HotSpot and IBM's J9 behave a little different when verifying this class

[Michael Rasmussen]

On 14 April 2017 at 02:15, Yuting Chen <chenyt.cs.sjtu at gmail.com> wrote:
> Thanks, Remi and Michael.
>
> The difference appears only when all of the paths end in athrow. Then
> what does the comment ("Return TRUE if all code paths starting with
> start_bc_offset end in bytecode athrow or loop") in verifier.cpp mean?
> It seems that J9 follows this comment.
>
> Both verifiers can decline the class if "athrow" is changed to "return".

Yes, for constructors, if exit is via return, then there cannot be any
uninitializedThis, but allowed if exit is via athrow.

But, your problem is, that your two frame aren't assignable to each other.
>>> Current Frame:
>>>    bci: @1
>>>    flags: { flagThisUninit }
>>>    locals: { uninitializedThis, integer, integer }
>>>    stack: { integer }
>>>  Stackmap Frame:
>>>    bci: @11
>>>    flags: { }
>>>    locals: { top, integer, integer }
>>>    stack: { }

While the locals are compatible, the flags are not, you cannot go from
{ flagThisUninit } to {}
http://hg.openjdk.java.net/jdk8u/jdk8u/hotspot/file/tip/src/share/vm/classfile/stackMapFrame.cpp#l190

/Michael