24-28 August 2020
US/Pacific timezone

Lightning Talk: Teaching GraalVM DWARFish : Debugging Native Java using gdb

24 Aug 2020, 08:15
10m
GNU Tools track/Virtual-Room (LPC 2020)

GNU Tools track/Virtual-Room

LPC 2020

150
GNU Tools Track GNU Tools Track

Speaker

Andrew Dinn (Red hat)

Description

Or is it DWARVish? Whatever, GraalVM Native implements compilation of a
complete suite of Java application classes to a single, complete, native
ELF image. It's much like how a C/C++ program gets compiled. Well,
except that the image contains nothing to explain how the bits were
derived from source types and methods or where those elements were
defined. Oh and the generated code is heavily inlined and optimized
(think gcc -O2/3). Plus many JDK runtime classes and methods get
substituted with lightweight replacements. So, a debugging nightmare.

Anyway, we have resolved the debug problem much like how you do with
C/C++ by generating DWARF records to accompany and explain the program
bits. So far, we have file and line number resolution, breakpoints,
single stepping & stack backtraces. We're now working on type names and
layouts and type, location & liveness info for heap-mapped
values/objects, parameters and local vars. I'll explain how we obtain
the necessary input from the Java compiler, how we model it as DWARF
records and how we test it for correctness using objdump and gdb itself.
By that point I will probably need to stop to take a breath

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Primary author

Andrew Dinn (Red hat)

Presentation Materials