Add RV64M instructions

[cyuria]

See title

[ThestralWarrior]

Hi, I want to contribute to this project. I have knowledge of x64 so RISC-V shouldn't be too difficult to pick up. How should I proceed with this? It's my first time trying open source and I could use some guidance!

[cyuria]

No worries, I really still need to fix up a lot of docs for contributing and stuff. Not to mention general usage docs 👀

The latest official RISC-V specs can be found here https://riscv.org/technical/specifications/, there's a chapter (ch13, page 65/84) on the RV64M extension on volume 1 (the unprivileged specification).

Have a look through https://github.com/cyuria/wrasm/blob/cddaa9f9248c5943e84f5359f95df250da5e016d/src/form/rv64i.c and the corresponding header file. Pretty much this issue is to create a new file (maybe called src/form/rv64m.c) and create the equivalent RISC-V bytecode generation functions and data structure.

Also make sure to add the instruction set to src/form/instructions.c (under the sets array). That'll make sure the assembly parser can actually find the instructions.

If you want to use any of the functions in src/form/rv64i.c, go ahead, but consider if they should be moved to src/form/generic.c instead.

One more thing is I'm currently working on overhauling the argument parsing, I'm happy to deal with any merge conflicts, but if you are on top of everything else I've just mentioned it would be fantastic if you could quickly check out this branch https://github.com/cyuria/wrasm/tree/11-implement-per-instruction-argument-parsing and make my life a bit easier 😃.

If you have any questions at all just let me know (including about the risc-v spec, it took me a while to wrap my head around a lot of the stuff in it).

[cyuria]

Oh also please write some unit tests under test/unit, for reference, here are my current unit tests for the rv64i instruction set https://github.com/cyuria/wrasm/blob/cddaa9f9248c5943e84f5359f95df250da5e016d/test/unit/form_rv64i.c

You might notice I'm not very good at writing tests but I have a few so that's there at least. To get the bytecode I created a tiny assembly file with the instructions I wanted and then used clang + llvm-objdump to assemble and then get the bytes and disassembly. The tests don't need to (and probably shouldn't) be exhaustive just make sure the right bytes are in the right place for the right instruction, it's mainly just to prevent regressions and make sure the code you write actually works.

If you also want you can add/change some tests under test/system. Basically there's a bunch of assembly (well a hello world file at least) and I just assemble and run it. You don't need to do this though, it requires qemu emulation binaries and lld (the llvm linker) to run (see the python script in said directory).

Sorry for writing so much, this should really be in CONTRIBUTING.md or something

[cyuria]

Oh also https://github.com/riscv-non-isa/riscv-asm-manual/blob/main/riscv-asm.md#user-content-fn-1-a43cd0e951dba5ca7a7ce7a0471ba5fc has some pseudo instructions and stuff, it might be worth having a look through it at some point.

Thanks for offering to help, I appreciate it.

[cyuria]

I just opened up a draft PR #12 for the new assembly instruction argument parsing functionality I'm writing so you can click on that instead of trying to find the right branch

[ThestralWarrior]

Okay thank you! I will go through these.

[cyuria]

Update just to let you know I've merged #12 into master, also I had a quick look at the chapter on the multiplication and division instruction set and it seems like you won't need to actually implement anything, just maybe move the form_itype function to src/form/generic.c and put together the instruction definitions and add some preprocessor definitions etc. etc, just housekeeping stuff really and making sure everything works

[cyuria]

Sorry to give you so much stuff to read through, you only really need to have a look through the source code and the specific parts of the spec, but also chapter 34 of the RISC-V spec outlines the actual bits which need to be set so you'll probably want to have a look through there as well at some point (it's probably the most useful chapter in the whole spec for this particular project).

I should've maybe clarified I don't expect you to know the spec (I barely understand the basics myself and I've been working on this assembler for 4 months), you really only need to go over the two chapters (13 and 34), which should have all the info you need to get started with writing some code.