Checking for 'Stack size mismatch'

[Øystein Myhre Andersen]

Thanks for the tip!

On Mon, Mar 18, 2024 at 9:22 AM Adam Sotona <adam.sotona at oracle.com> wrote:

> Hi,
>
> You are suggesting very specific operations with significant performance
> effects to be applied for all ClassFile API use cases.
>
> Instead of wiring a specific code inside all the code building I suggest
> you to look at java.lang.classfile.components.CodeStackTracker
> <https://download.java.net/java/early_access/jdk22/docs/api/java.base/java/lang/classfile/components/CodeStackTracker.html>
> for inspiration.
>
> This way you can (conditionally) plug any custom transformation into your
> code building. For example a transformation that would print out a debug
> output you asked in another thread, or you may track origin of labels,
> verify actual stack content, print out any additional info, all optional
> and without affecting the core performance.
>
>
>
> Adam
>
>
>
> *From: *classfile-api-dev <classfile-api-dev-retn at openjdk.org> on behalf
> of Øystein Myhre Andersen <o.myhre at gmail.com>
> *Date: *Sunday, March 10, 2024 at 16:04
> *To: *liangchenblue at gmail.com <liangchenblue at gmail.com>
> *Cc: *classfile-api-dev at openjdk.org <classfile-api-dev at openjdk.org>
> *Subject: *Re: Checking for 'Stack size mismatch'
>
> Sorry again: Now I mess up: it's possible like this:
>
>  - At labelBinding what is in the  'come-from' list  is checked
>  - With a later backward jump to this label, it is checked again
>
>
>
> On Sun, Mar 10, 2024 at 3:54 PM Øystein Myhre Andersen <o.myhre at gmail.com>
> wrote:
>
> Sorry: This does not handle backward jumps.
>
>
>
> But   a 'come-from' list  might be useful for the StackMapGenerator.
>
> And, maybe speed it up.
>
>
>
> P.S. In the byte code of Simula, we had the rule that a label only had one
> and only one associated goto.
>
>
>
> On Sun, Mar 10, 2024 at 3:21 PM Øystein Myhre Andersen <o.myhre at gmail.com>
> wrote:
>
>
> 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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