RFR: 8364360: Defining hidden class with no room in constant pool crashes the VM [v6]

[Coleen Phillimore]

On Fri, 31 Oct 2025 19:12:50 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> src/hotspot/share/classfile/classFileParser.cpp line 5529:
>> 
>>> 5527:     // Check for overflow.  cp_size is a u2.
>>> 5528:     assert(sizeof(cp_size) == sizeof(u2), "this overflow test depends on this");
>>> 5529:     guarantee_property(cp_size > _orig_cp_size, "Overflow in constant pool size for hidden class %s", CHECK);
>> 
>> Isn't this technically UB behavior? It isn't guaranteed that a u2 will overflow to a low value. It might be safer have cp_size be an int and then guarantee that cp_size < 65535.
>
> Doing a cast to u4 and an overflow check might be the best thing.  Then I won't need the assert.

I made this change and reran the VM jck tests.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27964#discussion_r2482474917