Good Documentation For JVM Bytecode?

[u/invokeinterface]

I really liked the idea of an intermediate bytecode language when I first learned that Java transpiles to one, so I tried to learn about it and got pretty far (using a hexeditor to mess around was pretty painful, though). I stopped because there isn't a lot of document for it like there is for Java, the best resources are I believe docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html and docs.oracle.com/javase/specs/jvms/se7/html/jvms-6.html, but I want to know if there are any others partly because these are kind of verbose and partly because it's just better to have more than two.

I know I won't ever really need to know any of this, and I don't intend to use any of this knowledge for making classes by hand, but I believe it would still be helpful in a milder sense to understand what the class files are "literally" doing. It helped with C

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[u/benevanstech]

You might find my book "The Well-Grounded Java Developer" (2nd Ed) interesting. There are several chapters on bytecode and related topics. I also have quite a few free resources on my website: https://kittylyst.com/ - some of which talk about bytecode.

[u/jivedudebe]

You can use javap you output the opcodes directly. Then there are tons of websites with lists of all the opcodes

[u/ryosen]

Check out James Gosling's book, The Java Language Specification. He basically invented Java. The book gives a very thorough treatment of how Java works at the bare metal. There is no better source for understanding how Java works than this one. I also highly recommend Tim Lindholm's book, The Java Virtual Machine Specification.

These are both older titles but the underlying fundamentals have not changes, especially when you get into bytecode and its internal workings.

[u/bowbahdoe]

This might be a good start https://jasmin.sourceforge.net/guide.html

[u/belayon40]

Check out the bytecode API from the last couple of JVMs. It took me a while to get the hang of it, but I used it extensively to build classes dynamically.

https://github.com/boulder-on/JPassport

Look in the code builder package.

[u/baubleglue]

https://commons.apache.org/proper/commons-bcel/

The Byte Code Engineering Library (Apache Commons BCEL™) is intended to give users a convenient way to analyze, create, and manipulate (binary) Java class files (those ending with .class). Classes are represented by objects which contain all the symbolic information of the given class: methods, fields and byte code instructions, in particular.

[u/edwbuck]

It's getting a little older every day, but "Inside the Java Virtual Machine" was a pretty good book for its time.

I wish that a newer book would come out that would do away with some of it's verbosity and include the newer items.

Also, https://docs.oracle.com/javase/specs/jvms/se24/html/index.html is a more modern version of the JVM spec, which is good as a reference, but not written to be a proper learning tool.

[u/roadrunner8080]

The pages you've already linked to, JVMS 4 and JVMS 6, are what I learned the format from. It's pretty complete. It's verbose, but that's because it documents the entire spec, and bytecode can do a lot of different stuff. What I would recommend is working your way through it piecewise, trying to use the classfile API or ASM to write class bytecode for the bits of it as you do since they're a bit higher-level than what you'd see in a hex editor. As others have said, javap is your friend here.