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The LLVM m88k backend implementation

This repository contains the current state of my m88k backend for LLVM. For general information about LLVM, please read README.md.

The Motorola 88000 is a RISC architecture developed by Motorola in the late 1980s. See Wikipedia for a general overview.

The code is based on the example from my book "Learn LLVM 12" (see O'Reilly, Packt or Amazon). It differs in the following ways:

  • Uses only GlobalISel. SelectionDAG support has been removed.
  • Minimal clang support. Makes it easy to crash the backend.
  • All machine instructions are implemented.
  • Assembler supports .requires81100 directive.
  • Updates/refactoring of AsmParser, register definition, calling convention, etc.
  • Removed all Itineries in favor of the new scheduling model.

Building LLVM with the m88k backend

The m88k backend is added as experimental backend to LLVM, named M88k. It's prefined in the CMake files, but if you want to compile other experimental targets, too, then you have to pass option

-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD="M88k"

to CMake.

Development

The main development happens in branch main-m88k. The branch release/13.x-m88k contains an older state based on LLVM 13.x. The branch release/12.x-m88k contains the source from my book on top of LLVM 12.x.

This repository mirrors the LLVM main and release/* branches. I keep my files on top of main, which means that I often rebase. Sorry!

Status

The benchmark MiBench/security-sha from the LLVM test suite can be cross-compiled with optimization levels -O0, -O1, and -O2, and gives the same result as the native gcc-compiled version. Here is the recipe:

  1. Create a directory for the header files. From here I name it $SYSROOT.
  2. Copy directory /usr/include (with all subdirectories) from your OpenBSD system to your development system into the directory $SYSROOT/usr/include.
  3. Change into the LLVM test suite into directory MultiSource/Benchmarks/MiBench/security-sha, and compile the test case: clang -target m88k-openbsd --sysroot=$SYSROOT -c sha*.c
  4. Copy the object files back to your OpenBSD system.
  5. Link the object files: gcc -o sha sha*.o
  6. Run the test case, e.g. ./sha /etc/rc
  7. To verify the result you can copy the test case source to your OpenBSD system, compile the files with gcc, run the programm on the same file and compare the result.

Other test cases and optimization levels may work but there is still a lot to implement before significant more test cases function correctly.

Support

If you like this work, then there are several ways you can support me:

  • You can contributes patches.
  • You can provide access to real hardware, e.g. as ssh login.
  • If you find some documentation (e.g. the ABI updates from 88open) I would be happy to receive a copy.
  • You can buy me a beer or a coffee.

General information about m88k

Programming manuals

You can find the user manuals for the 88100 and 88110 CPUs, the 88200 MMU and the 88410 secondary cache controller at bitsavers: https://www.bitsavers.org/components/motorola/88000/. The manual for the 88110 CPU and the 88410 cache controller are also available on GitHub: https://github.com/awesome-cpus/awesome-cpus-m88k. Some of the files can also be found on https://archive.org/.

The ELF ABI is only available at https://archive.org/details/bitsavers_attunixSysa0138776555SystemVRelease488000ABI1990_8011463.

The book Programming the Motorola 88000 by Michael Tucker and Bruce Coorpender (ISBN-13: 978-0830635337, ISBN-10: 0830635335) is out of print.

In the book Microprocessor Architectures, 2nd Edition by Steve Heath, you find a description of the M88000 architecture in chapter 3.

Regarding the ABI, there were some changes made by the 88open consortium. I have not yet found that documents. If you have some of them then please contact me!

Systems

The OpenBSD/luna88k port is still active and provides the latest OS releases. On a Linux or FreeBSD machine, you can use GXemul to run OpenBSD/luna88k. Alternatively you can use the LUNA emulator nono. Kenji Aoyama provides a live image which can be used with both emulators.

You can find information about real hardware at m88k.com.

Toolchain

gcc 3.3.6 is last version with support for the m88k architecture. See the manual page at https://gcc.gnu.org/onlinedocs/gcc-3.3.6/gcc/M88K-Options.html#M88K-Options.

You can download that version from ftp:https://ftp.nluug.nl/mirror/languages/gcc/releases/gcc-3.3.6/gcc-3.3.6.tar.gz

binutils 2.16 is last version with support for the m88k architecture. See the manual page at https://sourceware.org/binutils/docs-2.16/

You can download that version from https://ftp.gnu.org/gnu/binutils/binutils-2.16.1a.tar.bz2, and browse the source at https://sourceware.org/git/?p=binutils-gdb.git;a=tree;h=a7e286b9ab6d33e8261bfadc992d5bf753b36e9f;hb=a783ed1a1ba08d73583da5a56470e4af5acfb6bd.

Implementation

The backend is implementated like all other LLVM backends. The main classes involved are:

   classDiagram
      TargetPassConfig <|-- M88kPassConfig
      M88kPassConfig .. M88kTargetMachine
      LLVMTargetMachine <|-- M88kTargetMachine
      TargetLowering <|-- M88kTargetLowering
      TargetLoweringObjectFileELF .. M88kTargetMachine
      M88kGenSubtargetInfo <|-- M88kSubtarget
      M88kGenInstrInfo <|-- M88kInstrInfo
      M88kGenRegisterInfo <|-- M88kRegisterInfo
      M88kTargetMachine --> M88kSubtarget
      M88kSubtarget o-- M88kInstrInfo
      M88kSubtarget o-- M88kTargetLowering
      M88kInstrInfo o-- M88kRegisterInfo
      class M88kTargetMachine{
         +getSubtargetImpl() M88kSubtarget
         +createPassConfig() TargetPassConfig
         +getObjFileLowering() TargetLoweringObjectFile
      }
      class M88kSubtarget{
         -M88kFrameLowering FrameLowering
         -M88kInstrInfo InstrInfo
         +getTargetLowering() M88kTargetLowering
         +getInstrInfo() M88kInstrInfo
      }
      class M88kInstrInfo{
         -M88kRegisterInfo RI
         +getRegisterInfo() M88kRegisterInfo
      }
      class M88kGenSubtargetInfo{
         <<Generated>>
      }
      class M88kGenInstrInfo{
         <<Generated>>
      }
      class M88kGenRegisterInfo{
         <<Generated>>
      }
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The M88kSubtarget also owns the main passes for GlobalISel:

   classDiagram
      M88kSubtarget o-- M88kCallLowering
      M88kSubtarget o-- M88kM88kLegalizerInfo
      M88kSubtarget o-- M88kRegisterBankInfo
      M88kSubtarget o-- M88kInstructionSelector
      M88kGenSubtargetInfo <|-- M88kSubtarget
      class M88kSubtarget{
         -std::unique_ptr~CallLowering~ CallLoweringInfo
         -std::unique_ptr~LegalizerInfo~ Legalizer
         -std::unique_ptr~RegisterBankInfo~ RegBankInfo
         -std::unique_ptr~InstructionSelector~ InstSelector
         +getCallLowering() CallLowering
         +getRegBankInfo() RegisterBankInfo
         +getLegalizerInfo() LegalizerInfo
         +getInstructionSelector() InstructionSelector
      }
      class M88kCallLowering{
      }
      class M88kM88kLegalizerInfo{
      }
      class M88kRegisterBankInfo{
      }
      class M88kInstructionSelector{
      }
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