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I have written a JVM in Rust

andreabergia.com

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Re: I have written a JVM in Rust

#121

Post by grishka »

mshockwave wrote: post #80
ChuckMcM wrote: post #78

That is pretty awesome! When I joined the Java effort in '92 (called Oak at the time) the group I was with was looking at writing a full OS in Java. The idea being that you could get to just the minimal set of things needed as "machine code" (aka native methods) you could reduce the attack surface of an embedded OS. (originally Java was targeted to run in things like TV's and other appliances). We were, of course, wo…

> writing a full OS in Java IMAO, Android kind of achieve that...kind of. They write lots of OS logics in Java (or Kotlin) but mixing lots of system services written in native code at the same time, interconnected by the famous (or infamous?) Bind IPC.

Android isn't conventional Java. For starters, its runtime uses its own bytecode (dex) that's based on registers instead of a stack. But then, also, many things that aren't related to GUI are C++ with a thin Java wrapper on top.

When I think about a "Java OS", I imagine a JVM running in kernel mode, providing minimal OS functionality (scheduler, access to hardware I/O ports) and there not being any kind of userspace.

Re: I have written a JVM in Rust

#122

Post by skitter »

celeritascelery wrote: post #99
andreabergia wrote: post #91

Earlier quoted context omitted.

I wanted to express the fact that everything that gets allocated (call stack, frames, classes, and objects) is alive and valid until the "root" VM is, thus I used 'a more or less everywhere. I also struggled with a got a ton of errors from the borrow checker initially, and I fixed many of those with a lot of explicit lifetimes, but it's not impossible that in some places they are unnecessary.

> I wanted to express the fact that everything that gets allocated (call stack, frames, classes, and objects) is alive and valid until the "root" VM is, thus I used 'a more or less everywhere. That's not being expressed in the type system. The lifetime 'a is unbounded (meaning you can make it anything you want, including 'static) so anything that shares 'a can outlive the vm without rust complaining. it would be no d…

Funnily enough I did the same in an early wip version of my toy JVM. Ended up using unsafe to use 'static references internally but only hand out wrappers that include a reference to the JVM. This also ensures that objects/classes/… from one JVM can't be used in another one.

Re: I have written a JVM in Rust

#123

Post by ywei3410 »

whizzter wrote: post #15
xxs wrote: post #4

Earlier quoted context omitted.

pretty much this - generics have (rare) implications to the reflection (but it's unsupported as well) but overall they are replaced with the nearest class/interface when compiled. OTOH lack of string interning is super strange [it's trivial to implement], and w/o it JVM is not a thing. String being equal by reference is important, and part of JLS. Lack of thread makes the entire endeavor a toy project.

Not entirely correct, last I checked string interning was ONLY guaranteed for those strings defined in source and read in during class loading, strings created via the String constructor (f.ex. via StringBuilder) CAN duplicate those strings that you hardcoded in your sources, to get the "canonical" string in those cases you have to invoke String.intern() if memory serves me correct. https://docs.oracle.com/en/java/ja…

There's also the new JVM option which eludes me at the moment which sweeps the strings which are promoted to the older generation and interns them.

Not certain about whether `String.intern` is permanently stored; I rather suspect that it sweeps the existing strings since iirc the java string has a hash associated with it anyway.

Re: I have written a JVM in Rust

#124

Post by pests »

locusofself wrote: post #115
_7tgr wrote: post #111

Earlier quoted context omitted.

This lists a few things using Java Cards (likely stuff that's in your wallet, surprisingly): https://stackoverflow.com/questions/47731005/practical-use-o... (fwiw I have a bit of prior experience here)

That's pretty neat. It sounds like Java Card (or at least some other cards) actually "boot up" by way of inductive coupling, ie, via the "contactless" card readers where you just hold your card in proximity to the reader thing. Did not know that, I assumed it was just reading a key via NFC or something.

This is a classic defcon talk about it. They developed their own cell network with their own sim cards for an event and even built custom JavaCard applications their users could use. They have released all their information and tools used to build and compile Java Card software.

https://www.youtube.com/watch?v=_-nxemBCcmU

Re: I have written a JVM in Rust

#125

Post by Sharlin »

locusofself wrote: post #115
_7tgr wrote: post #111

Earlier quoted context omitted.

This lists a few things using Java Cards (likely stuff that's in your wallet, surprisingly): https://stackoverflow.com/questions/47731005/practical-use-o... (fwiw I have a bit of prior experience here)

That's pretty neat. It sounds like Java Card (or at least some other cards) actually "boot up" by way of inductive coupling, ie, via the "contactless" card readers where you just hold your card in proximity to the reader thing. Did not know that, I assumed it was just reading a key via NFC or something.

