Port CoreCLR PAL to linux-riscv64

[am11]

The first component in coreclr port is the abstraction layer located at src/coreclr/pal. That enables us to port other components of coreclr such as src/coreclr/vm, src/coreclr/unwinder and ultimately src/coreclr/jit.

We have riscv64 cross-toolchain with prerequisites set up for building the runtime. Some initial strokes to port coreclr are checked into the main branch (cmake configurations, libunwind, a few definitions in pal.h etc.).

Here is a gist for cross compilation:

#!/bin/sh

# on Ubuntu amd64 - with curl, jq and docker installed

tag="$(curl -sSL "https://raw.githubusercontent.com/dotnet/versions/main/build-info/docker/image-info.dotnet-dotnet-buildtools-prereqs-docker-main.json" |\
  jq -r '.repos[] | .images[] | .platforms [] | select(.dockerfile | contains("riscv64")).simpleTags[0]')"

URN="mcr.microsoft.com/dotnet-buildtools/prereqs:$tag"

cd runtime  # current main branch of dotnet/runtime

# Only build coreclr PAL and its tests:
docker run --rm -e ROOTFS_DIR=/crossrootfs/riscv64 -v"$(pwd)":/runtime "$URN" \
  /runtime/src/coreclr/build-runtime.sh -cross -a riscv64 -component paltests

# note: /crossrootfs/riscv64 has Debian sid bootstrap environment with llvm 14 and few other dependencies
# and the host has llvm 15 toolchain, which will be used by cmake for compilation with
# -sysroot=/crossrootfs/riscv64
#
# the relevant code to build this prerequisites docker image are:
#   * https://github.com/dotnet/arcade/blob/2e7521a/eng/common/cross/build-rootfs.sh#L155
#   * https://github.com/dotnet/arcade/blob/2e7521a/eng/common/cross/toolchain.cmake#L64
#   * https://github.com/dotnet/dotnet-buildtools-prereqs-docker/tree/main/src/ubuntu/22.04/cross/riscv64

The missing parts are architecture-specific assembly code under src/coreclr/pal/src/arch/riscv64, src/coreclr/pal/inc/unixasmmacrosriscv64.inc among other things. We added placeholder assembly files with #error TODO-RISCV64​ which can be reviewed and deleted as part of the port.

Once PAL port is completed, we can copy artifacts/bin​ to riscv64 machine (or virtual machine) and run its tests to verify the state of port:

$ artifacts/bin/coreclr/Linux.riscv64.Debug/paltests/runpaltests.sh \
    $(pwd)/artifacts/bin/coreclr/Linux.riscv64.Debug/paltests

[alexrp]

Once PAL port is completed, we can copy artifacts/bin​ to riscv64 machine (or virtual machine)

For porting of this nature, qemu-riscv64 is your best friend. You can write code on an x86-based Linux system, build with a RISC-V cross toolchain, and then just run the resulting binary with QEMU's user mode emulation. I wrote a bit about this here for Mono a few years back.

[am11]

Yup, I am using debian sid riscv64 virtual machine. They also have good documentation in their wiki: https://wiki.debian.org/RISC-V#Qemu

RISC-V laptops are rumored to be available in coming weeks. :)

[archanox]

Fantastic work @am11! Looking forward to seeing how far dotnet support on RISC-V goes!

[am11]

I will defer to someone with experience to take the lead. I am new to RISC-V assembly but can lend hand wherever possible. :)

[jkotas]

Anything left to do here?

[ghost]

Due to lack of recent activity, this issue has been marked as a candidate for backlog cleanup. It will be closed if no further activity occurs within 14 more days. Any new comment (by anyone, not necessarily the author) will undo this process.

This process is part of our issue cleanup automation.

[gbalykov]

Anything left to do here?

@jkotas I think all is done. I'll share current pal tests status here soon.

[am11]

@gbalykov we can continue at #84834 and close this one?

[gbalykov]

Current pal tests results on main

1) x64

PAL Test Results:
  Passed: 435
  Failed: 0

2) riscv visionfive2 with HAVE_FUNCTIONAL_PTHREAD_ROBUST_MUTEXES_EXITCODE 1

PAL Test Results:
  Passed: 436
  Failed: 0

3) riscv visionfive2 with HAVE_FUNCTIONAL_PTHREAD_ROBUST_MUTEXES_EXITCODE 0

PAL Test Results:
  Passed: 436
  Failed: 0

So, all is done.

[am11]

Amazing progress! Lets continue monitoring the status of overall runtime tests at #84834. Closing.