Add powerpc64le Linux support

[xingxue-ibm]

This PR adds support for powerpc64le Linux.

I'm not very familiar with Valgrind, so it’s currently unsupported on powerpc64 in this implementation. Any insights or guidance would be greatly appreciated.

Note: the test has dependency on the ucontext_t structure from the libc crate. PR Add ucontext_t and {get,set,make,swap}context for powerpc64-linux (cont.) has been approved but not yet included in the libc stable branch and release yet.

[Amanieu]

I did some testing on powerpc64 qemu (with 2b4700e to add the missing ucontext support). Currently this seems to crash even on the base smoke tests. The issue seems to be that function pointers on powerpc actually point to a 3-word descriptor with pc, r2 and r11 values. See https://rust.godbolt.org/z/c9enqqej7 for an example.

This is an initial review, I will do a more in-depth one once the initial problems are fixed.

[xingxue-ibm]

I did some testing on powerpc64 qemu (with 2b4700e to add the missing ucontext support). Currently this seems to crash even on the base smoke tests. The issue seems to be that function pointers on powerpc actually point to a 3-word descriptor with pc, r2 and r11 values. See https://rust.godbolt.org/z/c9enqqej7 for an example.

This is an initial review, I will do a more in-depth one once the initial problems are fixed.

Thanks for the review, @Amanieu! From the Compiler Explorer session (https://rust.godbolt.org/z/c9enqqej7, it looks like you compiled with --target powerpc64-unknown-linux-gnu, which is for big-endian. The implementation in this PR is intended for little-endian Linux systems such as Red Hat (--target powerpc64le-unknown-linux-gnu). I apologize for the confusion - I should have used powerpc64le in the title and description instead of powerpc64. (The compiler somehow complained about powerpc64le, but the implementation works with target_arch = "powerpc64").

warning: unexpected `cfg` condition value: `powerpc64le`
   --> src/lib.rs:239:13
    |
239 | #![cfg_attr(target_arch = "powerpc64le", feature(asm_experimental_arch))]
    |             ^^^^^^^^^^^^^^-------------
    |                           |
    |                           help: there is a expected value with a similar name: `"powerpc64"`
    |
    = note: expected values for `target_arch` are: `aarch64`, `amdgpu`, `arm`, `arm64ec`, `avr`, `bpf`, `csky`, `hexagon`, `loongarch32`, `loongarch64`, `m68k`, `mips`, `mips32r6`, `mips64`, `mips64r6`, `msp430`, `nvptx64`, `powerpc`, `powerpc64`, `riscv32`, `riscv64`, `s390x`, `sparc`, `sparc64`, `wasm32`, `wasm64`, `x86`, `x86_64`, and `xtensa`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default

The implementation runs 16 out of 21 unit tests successfully on RedHat.

$ cat /etc/redhat-release
Red Hat Enterprise Linux release 8.10 (Ootpa)
$ rustc --version --verbose
rustc 1.92.0-nightly (839222065 2025-10-05)
binary: rustc
commit-hash: 839222065a44ac21c15df68ed2f2f3c0127b0b8e
commit-date: 2025-10-05
host: powerpc64le-unknown-linux-gnu
release: 1.92.0-nightly
LLVM version: 21.1.2
$ cargo test
   Compiling corosensei v0.3.0 (/home/xingxue/corosensei.1)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 1.60s
     Running unittests src/lib.rs (target/debug/deps/corosensei-db2e5dad2186f5df)

running 21 tests
test tests::coroutine::backtrace_traces_to_host ... ignored
test stack::assert_send_sync ... ok
test tests::coroutine::stack_overflow ... ignored
test tests::coroutine::smoke ... ok
test tests::coroutine::stateful ... ok
test tests::coroutine::backward_stack_address - should panic ... ok
test tests::coroutine::trap_handler ... ignored
test tests::coroutine::trap_handler_panic ... ignored
test tests::on_stack::backtrace_traces_to_host ... ignored
test tests::coroutine::panics_propagated - should panic ... ok
test tests::coroutine::force_unwind ... ok
test tests::coroutine::forward_stack_address - should panic ... ok
test tests::coroutine::suspend_and_resume ... ok
test tests::coroutine::panics_propagated_via_parent - should panic ... ok
test tests::coroutine::stack_growth ... ok
test tests::on_stack::smoke ... ok
test tests::coroutine::suspend_and_resume_values ... ok
test tests::on_stack::stack_growth ... ok
test tests::on_stack::backward_stack_address - should panic ... ok
test tests::on_stack::forward_stack_address - should panic ... ok
test tests::on_stack::panics_propagated - should panic ... ok

test result: ok. 16 passed; 0 failed; 5 ignored; 0 measured; 0 filtered out; finished in 0.00s

   Doc-tests corosensei

running 6 tests
test src/coroutine.rs - coroutine::Coroutine::marker2 (line 111) - compile fail ... ok
test src/arch/powerpc64.rs - arch::powerpc64::TrapHandlerRegs (line 632) ... ok
test src/scoped.rs - scoped::ScopedCoroutine (line 70) ... ok
test src/lib.rs - (line 9) ... ok
test src/lib.rs - (line 93) ... ok
test src/lib.rs - (line 146) ... ok

test result: ok. 6 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 1.51s

$

[Amanieu]

I see, powerpc64 uses the ELFv1 ABI while powerc64le uses the ELFv2 ABI. You should be able to explicitly handle these with rust-lang/rust#142321. Although for now if might be ok to just compiler_error! on ELFv1 since it's not a supported ABI. We look into supporting it later.

[Amanieu]

Right, disregard my previous comments on the stack layout, I need to re-read the ABI document in detail.

[Amanieu]

I've tried to clean up the stack layout for the coroutine here: a783805

Let me know if you think this will work or if I missed anything.

[xingxue-ibm]

I've updated the stack layout as you suggested. Thank you!

[Amanieu]

I spent a few days reworking the code and optimizing the stack layout. This now passes all the tests.

Thanks a lot for pushing this forward! The only missing step before this can be merged is that we need a new release of the libc crate that includes the ucontext definition for PPC.

[Amanieu]

Also I would appreciate if you reviewed my changes to ensure I didn't miss anything.

[Amanieu]

Also note that since rust-lang/rust#148492, r29 no longer needs to be saved and can just be declared as a clobber.

[xingxue-ibm]

The changes look great, thank you so much! I really appreciate it!

[xingxue-ibm]

The dependent PR that adds ucontext_t for PowerPC64 Linux is included in the new libc crate release 0.2.178.

[xingxue-ibm]

Thank you very much, @Amanieu! This patch wouldn’t have been in such great shape without your help and guidance.