assembly VS llvm-project

When you're learning something for the first time, it can be hard to know what mental model you need to have to be effective with the tool.

Some documentation is reference material. With reference material you might navigate the reference material in a particular traversal to get what you need to do what you want.

But at the beginning of your journey, you need to be taught a "flow" an expected pattern of operation to build up the right mental model of how an average session with the tool works. For programming this might be the edit file, compile, run, debug loop, or TDD or IntelliJ's build and deploy. Or a CI system commit, push, deploy, promote cycle. Or kubernetes kubectl edit, apply.

I opened the "dining philosophers TLA+" example and ran it - this seemed to be an affordance of the TLA+ Toolbox GUI which was straightforward to understand.

But then I tried to use the tool with my own. I interpreted the existing code of the dining philosophers and tried to make my own ringbuffer model.

It took me a while that I needed to update this screen to put in the following details that I have filled in on the screenshot:

https://github.com/samsquire/assembly/blob/main/screenshots/...

You have to put your entrypoint in the "temporal formula" and then put your model arguments on the right hand side.

I was able to piece together the operation of this tool by piecing together various reference details together, it wasn't until I saw that screenshot I referenced in my OP that I realised I needed to do that step to get the PlusCal code to update the TLC code that follows it. I was wondering why it didn't work until I saw that screenshot.

Thank you for this in-depth article.

I am a less than a C++ beginner but I asked Stack Overflow how to run C++ coroutines in a thread pool. It seems coroutines in C++20 are unfinalised but don't quote me on that but I did get some sourcecode for older versions of the C++20 standard.

I used Marce's Col's excellent blog post about how to create coroutines in assembly by adjusting the RSP pointer.

https://blog.dziban.net/posts/coroutines/

I extended Marce's code to run the coroutines in kernel threads:

https://github.com/samsquire/assembly (see threadedcoroutines.S)

I have been thinking of coroutines in terms of query compilation for database engines and the volcano query model and this article:

https://www.chiark.greenend.org.uk/~sgtatham/coroutines.html

Tying together two pieces of code that call eachother in push or pull driven style is really powerful. Or if you're running multiple independent tasks that need their own state. This as I understand it is the original intent of object orientation that Alan Kay wanted and is represented by Erlang and partly Go.

Specifically, I am thinking of compiler created coroutines where code can be interleaved at compile time rather than at runtime.

Thank you for your ideas and thoughts.

This might be relevant - I've been playing around with some assembly to unwind the stack, but it occurred to me I don't need to pop the stack to scan through it. So like C++ exception handling (I learned about it in the Itanium C++ ABI) or algebraic effects, you can scan memory if you have access to the stack start in memory (I do that by storing the rsp somewhere in .global main) in theory it's just data.

I need to generate sections of lookup data for range information for associating .text code section addresses with function names.

In theory this would also be useful for coroutines since a coroutine position/state is just a program counter position of code that you can JMP to in your yield function (that isn't a call but an offset)

To move a coroutine from one thread to another or another machine over the network or persist to disk, let me think. We could do what C++ coroutines does and have a promise struct object that is presumably on the stack when a coroutine resumes by jumping to that coroutines location.

I think the hard part is being stackless and persisting the current coroutine state. You could mov $COMPILER_DETERMINED_OFFSET into -10(%rbp) that promise object and then when the coroutine resumes it does a JMP -10(%rbp) in a label before the coroutine body.

I am a beginner to assembly programming but here is my program: https://github.com/samsquire/assembly/blob/main/stackunwind....

https://github.com/samsquire/assembly/blob/main/coroutines.S

This might be useful to someone who wants to port this to C. This uses the stack switching idea. So they are stackful coroutines.

There's also Tina a header only coroutine library

As far as I know, libstdc++'s representation has two advantages:

First, it simplifies the implementation of `s.data()`, because you hold a pointer that invariably points to the first character of the data. The pointer-less version needs to do a branch there. Compare libstdc++ [1] to libc++ [2].

[1]: https://github.com/gcc-mirror/gcc/blob/065dddc/libstdc++-v3/...

[2]: https://github.com/llvm/llvm-project/blob/1a96179/libcxx/inc...

Basically libstdc++ is paying an extra 8 bytes of storage, and losing trivial relocatability, in exchange for one fewer branch every time you access the string's characters. I imagine that the performance impact of that extra branch is tiny, and massively confounded in practice by unrelated factors that are clearly on libc++'s side (e.g. libc++'s SSO buffer is 7 bytes bigger, despite libc++'s string object itself being smaller). But it's there.

The second advantage is that libstdc++ already did it that way, and to change it would be an ABI break; so now they're stuck with it. I mean, obviously that's not an "advantage" in the intuitive sense; but it's functionally equivalent to an advantage, in that it's a very strong technical answer to the question "Why doesn't libstdc++ just switch to doing it libc++'s way?"

This Ruby implementation is based on mruby and LLVM and it’s commercial software but cheap.

'Computer Architeture: A Quantitative Apporach" and/or more specific design types (mips, arm, etc) can be found under the Morgan Kaufmann Series in Computer Architeture and Design.

"Getting Started with LLVM Core Libraries: Get to Grips With Llvm Essentials and Use the Core Libraries to Build Advanced Tools "

"The Architecture of Open Source Applications (Volume 1) : LLVM" https://aosabook.org/en/v1/llvm.html

"Tourist Guide to LLVM source code" : https://blog.regehr.org/archives/1453

llvm home page : https://llvm.org/

llvm tutorial : https://llvm.org/docs/tutorial/

llvm reference : https://llvm.org/docs/LangRef.html

learn by examples : C source code to 'llvm' bitcode : https://stackoverflow.com/questions/9148890/how-to-make-clan...

See

https://github.com/llvm/llvm-project/issues/88344

https://fortran-lang.discourse.group/t/flang-new-how-to-forc...

You can never mistake type_declaration with an identifier, otherwise the program will not work. Aside from that constraint, you are free to name them whatever you like, there is no one standard, and each parser has it own naming conventions, unless you are planning to use something like LLVM. If you are interested, you can see examples of naming in different language parsers in the AST Explorer.

> There is one way to make the LLVM JIT compiler more usable, but I fear it’s going to take years to be implemented: being able to cache and reuse compiled queries.

Actually, it's implemented in LLVM for years :) https://github.com/llvm/llvm-project/commit/a98546ebcd2a692e...

> It's true, this was a CVE in Rust and not a CVE in C++, but only because C++ doesn't regard the issue as a problem at all. The problem definitely exists in C++, but it's not acknowledged as a problem, let alone fixed.

Can you find a link that substantiates your claim? You're throwing out some heavy accusations here that don't seem to match reality at all.

Case in point, this was fixed in both major C++ libraries:

https://github.com/gcc-mirror/gcc/commit/ebf6175464768983a2d...

https://github.com/llvm/llvm-project/commit/4f67a909902d8ab9...

So what C++ community refused to regard this as an issue and refused to fix it? Where is your supporting evidence for your claims?

For everyone else looking for the magic in this almost 7k lines monster, look at line 6610 [1].

[1] https://github.com/llvm/llvm-project/blob/8ec28af8eaff5acd0d...