edition_ of __The Java Virtual Machine Specification_, the §4 has
been modified (http://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.9.2):
> {quote}
> The type of every value stored into an array by an aastore instruction must be a reference
type.
> The component type of the array being stored into by the aastore instruction must also
be a reference type. 
> {quote}
> The assignment compatibility check must not be done during the verification of the bytecode
but during its execution.



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