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> If you're building code specifically to run in emulation, use RISC-V: builds faster, smaller code, runs faster.

I don't really think this bears out in practice. RISC-V is easy to emulate but this does not make it fast to emulate. Emulation performance is largely dominated by other factors where RISC-V does not uniquely dominate.

Interesting to see the gcc version gap between the targets. The x86_64 image shipping gcc 15.2.0 vs 7.3.0 on riscv64 makes the performance comparison less apples-to-apples than it looks - newer gcc versions have significantly better optimization passes, especially for register allocation.

MIPS (the arch of which RISCV is mostly a copy) is even easier to emulate, unlike RV it does not scatter immediate bits al over the instruction word, making it easier for an emulator to get immediates. If you need emulated perf, MIPS is the easiest of all

> The thing I most want to use this (or some other WASM Linux engine) for is running a coding agent against a virtual operating system directly in my browser.

That exists: https://github.com/container2wasm/container2wasm

Unfortunately I found the performance to be enough of an issue that I did not look much further into it.

Simon, this HN post didn't need to be about Gen AI.

This thing is really inescapable those days.

Check out Jeff Lindsay's Apptron (https://github.com/tractordev/apptron), comes very close to this, and is some great tech all on its own.

We are working on exactly this: https://browserpod.io

For a full-stack demo see: https://vitedemo.browserpod.io/

To get an idea of our previous work: https://webvm.io

I run agents as a separate Linux user. So they can blow up their own home directory, but not mine. I think that's what most people are actually trying to solve with sandboxing.

(I assume this works on Macs too, both being Unixes, roughly speaking :)

> The thing I most want to use this (or some other WASM Linux engine) for is running a coding agent against a virtual operating system directly in my browser.

Well, there it is, the dumbest thing I'll read on the internet all week.

Most of the engineering in Linux revolves around efficiently managing hardware interfaces to build up higher-level primitives, upon which your browser builds even higher-level primitives, that you want to use to simulate an x86 and attached devices, so you can start the process again? Somewhere (everywhere), hardware engineers are weeping. I'll bet you can't name a single advantage such a system would have over cloud hosting or a local Docker instance.

Even worse, you want this so your cloud-hosted imaginary friend can boil a medium-sized pond while taking the joyful bits of software development away from you, all for the enrichment of some of the most ethically-challenged members of the human race, and the fawning investors who keep tossing other people's capital at them? Our species has perhaps jumped the shark.

Are you describing bolt.new? (Unfortunately, it looks like their open source project is lagging behind https://github.com/stackblitz-labs/bolt.diy)

While this may be a better sandbox, actually having a separate computer dedicated to the task seems like a better solution still and you will get better performance.

Besides, prompt injection or simpler exploits should be addressed first than making a virtual computer in a browser and if you are simulating a whole computer you have a huge performance hit as another trade off.

On the other hand using the browser sandbox that also offers a UI / UX that the foundation models have in their apps would ease their own development time and be an easy win for them.

It's relatively easy to spin up a busybox WASM v86 solution

This is not the technical solution you want, but I think it provides the result that you want: https://github.com/devcontainers

tldr; devcontainers let you completely containerize your development environment. You can run them on Linux natively, or you can run them on rented computers (there are some providers, such as GitHub Codespaces) or you can also run them in a VM (which is what you will be stuck with on a Mac anyways - but reportedly performance is still great).

All CLI dev tools (including things like Neovim) work out of the box, but also many/most GUI IDEs support working with devcontainers (in this case, the GUI is usually not containerized, or at least does not live in the same container. Although on Linux you can do that also with Flatpak. And for instance GitHub Codespaces runs a VsCode fully in the browser for you which is another way to sandbox it on both ends).

My god that interface feels like home.

Yeah. Microsoft really went downhill UI-wise.

win2000 brings back so many good memories.

Is that even remotely relevant to JSLinux?

https://github.com/copy/v86 might be a more 1:1 fully open sourced alternative.

"he didn't attach the source code for the 64-bit x86 emulation layer"

It's not open source? If that's the case, it should be in his FAQ.

Wow, thanks for this, this is exactly what v86 was missing! Runs faster than my demo: https://zb3.me/qemu-wasm-test/jspi-noffi/

Even though it has no JIT. Truly magic :)

From the "Technical notes" page:

> Access to Internet is possible inside the emulator. It uses the websocket VPN offered by Benjamin Burns (see his blog). The bandwidth is capped to 40 kB/s and at most two connections are allowed per public IP address. Please don't abuse the service.

https://bellard.org/jslinux/tech.html

A somewhat better solution via tailnet you can find in https://webvm.io/

I use bellard.org/jslinux to test compilation of strange code sometimes[1], since it came with compilers that are different versions from what I have installed locally, and it's easier to open up a browser than starting a VM.

[1] For example:

https://www.ioccc.org/2020/yang/index.html#:~:text=tcc%200.9...

https://www.ioccc.org/2018/yang/index.html#:~:text=tcc%200.9...

I use a similar emulator (v86) as a way to share my hobby OS. Approximately zero people, even my friends, are going to boot my hobby OS on real hardware; I did manage to convince some of them to run it in qemu, but it's difficult. A browser environment shows the thing quite well; and easy networking is cool too.

My hobby OS itself is not very useful, but it's fun if you're in the right mood.

I guess for the author its learning about how Linux can be ported to the browser. For us, it's more of a nice amusement.

But then again, I've never understood why Buddhist monks create sand mandalas[1] and then let them be blown away (the mandalas not the monks!).

I think one should see it from the authors PoV instead of thinking "what is in it for me". If I were to use this, then to create digital sand mandalas in the browser! ;)

[1]: https://en.wikipedia.org/wiki/Sand_mandala

We are a playful species. People enjoy play. If we didn't have to work for a living but still enjoyed food security that is all most of us would do. But we are also a very exploitative species, some more than others. Companies have made billions of dollars on top of Fabrice Bellard's works, qemu, ffmpeg etc.

These companies don't have any imagination. Their management has no vision. They could not create anything new and wonderful if they tried. People like Fabrice do and we are all richer for it. If your asking about the practical use you are likely in the exploitative mindset which is understandable on HN. The hacker/geek mindset enjoys this for what it is.

https://infinitemac.org/ is an example of a good use: users can try out old versions of Mac OS, to see what's changed and what software used to be available for old versions. It doesn't use JSLinux, but other emulators [1]

[1] https://blog.persistent.info/2025/03/infinite-mac-os-x.html

Most such emulators have Internet access on the IP level. Therefore, this is a very cheap way to test anything on the Internet.

    apk add nmap
    nmap your.domain.com

It can also be used as a very cheap way to provide a complete build environment on a single website, for example to teach C/C++. Or to learn the shell. You don't have to install anything.

Agentic workloads create and then run code. You don't want to just run that code in a "normal" environment like a container, or even a very well protected VM. There are other options, ofc - eg. gvisor, crossvm, firecracker, etc, but this one is uncommon enough to have a small number of attackers trying to hack it.

Some sort of web based archive of applications/etc where you can boot them up in your browser.

Maybe if you’ve got some ancient software that’s missing source code and only runs with X Y and Z conditions, you could continue to offer it on the web and build around it like that? Not sure if that would be practical at all, but could be interesting

My college professor used it to teach us the Linux command line

We have Windows PCs in the classroom.