PowerPC: missing support for the 750CL's Paired Singles instruction.

[phire]

Paired Singles is an vector instruction set extension for PowerPC, developed as a lightweight alternative to AltiVec, only dealing with two single precision floats at a time. The extension was originally developed for Nintendo with the Gekko cpu found in the GameCube, and the Broadway and Espresso cpus in Nintendo's Wii and Wii-U support it too.

IBM also released the 750CL for non-Nintendo embedded customers with support for Paired Singles.

Documentation can be found here.

There is also an initial attempt at a paired singles support for llvm here.

[aquynh]

any plans for LLVM to include this fix yet?

let me know when this happens, so i will upgrade PPC core to have this supported. thanks.

[riptl]

Hi @aquynh, there is a second attempt to get paired-singles added to LLVM from last year it seems: https://reviews.llvm.org/D85137

Does Capstone depend on LLVM's disassembler? I would like to write a patch adding paired-singles support to Capstone.

Sorry for the necropost 🙂 This issue is still relevant to a small number of people working on Nintendo Wii reverse engineering.

[riptl]

Hi @kabeor, why was this closed?

[kabeor]

@terorie
Sorry, we are cleaning legacy issues. Cause there were 400+ issues, so I have to close some of the earliest issues and see who will reply and manual reopen. Welcome back, I will continue to work on your issue here :)

[kabeor]

@terorie I reviewed this issue, it's interesting. Can you do a PR to next branch for this?

[riptl]

@kabeor Sure, I'll revisit this. Last time I looked at it, I was stuck because I couldn't figure out how to re-run LLVM TableGen code generation to add the missing instructions without breaking other things.
The LLVM upstream attempt to modify the td files has diverged a lot from the Capstone codebase too.

[kabeor]

@terorie you can check this folder to see if it can help to do some thing.
Actually, these scripts in the folder still use some llvm 7.0 tools which is very old. I was wondering how to get it updated to lastest llvm 13 tools.

Please feel free to share if you have any thought about this.

[riptl]

Hey @kabeor, I've written TableGen definitions for all 750CL extension opcodes now. Unfortunately, LLVM 7.0.1 doesn't work anymore and is failing on unrelated code that I haven't touched. I think it might be due to an LLVM version mismatch. Can you confirm the correct LLVM version please?
Thanks 🙏🏻

./gen-tablegen-arch.sh ~/opt/llvm-project/llvm/build/bin/ PPC 
...
Generating PPCGenSubtargetInfo.inc
Included from PPC/PPC.td:298:
Included from PPC/PPCSchedule.td:138:
Included from PPC/PPCScheduleP9.td:13:
Included from PPC/PPCInstrInfo.td:3173:
PPC/PPCInstrHTM.td:25:18: error: Couldn't find class 'PPCCustomInserterPseudo'
def TBEGIN_RET : PPCCustomInserterPseudo<(outs gprc:$out), (ins u1imm:$R), "#TBEGIN_RET", []>;

[riptl]

I think this commit 839c5e2 creates a dependency on llvm/llvm-project@c7b43b9 which is only in LLVM 8.0

[riptl]

I see, I think hot fix #1510 uses a patched LLVM but it's not documented what the right version is.

[riptl]

My TableGen compiles now and I'm sending in a patch some time today. 🥳

[kabeor]

WoW, amazing. Looking forward to your PR:)