Checking for 'Stack size mismatch'

[Øystein Myhre Andersen]

Yes, I know which method builder is called.
I have a class file builder like:

byte[] bytes = ClassFile.of().build(currentClassDesc(),
      classBuilder -> {
            classBuilder
                  ....
                  .withMethodBody("_STM", MTD_STM, ClassFile.ACC_PUBLIC,
                        codeBuilder -> buildMethod_STM(codeBuilder));
      }
);

Within 'buildMethod_STM' I traverse a syntax tree building code from each
node.
Somewhere there a mistake is made that leads to 'stack size mismatch'.

When I return from 'buildMethod_STM', the method builder will finalize its
work.
It generates the bytecode and builds the stack map table.
I assume that it checks the stack size at all labels, it must do so to
build a correct stack map table.

Along with the error message comes a complete dump of the entire method.

Checking for 'Stack size mismatch' is currently done in
'java.base/jdk.internal.classfile.impl.StackMapGenerator'.
It would have been nice if this was tested earlier by Codebuilder when the
labelBinding pseudo instruction was created.

One way it might be done is to build a 'come-from' list within labelBinding
pseudo instruction.

On Sat, Mar 9, 2024 at 10:10 PM - <liangchenblue at gmail.com> wrote:

> What are you trying to do? So you are writing a class and there's a stack
> size error, but you don't know which method builder this stack size error
> is from?
>
> On Sat, Mar 9, 2024 at 2:04 PM Øystein Myhre Andersen <o.myhre at gmail.com>
> wrote:
>
>> You said:  as this error can only be detected at run time.
>> That is wrong. It occurs when building stack-map.
>>
>> On Sat, Mar 9, 2024 at 7:38 PM - <liangchenblue at gmail.com> wrote:
>>
>>> Hi Øystein,
>>> ClassFile API does not always ensure the created bytecode is valid, and
>>> allowing creation of code with invalid stack size is a feature instead of a
>>> bug. A stack size mismatch problem, in essence, is closer to the error
>>> which a user forgot to call a builder method. And putting this check
>>> earlier doesn't really help, as this error can only be detected at run
>>> time. You can always use ClassFile.verify to verify your generated class
>>> files.
>>>
>>> In addition, CodeBuilder supports chaining; if we add the size checking
>>> in each item of the chain, it will introduce a performance penalty.
>>>
>>> Chen
>>>
>>> On Sat, Mar 9, 2024 at 8:42 AM Øystein Myhre Andersen <o.myhre at gmail.com>
>>> wrote:
>>>
>>>> Checking for 'Stack size mismatch' is currently done in 'java.base/jdk.internal.classfile.impl.StackMapGenerator'.
>>>> It would have been nice if this was tested earlier by Codebuilder when the instructions was created.
>>>>
>>>> For example, by keeping track of the stack size curing code building.
>>>>
>>>> It is good programming practice to catch errors as early as possible.
>>>>
>>>>
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