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From "Mikhail Loenko" <mloe...@gmail.com>
Subject Re: [drlvm][verifier] Dead-code and Java 6 verification issues
Date Wed, 07 Nov 2007 13:37:41 GMT
2007/11/7, Asaf Yaffe <asaf_yaffe@yahoo.com>:
> Hi Mikhail,
>
> You wrote:
>
> I like the idea of simplification which you pointed, but I think this
> approach is not quite correct in general: the dead code might be in
> the try block. In this case stackmap locals at the dead block should
> be assignable to stackmap at the handler_pc instruction.
>
> In other words, if catch block accesses locals defined before the try
>  block and
> this try block has a dead code, then stackmap for the dead code can't
> have empty locals: otherwise Java6 verification would fail
>
>
>
> I am not sure I understand the problem. Assume you "nop" all instructions in the dead
block and finalize it with an "athrow". According to the Java 6 verification rules, the only
thing you need is a [][java/lang/Throwable] StackMap. This is because (from the verification
algorithm):
>
> 1. A nop instruction is always type safe. The nop instruction does not affect the type
state
> 2. An athrow instruction is type safe iff the top of the operand stack matches Throwable
>
> The verifier cannot (and will not) check the consistency of this block with other blocks
because this block in unreachable.


> It will also not check the consistency of this block with "applicable" exception handlers
because it does not perform this check for "nop" and "athrow" instructions.

That's what I missed! Could you please provide a link to the quote in
the spec that nop and athrow are not checked against "applicable"
exception handlers?

Thanks,
Mikhail


>
> Thanks,
> Asaf
>
>
>
>
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