[llvm-dev] Using VMKit to convert Java Bytecode to LLVM IR

[Leslie Zhai via llvm-dev]

Hi all,

Thanks for discussing JVM topic!


在 2018年08月20日 23:32, Cranmer, Joshua via llvm-dev 写道:
>
> There’s been a lot of code changes from LLVM 3.3 to LLVM 6.0, so 
> expecting to just compile vmkit with a newer version of LLVM is not 
> going to work.
>
> Translation of pure JVM bytecode to LLVM itself is not particularly 
> challenging. You do need a garbage collector, which LLVM does not 
> provide, but that does not make the conversion that much harder. The 
> difficult part is that any effective project requires an 
> implementation of several Java classes that are very closely tied to 
> implementation details (particularly things like java.lang.Class or 
> java.lang.String). The most obvious source of the Java library 
> (OpenJDK) essentially requires you to implement the full and complex 
> dynamic class loading interfaces before you can even get a simple 
> hello world application running.
>
> VMKit did spend a lot of effort in being able to use the OpenJDK’s 
> implementation of the Java library, so while it may be a substantial 
> amount of effort to get VMKit to a newer version of LLVM (or OpenJDK, 
> for that matter), it is probably easier to do that instead of writing 
> your own JVM-to-LLVM converter.
>
What about Falcon[1] It is an optimizing Java JIT base on modern LLVM, 
perhaps it is able to learn from it. And I also have the same question: 
how to support JDK[2] library?

> *From:*llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of 
> *Ratnesh Tiwari via llvm-dev
> *Sent:* Monday, August 20, 2018 7:20
> *To:* llvm-dev <llvm-dev at lists.llvm.org>
> *Subject:* [llvm-dev] Using VMKit to convert Java Bytecode to LLVM IR
>
> Hi,
>
> I wanted to use VMKit  project to convert Java Bytecode to LLVM IR 
> bitcode. But  I do not know how to start, since I came to know that 
> VMkit is written for llvm -3.3 version, but I want it for latest LLVM 
> version 6.0.1.
>
I love Compiler Principle[3] so I migrated DragonEgg[4] from GCC-4.8 + 
LLVM-3.3 to GCC-8 + LLVM-6, you can also migrate VMkit from LLVM-3.3 to 
LLVM-8.

> So, could you please suggest me, whether I have to write it whole 
> project from scratch to meet my requirement of latest llvm version, or 
> can use existing project by building it. Since, I think existing VMKit 
> project which is unmaintained might have a lot of bug to meet latest 
> llvm version.
>
> Also tell me if I have to write it from scratch to convert from Java 
> Bytecode to LLVM IR, what is the basic code flow approach ,how to 
> start and related guidance. Please help me by suggesting above queries.
>
Java Bytecode to LLVM IR is not difficult, but there is 
graalvm/sulong[5] for transforming LLVM IR to Java Bytecode already :)

> Thanks & Regards
>
> Ratnesh Tiwari
>
>
>
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1. http://llvm.org/devmtg/2017-10/#talk12
2. http://hg.openjdk.java.net/jdk8u/jdk8u-dev/jdk/
3. https://www.leetcode.cn/2017/12/ilove-compiler-principle.html
4. http://lists.llvm.org/pipermail/llvm-dev/2017-August/116705.html
5. https://github.com/graalvm/sulong

-- 
Regards,
Leslie Zhai