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Reverse engineering the obfuscated TikTok VM

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412 points xfeeefeee | 2 comments | 21 Apr 25 01:59 UTC | HN request time: 0.492s | source
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Wowfunhappy ◴[21 Apr 25 10:38 UTC] No.43750333[source]▶
...can I ask a really stupid question? What is a VM in this context?

I've used VM's for years to run Windows on top of macOS or Linux on top of Windows or macOS on top of macOS when I need an isolated testing environment. I also know that Java works via the "Javascript Virtual Machine" which I've always thought of as "Java code actually runs in its own lightweight operating system on top of the host OS, which makes it OS-agnostic". The JVM can't run on bare metal because it doesn't have hardware drivers, but presumably it could if you wrote those drivers.

But presumably the VM being discussed in TFA isn't that kind of VM, right? Bytedance didn't write an operating system in Javascript?

I've been seeing "VM" used in lots of contexts like this recently and it makes me think I must be missing something, but it's the sort of question I don't know how to Google. AIs have not been helpful either, plus I don't trust them.

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1. yjftsjthsd-h ◴[21 Apr 25 15:43 UTC] No.43753234[source]▶
Nit:

> I also know that Java works via the "Javascript Virtual Machine"

Java Virtual machine. That Java and JavaScript are named the way they are is... basically a historical accident of a cross-promotion gone too far, IMO. They aren't really related (at least, in the way that the name might imply).

Now to your real question. Virtual machines are anything that is one computer pretending to be another computer. Sometimes, that's an x86_64 PC pretending to be another x86_64 PC to run a different OS. Sometimes that's an x86_64 PC pretending to be a 50-year-old mainframe ( https://opensimh.org/ really shines there). Sometimes it's an ARM laptop running macOS pretending to be an x86_64 PC so it can run Windows. And, relevant here, sometimes it's a phone pretending to be a machine that has never actually existed in hardware. You can just make up an imaginary machine that has any old characteristics you want. Maybe it has a built-in high-level network card that magically turns HTTP requests into responses without programs having to implement HTTP themselves. Maybe it has an imaginary graphics card that directly renders buttons. Maybe you imagine a CPU that runs Java opcodes directly. Whatever it is, if you can imagine a system and then write a program that emulates it, you can make a virtual machine and run stuff in it.

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2. Wowfunhappy ◴[21 Apr 25 18:19 UTC] No.43754852[source]▶
> Java Virtual machine. That Java and JavaScript are named the way they are is... basically a historical accident of a cross-promotion gone too far

Oops, that was a typo! Thank you.