Add RISC-V (64-bit) support

[benz0li]

Create linux/riscv64 docker images.

[benz0li]

Currently, there is no official support for GHC on Linux/RISC-V:

• https://gitlab.haskell.org/ghc/ghc/-/issues/16783
  • https://gitlab.haskell.org/ghc/ghc/-/issues/23519

[benz0li]

This requires cross-compiling GHC¹ from either linux/amd64 or linux/arm64/v8 to linux/riscv64.

This is quite a lot of work and to compile it in a reasonable time, 'native RISC-V hardware'² is required.
👉 IMHO Docker/QEMU emulation is just not suitable for such a compilation effort.

@bgamari @mpickering Is cross-compiling GHC to Linux/RISC-V currently even possible?

ℹ️ 2024-08-22: Debian sid has GHC 9.4.7 for riscv64 in its package repository.

Footnotes

1. On Alpine Linux using the GHC musl images. ↩

2. On its way ↩

[mpickering]

I believe you can cross-compiler to RISC-V using the LLVM backend (your linked ticket seems to suggest that people do this).

[benz0li]

@supersven At some point I would like to add a linux/riscv64 image to the Alpine-based GHC musl docker manifest.

There is not much documentation about 'porting GHC'¹ to a new architecture using hadrian. Any hints/tips?

Dockerfile to build GHC 9.10.1 for both linux/amd64 and linux/arm64/v8: https://github.com/benz0li/ghc-musl/blob/6f4d9658c96f16a6a9ed5d577512a147adf4ccaf/latest.Dockerfile

Footnotes

1. Cross-compiling GHC itself ↩

[supersven]

I believe you can cross-compiler to RISC-V using the LLVM backend (your linked ticket seems to suggest that people do this).

To shed some light on this:
GHC can cross-compile to RISC-V, with both the LLVM and NCG backends. However, GHC itself cannot be cross-compiled. The autoconf scripts do not allow that:

configure: error:
You've selected:

  BUILD:  x86_64-unknown-linux   (the architecture we're building on)
  HOST:   riscv64-unknown-linux    (the architecture the compiler we're building will execute on)
  TARGET: riscv64-unknown-linux  (the architecture the compiler we're building will produce code for)

BUILD must equal HOST; that is, we do not support building GHC itself
with a cross-compiler.  To cross-compile GHC itself, set TARGET: stage
1 will be a cross-compiler, and stage 2 will be the cross-compiled
GHC.

So, the only way to get a GHC bindist (for a recent GHC version) is to create it on real hardware (or an emulated VM, e.g. Qemu.)

If you got RISCV-V hardware, this shouldn't be much of an issue: Distributions like SuSE or Debian ship GHC with the LLVM backend configured. Though, be prepared that building and bundling with take about a day (without running the testsuite.)

As you likely want to ship only from trusted sources, I fear you'll need to wait until either Hadrian allows build != host builds. Or, we got a RISC-V CI runner.

So, I'd be excited to see a GHC/RISC-V Docker image (thanks a lot for bringing this up, BTW 👍 ), but we probably aren't ready, yet.

[benz0li]

I believe you can cross-compiler to RISC-V using the LLVM backend (your linked ticket seems to suggest that people do this).

To shed some light on this: GHC can cross-compile to RISC-V, with both the LLVM and NCG backends. However, GHC itself cannot be cross-compiled. The autoconf scripts do not allow that:

configure: error:
You've selected:

  BUILD:  x86_64-unknown-linux   (the architecture we're building on)
  HOST:   riscv64-unknown-linux    (the architecture the compiler we're building will execute on)
  TARGET: riscv64-unknown-linux  (the architecture the compiler we're building will produce code for)

BUILD must equal HOST; that is, we do not support building GHC itself
with a cross-compiler.  To cross-compile GHC itself, set TARGET: stage
1 will be a cross-compiler, and stage 2 will be the cross-compiled
GHC.

According to https://gitlab.haskell.org/ghc/ghc/-/wikis/cross-compilation#meshing-with-ghcs-2-stage-build this is one of two ways.

So, the only way to get a GHC bindist (for a recent GHC version) is to create it on real hardware (or an emulated VM, e.g. Qemu.)

I currently use QEMU...

If you got RISCV-V hardware, this shouldn't be much of an issue: Distributions like SuSE or Debian ship GHC with the LLVM backend configured. Though, be prepared that building and bundling with take about a day (without running the testsuite.)

...but HW is on its way.

As you likely want to ship only from trusted sources, [...]

No. I intend to cross-compile from either linux/amd64 or linux/arm64/v8 to linux/riscv64 using my Alpine-based GHC musl docker images.

So, I'd be excited to see a GHC/RISC-V Docker image (thanks a lot for bringing this up, BTW 👍 ), but we probably aren't ready, yet.

[benz0li]

[.................................] To cross-compile GHC itself, set TARGET: stage
1 will be a cross-compiler, and stage 2 will be the cross-compiled
GHC.

@supersven This seems to be the alternative.

But with my limited knowledge regarding GHC and cross-compiling¹, I am unable to derive the required steps for hadrian myself.

Footnotes

1. RISC-V GNU Compiler Toolchain: https://github.com/riscv-collab/riscv-gnu-toolchain ↩

[supersven]

@benz0li Ah, I see 💡

E.g. Debian Sid (GHC 9.4.7, https://packages.debian.org/sid/ghc) and Experimental (9.6.6, https://packages.debian.org/experimental/ghc) ship with RISC-V GHC. If you get one of these running in Qemu, you should be able to build a GHC bindist:

./boot && ./configure
hadrian/build -j --flavour=release binary-dist

I fear the documentation is a bit outdated. To my knowledge, building cross-compiled GHCs with Hadrian is a work-in-progress: https://gitlab.haskell.org/ghc/ghc/-/merge_requests/11444

[benz0li]

FYI @mpilgrem The quay.io/benz0li/ghc-musl:9.10.1-linux-riscv64 image also includes an unofficial and untested Linux/RISC-V build of Stack.

Both GHC and Stack are built (manually) from source on an emulated Linux/RISC-V platform.
👉 Since this takes a lot of time, linux/riscv64 images are released with a delay.