StackMap problem

[Adam Sotona]

Hi Mark,
Both attached class listings are missing stack map frames at branch targets, and they seem to be invalid.
I would like to ask what compiler generates the first class and how your tool adds the instrumentation code.
My first impression is that I don’t see any trace of Class-File API stack map generator involment. Transformation of a method with missing or invalid stack map would generate new stack maps, unless explicitly disabled.

Thanks,
Adam


From: classfile-api-dev <classfile-api-dev-retn at openjdk.org> on behalf of Mark Roberts <markro at cs.washington.edu>
Date: Tuesday, 28 January 2025 at 21:45
To: classfile-api-dev at openjdk.org <classfile-api-dev at openjdk.org>
Cc: Chen Liang <chen.l.liang at oracle.com>
Subject: StackMap problem
The existence of compiler generated, unnamed local temps (no LocalVariable code element) seems to cause a problem with stack maps.

The ‘source’ attachment shows the problem method.   The ‘before’ attachment shows the generated code before instrumentation.  Note that the compiler generates an unnamed temp at slot 0 to store the exception code. The stackmap for the branch target says same locals, which is correct.

The ‘after’ attachment shows the code generated after our tool has added instrumentation code – note the addition of a new local variable at slot 1.  The stackmap for the branch target still says same locals, which is no longer correct. This causes the iload_1 @41 to fail.

I tried to see if this issue has already been reported, but I was unable to figure out how to search https://bugs.java.com/bugdatabase/ by keyword.

Mark



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