Architecture support (tracking issue)

[geofft]

Rust supported architectures: https://forge.rust-lang.org/platform-support.html For our purposes, we don't care much about Tier 1 vs. Tier 2, and even Tier 3 support is probably fine.

Another useful reference is Debian's arch status as of February 2018: https://alioth-lists.debian.net/pipermail/pkg-rust-maintainers/2018-February/001215.html (doesn't include all the arches the kernel supports)

arch	description	LLVM status	Rust status
alpha	DEC Alpha	removed from LLVM in 2011
arc	Synopsys ARC	present	needs port
arm	ARM 32-bit	present	ARMv5 and up is Tier 2
arm64	ARM 64-bit aka AARCH64	present	Tier 2
c6x	TI C6000-series VLIW DSPs	no LLVM port
csky	C-Sky	no LLVM port
h8300	Hitachi H8	no LLVM port
hexagon	Qualcomm Hexagon DSP, part of Snapdragon SoCs	present	added July 2019
ia64	Intel Itanium	removed from LLVM in 2009
m68k	Motorola 680x0	port exists, proposed for merge	work in progress
microblaze	Xilinx MicroBlaze for FPGAs	removed from LLVM
mips	MIPS (R3000 / MIPS I and up)	present for R4000 / MIPS II and up	Tier 2
nds32	Andes AndeStar 32-bit	proposed for merge in 2017	needs port
nios2	Altera Nios II for FPGAs	removed from LLVM in January 2019
openrisc	OpenRISC	out-of-tree backend	needs port
parisc	Hewlett-Packard PA-RISC aka hppa	no LLVM port
powerpc	PowerPC / POWER 32-bit, 64-bit LE, 64-bit BE	all present	all Tier 2
riscv	RISC-V	present	Tier 2
s390	z/Architecture 64-bit aka s390x	present	Tier 2
sh	Hitachi SuperH / J2	experimental out-of-tree backend	needs port
sparc	Sun SPARC 32- and 64-bit	present	Tier 2 for 64-bit (SPARC v9), needs 32-bit port
um	User-Mode Linux (on any userspace arch)	N/A	might just work?
x86	Intel x86 aka i386 and x86-64 aka amd64	present	Tier 1
xtensa	Tensilica Xtensa, used on ESP microcontrollers	proposed for merge in March 2019	work in progress

Re ARMv4 - the linked issue implies ARMv4 is only a microcontroller for OS-less use, but arch/arm/mach-gemini/ looks like an actual Linux target for ARMv4. There are also a few ARMv4T boards (i.e., with Thumb support). It looks like LLVM wants to emit BLX instructions which switch to Thumb mode, so unclear if plain ARMv4 will work. (Though forcing it to emit non-Thumb code only doesn't sound like it should be too difficult....)

Re MIPS I - see simias/psx-sdk-rs#1. MIPS I has load delay slots, LLVM's codegen would need to be taught about it. https://github.com/impiaaa/llvm-project seems to have a patch.

Some possible approaches for merging into mainline and dealing with architectures with no LLVM support and no realistic plans (e.g., processors no longer manufactured):

• Convince Linux to drop them <_< >_>
• Only support certain architectures via Kconfig - it's probably okay to only support some modules on the major architectures
• Use mrustc to compile via C https://github.com/thepowersgang/mrustc
• Use the LLVM C backend to compile via C #111
• Write a GCC frontend for Rust, see https://github.com/sapir/gcc-rust/tree/rust (which glues actual rustc into GCC) or https://github.com/redbrain/gccrs, both of which seem to be actively developed
• Something involving Cranelift, maybe? I don't have a good sense of what this would look like / whether it would work.

[XVilka]

Note, Hexagon was added in the Rust compiler: https://github.com/rust-lang/rust/pull/62814 So might me just worth testing the support.

[androm3da]

Note, Hexagon was added in the Rust compiler: rust-lang/rust#62814 So might me just worth testing the support.

My work to get hexagon-linux support for rust is incomplete, I still have to work out changes to libc and possibly more beyond that.

But the good news is that codegen support for the hexagon processor in general has been present in the compiler for a while. My recent changes were only for making userspace binaries. AFAIK the codegen support that was added by @michaelwu (around https://github.com/rust-lang/rust/pull/41524) should suffice for kernel module development.

[geofft]

Unicore has been removed in torvalds/linux@05119217a9bd199c4b8b12c01f86df09108b109b.

[geofft]

@nickdesaulniers says arc, hexagon, riscv, s390, and sparc are currently broken in ClangBuiltLinux CI (although support exists). I wonder if the breakage would affect Rust.

[sanxiyn]

C-SKY LLVM port got proposed in August 2020.

[nindalf]

Convince Linux to drop them << >>

Removing support for some of these architectures from the Linux Kernel is currently being discussed - Old platforms: bring out your dead