RFR(S) 8046233: VerifyError on backward branch

[David Holmes]

Thanks for clarifying this Harold.

David

On 25/06/2014 7:24 AM, harold seigel wrote:
> Hi David,
>
> Thanks for the review.
>
> My explanation of this bug fix is misleading.
>
> The appropriate text, shown here, was removed from JVMS 8 because it was
> deemed unnecessary.  See JDK-6594979
> <https://bugs.openjdk.java.net/browse/JDK-6594979>.
>
>     A valid instruction sequence must not have an uninitialized object
>     on the operand stack or in a local variable at the target of a
>     backwards branch if the special type of the uninitialized object is
>     merged with a special type other than itself, or in a local variable
>     in code protected by an exception handler or a |finally| clause.
>     Otherwise, a devious piece of code might fool the verifier into
>     thinking it had initialized a class instance when it had, in fact,
>     initialized a class instance created in a previous pass through a loop.
>
> The text is unnecessary because the existing stack merging code in the
> verifier should already detect if the special type of the uninitialized
> object is being merged with a special type other than itself.
>
> The verifier code is being changed because it is incorrect for both JVMS
> 7 and JVMS 8.  It is throwing a VerifyError for any backward branch
> whose target contains an uninitialized object, even if the special types
> of the uninitialized objects being merged are the same.
>
> I need to add an additional test for this fix, one that attempts to
> merge two stacks containing two different uninitialized special types.
>
> In general, I think that the verification rules depend on the version of
> the classfile being verified, but I don't think that is an issue for
> this fix.  The verifier is wrong in both cases.
>
> Thanks, Harold
>
>
> On 6/23/2014 10:33 PM, David Holmes wrote:
>> Hi Harold,
>>
>> Are the verification rules dependent on the VM or the version of the
>> classfile being verified?
>>
>> Thanks,
>> David
>>
>> On 24/06/2014 6:42 AM, harold seigel wrote:
>>> Hi,
>>>
>>> Please review this small fix for bug 8046233.  The fix removes the
>>> verifier check concerning backward branches and uninitialized objects
>>> because, as discussed in the bug report, the requirement has been
>>> removed from JVM Specification 8.
>>>
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8046233
>>> Open webrev: http://cr.openjdk.java.net/~hseigel/bug_8046233/
>>>
>>> The fix was tested with the JCK lang and vm tests, the default method
>>> tests, the UTE verifier and quick tests, the JTREG hotspot tests, and a
>>> test that reproduced the problem.
>>>
>>> Thanks, Harold
>