Support powerpc

[alex]

PowerPC 64-bits little-endian is supported by Ubuntu, Red Hat and Debian, which means we should eventually support the ppc64el architecture.

Linux powerpc targets with official Ubuntu binutils etc. support:

Linux arch  QEMU target     LLVM target  Ubuntu binutils                 Example Rust triple
----------  --------------  -----------  ------------------------------  -------------------

powerpc     ppc-softmmu     PowerPC      binutils-powerpc-linux-gnu      powerpc-unknown-linux-gnu
powerpc     ppc64-softmmu   PowerPC      binutils-powerpc64le-linux-gnu  powerpc64-unknown-linux-gnu

[alex]

These platforms selected because they're also well supported by Rust-for-LLVM.

Which leads me to a question... both MIPS and PPC come in BE and LE variants, does anyone know off hand which the kernel implements (or both?)? /cc @nickdesaulniers

[ojeda]

Both, although little-endian are the important one (e.g. ppc64el is supported by Ubuntu and Red Hat, mipsel and mips64el by Debian).

Let me split the arches into issues, I will also create the s390x and add a couple details that may help.

[alex]

Sounds good, thanks!

On Sun, Mar 14, 2021 at 3:12 PM Miguel Ojeda @.***> wrote:

Both, although little-endian are the important one (e.g. ppc64el is supported by Ubuntu and Red Hat, mipsel and mips64el by Debian).

Let me split the arches into issues, I will also create the s390x and add a couple details that may help.

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[alex]

Patchset for ppc64le was sent to the mailing list.

[ojeda]

Link: https://lore.kernel.org/rust-for-linux/20210323032624.1039422-1-mpe@ellerman.id.au/

[alex]

Basic support landed -- we should add this to the documentation and close this issue.

[ojeda]

We could keep this open, at least until we get "most" of the ppc support in place (e.g. the rest of the CI, GCC or not, etc.).

[jhamby]

I'm interested in testing ppc64 big-endian mode on my PowerMac quad G5, which is missing little-endian support at the CPU level. I've been working to add features to the KVM module for the usermode emulation (the G5 also lacks the hypervisor added in POWER7, so it only runs the KVM-PR module, not KVM-HV).

I like how the ppc C code is written to be correct whether built for 32-bit or 64-bit, big-endian or little-endian, and 4K or 64K page sizes, based on preprocessor defines. You already have PAGE_SIZE and byte order support in Rust, and types that map to long and ulong. If you can write conditional code based on whether CONFIG_64BIT is set in the kernel config, there shouldn't be any problems getting all eight combinations working on ppc. I've had good luck so far with Rust itself on ppc64 BE.