Figure out what's needed to support `rustc`

[elfprince13]

Rust seems like an attractive language to support on TI Calculators (and other (e)Z80 platforms):

• It's a "systems" language like C and C++
• It benefits from many years of research in programming language design to enable writing code that is safer and more robust than similar C/C++ code.
• There appears to be an active community for embedded rust.
• rustc emits LLVM IR, so it seems like we should be able to try and hook things up!

Therefore, I'm opening this issue to try and get the discussion moving forward!

[tari]

It's documented in the rustc dev guide: https://rustc-dev-guide.rust-lang.org/building/new-target.html

[elfprince13]

Thanks @tari!

@jacobly0 - do you have a thread somewhere tracking progress your backends, and what should be expected to work/not work? I'm assuming that if TI Planet's Project Builder now supports C++17 / clang, things are in a decent shape?

[adriweb]

TI-Planet's PB is just using the llvm branch of the toolchain, but yes there hasn't been much trouble lately, so it's in pretty good shape I'd say. We're not necessarily far from a releasable state, compiler+toolchain wise.

[mrk-its]

You may try to compile rust code as described here: http://forum.6502.org/viewtopic.php?p=84048#p84048

6502 backend is very incomplete yet, but I was able to produce working executable this way. The trick is to compile rust code to llvm-ir first (.ll file) and then link it using your llvm fork.

[Serentty]

I was able to build a crate using Cargo and then use this method to have Clang compile and link all of the IR files. Unfortunately this means I still don't have access to the core library. There's also the issue that all I can figure out how to get is assembly in GAS syntax which I don't know of any Z80 assembler for. Still, it's fascinating to read through the generated code.

[elfprince13]

@Serentty - which method did you try? The one linked by @tari sounds like it should be able to produce a cross-compiler that can handle core too?

[Serentty]

I tried that. I followed along with the changes made by @mrk-its to make a Rust compiler for the 6502 in his form, but for the Z80 instead. But unfortunately, I just ended up getting LLVM to segfault when I tried that. So I just wrote a custom JSON target specification (telling it that it was ARM, but changing all the data sizes to match the Z80), got it to generate IR, and then fed that into Clang.

[dtomvan]

I tried compiling core from the rust stdlib for the ti-84: here

However, llc outputs this:

tools/llc: /usr/lib/libtinfo.so.6: no version information available (required by tools/llc)
LLVM ERROR: unable to translate instruction: ret (in function: _ZN4core6result19Result$LT$T$C$E$GT$6unwrap17h902768c9e7854d83E)
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace.
Stack dump:
0.      Program arguments: tools/llc incremental/ti_84_poc-a6bfe995eb836153.ll -o ./incremental/ti_84_poc.s
1.      Running pass 'Function Pass Manager' on module 'incremental/ti_84_poc-a6bfe995eb836153.ll'.
2.      Running pass 'IRTranslator' on function '@"_ZN4core6result19Result$LT$T$C$E$GT$6unwrap17h902768c9e7854d83E"'
 #0 0x000000000166c653 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (tools/llc+0x166c653)
 #1 0x000000000166a57e llvm::sys::RunSignalHandlers() (tools/llc+0x166a57e)
 #2 0x000000000166caff SignalHandler(int) (tools/llc+0x166caff)
 #3 0x00007feb2d964870 __restore_rt (/usr/lib/libpthread.so.0+0x13870)
 #4 0x00007feb2d5c4d22 raise (/usr/lib/libc.so.6+0x3cd22)
 #5 0x00007feb2d5ae862 abort (/usr/lib/libc.so.6+0x26862)
 #6 0x00000000015e9919 (tools/llc+0x15e9919)
 #7 0x00000000015e9937 (tools/llc+0x15e9937)
 #8 0x00000000018c4a4a (tools/llc+0x18c4a4a)
 #9 0x00000000018d5e88 llvm::IRTranslator::runOnMachineFunction(llvm::MachineFunction&) (tools/llc+0x18d5e88)
#10 0x0000000000bbc26e llvm::MachineFunctionPass::runOnFunction(llvm::Function&) (tools/llc+0xbbc26e)
#11 0x0000000000f68f5d llvm::FPPassManager::runOnFunction(llvm::Function&) (tools/llc+0xf68f5d)
#12 0x0000000000f6ecf3 llvm::FPPassManager::runOnModule(llvm::Module&) (tools/llc+0xf6ecf3)
#13 0x0000000000f6959f llvm::legacy::PassManagerImpl::run(llvm::Module&) (tools/llc+0xf6959f)
#14 0x000000000081e683 main (tools/llc+0x81e683)
#15 0x00007feb2d5afb25 __libc_start_main (/usr/lib/libc.so.6+0x27b25)
#16 0x0000000000819eae _start (tools/llc+0x819eae)
/tmp/tomvd/fsio/CHns2yiOPZ.sh: line 5: 67714 Aborted                 (core dumped) tools/llc $(find incremental -name ${CARGO_MAKE_PROJECT_NAME}-*.ll) -o ./incremental/${CARGO_MAKE_PROJECT_NAME}.s

[dtomvan]

The person I forked this from to try out called it "a proof of concept" but then I start using the core library (I updated the compiler to the latest commit, see my fork) and it does not work properly. LLVM seems to not understand this ret instruction.

[adriweb]

The asm generated by the compiler, when targeting (e)z80, is made for the fasmg assembler with specific support for that target, see for example how it's used in here: https://github.com/CE-Programming/toolchain

[dtomvan]

Which compiler are you talking about exactly? rustc or llc

Edit: maybe related to this? rust-lang/rust#58567

[jacobly0]

That error means that the calling convention code didn't support however the function was trying to return.

[sbechet]

Hello,

maybe it can help as an example: rust-lang/rust#88321