DWARF Standard


220513.1 David Lloyd No way to represent Java bytecode index in source information Enhancement Open Jini Susan George

Section 6.2.2, pg 150

A little background: When the Java portions of the DWARF standard 
were added, the compiled Java landscape was very different. In the 
past couple of years, so-called "native Java" or "static image Java" 
has seen a surge in popularity using various new approaches. Most 
prominently of these, the "native image" tool which is shipped as 
a part of Oracle's GraalVM is seeing a fairly significant increase 
in real-world deployment. As such we've been evaluating approaches 
to easing the debug experience for these binary Java deployments.

Now, to the point: Java relies on more information that just the 
line number when debugging. Java is normally compiled from source 
to bytecode; the native image tools then compile the bytecode to 
a native machine executable. The bytecode index of any given 
instruction is significant to Java debuggers and to the process 
of debugging Java in general.

So, what is requested is the addition of another optional state 
machine register (6.2.2) which tracks the bytecode index corresponding 
to the current instruction. This would be largely similar to how 
line and column numbers are tracked. Bytecode indices in Java are 
16-bit unsigned values.

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