Spin VS QEMU

git clone https://github.com/nimble-code/Spin.git cd Spin make

There are several choices for running code in partial or full isolation. Some languages include lightweight environments that do not interfere with each other, e.g., virtual environments in Python. However, due to caching and links, these are not sufficiently isolated for us. At the other end of the spectrum, we can run code in a node of a cloud computing service. However, the overhead and cost make this not worthwhile given our needs: isolation, but not very strong security requirements. Alternatively, we can run a virtual machine or emulator such as QEMU, VirtualBox, or others. This also has too much overhead given our needs.

Over the last year I have been rewriting QEMU's x86 decoder. I am now at a point where it should not be too hard to add APX support.

My decoder is mostly based on the tables in the manual, and the code is mostly okay—not too much indentation and phases mostly easy to separate/identify. Nevertheless there are several cases in which the manual is wrong or doesn't say the whole story.

The top comment explains a bit what's going on: https://github.com/qemu/qemu/blob/59084feb256c617063e0dbe7e6...

QEMU is an excellent open-source project that enables users to work on various projects across multiple platforms. Starting a VM instance with QEMU is straightforward. On my old Intel-based Mac, the following command will launch an Ubuntu cloud image:

Another important tool from the same organization is Vagrant, which provides extra help in running VMs built with Packer. Of course, the choice of a VM provider is also very important, as some VM providers may not be supported on certain platforms. For example, there are no VMware or VirtualBox releases that support Apple Silicon. However, QEMU is supported on most platforms, including Apple Silicon, which is why this provider was chosen here.

My most-wanted QEMU feature: https://github.com/qemu/qemu/commit/a2260983c6553

Using `gic-version=3` on macOS you can now use more than 8 cores on ARM chips.

A better solution is just to write a plain ass shell script that tests if various C snippets compile.

https://github.com/oilshell/oil/blob/master/configure

https://github.com/oilshell/oil/blob/master/build/detect-pwe...

Not an unholy mix of m4, shell, and C, all in the same file.

---

These are the same style as a the configure scripts that Fabrice Bellard wrote for tcc and QEMU.

They are plain ass shell scripts, because he actually understands the code he writes.

https://github.com/qemu/qemu/blob/master/configure

https://github.com/TinyCC/tinycc/blob/mob/configure

OCaml’s configure script is also “normal”.

You don’t have to copy and paste thousands of lines of GNU stuff that you don’t understand.

(copy of lobste.rs comment)

Related:

A fast Pascal (Delphi) WebAssembly interpreter:

https://github.com/marat1961/wasm

WASM-4:

https://github.com/aduros/wasm4

Curated list of awesome things regarding WebAssembly (wasm) ecosystem:

https://github.com/mbasso/awesome-wasm

Also, it would be nice if there was a WASM (soft) CPU for QEMU, which (if it existed!) would go here:

https://github.com/qemu/qemu/tree/master/target

> architectural registers are always updated

In tiny code, the guest registers (global TCG variables) are stored in the host's registers until you either call an helper which can access the CPU state or you return (`git grep la_global_sync`). This is the reason why QEMU is not so terribly slow.

But after a check, this also happens when you access the guest memory address space! https://github.com/qemu/qemu/blob/master/include/tcg/tcg-opc... (TCG_OPF_SIDE_EFFECTS is what matters)

But still, in the end, it's the same problem. What QEMU does, can be done in LLVM too. You could probably be more efficient in LLVM by using the exception handling mechanism (invoke and friends) to only serialize back to memory when there's an actual exception, at the cost of higher register pressure. More or less what we do here: https://rev.ng/downloads/bar-2019-paper.pdf