The whole reason there’s a thing called a chip in the card is that it actually does computing (indeed they’re called smart cards) and that it does the sort of computing (cryptographic challenge-response) that makes these cards much more secure than oldschool magnetic stripe cards.

Even fully passive NFC tags contain logic that needs power to talk NFC back to the reader, there’s no such thing as just reading data via NFC.

Re: I have written a JVM in Rust

#126

Post by sn9 »

bingemaker wrote: post #81

When I see such cool projects, I feel very overwhelmed. How do you get started with Rust and master basics to even attempt doing such a thing? Can OP explain?

How much do you code in your free time? Like average hours per week?

If it's zero (and no judgement from me if it is; plenty of other things to focus on), then it shouldn't be surprising that someone for whom that number is (speculatively) 10-20 hours per week on average for years has impressive side projects.

Re: I have written a JVM in Rust

#127

Post by nerpderp82 »

pjmlp wrote: post #89
mike_hearn wrote: post #47

Earlier quoted context omitted.

Nope. For a more realistic example of such a JVM, look at SubstrateVM (written in "SystemJava" and compiled to native code ahead of time along with the app it runs), and "Java on Truffle" (a.k.a. Espresso), which is a JVM written in Java designed to be compiled to run on top of SubstrateVM. Both projects are a part of Graal. The reason to do this, beyond the inherently neat Inception factor, is that JVMs are a PITA t…

And Jikes RVM as well.

Jikes is extremely popular in academia for being the basis of VM research because it is so easy to modify.

https://github.com/JikesRVM/JikesRVM

Re: I have written a JVM in Rust

#128

Post by refulgentis »

locusofself wrote: post #107
unintendedcons wrote: post #100

Earlier quoted context omitted.

In what world did you convince yourself asking a chatbot was a source of real knowledge? respect yourself enough to look at primary sources

How about respect other people instead of rushing to condescending judgement? the stakes are incredibly low here, I asked ChatGPT for fun, like tens of millions of others are doing every day.

For some reason you announced that you were subjecting us to a low quality information retrieval method, and after 6 months of this, people are irritable. The social norms is to do that sort of thing in private, doing it in public and seemingly proudly came across as coarse and impolite

It didn't help any that it was clear from the initial post you were questioning someone with domain knowledge, which was later gently indicated to you

Re: I have written a JVM in Rust

#129

Post by arllk »

locusofself wrote: post #108
_7tgr wrote: post #98

Earlier quoted context omitted.

Google appears to be significantly more useful than GPT-4 here. [1] is the third result for me for the query "credit card jvm". [2] is the second result and gives a direct (and more importantly, actually correct) answer. That post links to the Oracle documentation for Java Cards [3] which is the fourth result. [1] https://en.m.wikipedia.org/wiki/Java_Card [2] https://superuser.com/questions/362567/are-there-any-credi…

Fair enough, there is a "Java Card". I'm not convinved that Java is running on any of my or your credit cards in your wallet today, though I'm not willing to bet on it.

It's running on many e-Passports and e-ID cards, i can't find the documentation from my e-ID card which runs on Java, but the chips are quite common like in

https://www.cardlogix.com/product/cardlogix-credentsys-lite-...

And on another source:

Visa became the first large payment company to license JavaCard. Visa mandated JavaCard for all of Visa’s smartcard payment cards. Later, MasterCard acquired Mondex, and Peter Hill joined as their CTO, licensed JavaCard, and ported the Mondex payment platform to JavaCard.

Source: https://javacardforum.com/2022/07/28/the-birth-of-javacard/

Re: I have written a JVM in Rust

#130

Post by xorcist »

locusofself wrote: post #108
_7tgr wrote: post #98

Earlier quoted context omitted.

Google appears to be significantly more useful than GPT-4 here. [1] is the third result for me for the query "credit card jvm". [2] is the second result and gives a direct (and more importantly, actually correct) answer. That post links to the Oracle documentation for Java Cards [3] which is the fourth result. [1] https://en.m.wikipedia.org/wiki/Java_Card [2] https://superuser.com/questions/362567/are-there-any-credi…

Fair enough, there is a "Java Card". I'm not convinved that Java is running on any of my or your credit cards in your wallet today, though I'm not willing to bet on it.

Just wait until you find out about the SIM card in your phone!

It's almost bizarre what that thing does.

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