Re: [PATCH V6 0/3] Rust support for powerpc

From: Mukesh Kumar Chaurasiya

Date: Thu Mar 26 2026 - 18:17:38 EST

On Wed, Mar 25, 2026 at 01:59:55PM +0530, Madhavan Srinivasan wrote:
>
> On 2/10/26 2:30 PM, Mukesh Kumar Chaurasiya (IBM) wrote:
> > Enable experimental rust support for ppc64le and ppc32be. The patch for
> > ppc32 has been provided by Link Mauve[1] and ppc64le support[2] has been
> > merged over it. ppc32 needs some toolchain fixes mentioned in the patch
> > `rust: Add PowerPC support` and the discussion for that is done here[1].
> >
> > This has been tested on powernv9 hardware and power10 pseries qemu. I
> > I request Link to test the ppc32 part as i don't have a hardware to test
> > it out.
> >
> > [1] https://lore.kernel.org/all/20260204030507.8203-1-linkmauve@xxxxxxxxxxxx
> > [2] https://lore.kernel.org/all/20260204042417.83903-1-mkchauras@xxxxxxxxx
>
> Could see these build issues with the Rust patchset in the compilation of
> powerpc-next-test
> This happens when compilation happens only with few threads
>
> # rustc --version
> rustc 1.94.0 (4a4ef493e 2026-03-02)
>
> ....
> EXPORTS rust/exports_core_generated.h
> BINDGEN rust/bindings/bindings_generated.rs
> BINDGEN rust/bindings/bindings_helpers_generated.rs
> CC rust/helpers/helpers.o
> EXPORTS rust/exports_helpers_generated.h
> RUSTC L rust/compiler_builtins.o
> RUSTC L rust/ffi.o
> RUSTC PL rust/libproc_macro2.rlib
> error[E0464]: multiple candidates for `rmeta` dependency `core` found
> --> rust/proc-macro2/marker.rs:4:5
> |
> 4 | use core::marker::PhantomData;
> | ^^^^
> |
> = note: candidate #1: /root/.rustup/toolchains/nightly-powerpc64le-unknown-linux-gnu/lib/rustlib/powerpc64le-unknown-linux-gnu/lib/libcore-951759db375eea0c.rmeta
> = note: candidate #2: ./rust/libcore.rmeta
>
> error[E0119]: conflicting implementations of trait `PartialEq` for type
> `fallback::Ident`
> --> rust/proc-macro2/fallback.rs:875:1
> |
> 869 | impl PartialEq for Ident {
> | ------------------------ first implementation here
> ...
> 875 | / impl<T> PartialEq<T> for Ident
> 876 | | where
> 877 | | T: ?Sized + AsRef<str>,
> | |___________________________^ conflicting implementation for
> `fallback::Ident`
>
> error[E0277]: `LexError` doesn't implement `std::fmt::Display`
> --> rust/proc-macro2/lib.rs:347:16
> |
> 347 | impl Error for LexError {}
> | ^^^^^^^^ unsatisfied trait bound
> |
> help: the trait `std::fmt::Display` is not implemented for `LexError`
> --> rust/proc-macro2/lib.rs:204:1
> |
> 204 | pub struct LexError {
> | ^^^^^^^^^^^^^^^^^^^
> note: required by a bound in `std::error::Error`
> --> /root/.rustup/toolchains/nightly-powerpc64le-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/error.rs:59:26
> |
> 59 | pub trait Error: Debug + Display {
> | ^^^^^^^ required by this bound in `Error`
>
> error[E0277]: `LexError` doesn't implement `Debug`
> --> rust/proc-macro2/lib.rs:347:16
> |
> 347 | impl Error for LexError {}
> | ^^^^^^^^ unsatisfied trait bound
> |
> help: the trait `Debug` is not implemented for `LexError`
> --> rust/proc-macro2/lib.rs:204:1
> |
> 204 | pub struct LexError {
> | ^^^^^^^^^^^^^^^^^^^
> = note: add `#[derive(Debug)]` to `LexError` or manually `impl Debug for
> LexError`
> note: required by a bound in `std::error::Error`
> --> /root/.rustup/toolchains/nightly-powerpc64le-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/error.rs:59:18
> |
> 59 | pub trait Error: Debug + Display {
> | ^^^^^ required by this bound in `Error`
>
> error: aborting due to 4 previous errors
>
> ......
> But when parallelized with more threads (-j 128) compilation passes with out
> any error
> There is some ordering of libcore is messing up I guess (I could be wrong)
> (I have removed the warning of unstable features messages here for cleaner
> output)
>
> ....
> VDSO64SYM include/generated/vdso64-offsets.h
> RUSTC L rust/core.o
> BINDGEN rust/bindings/bindings_generated.rs
> BINDGEN rust/bindings/bindings_helpers_generated.rs
> CC rust/helpers/helpers.o
> RUSTC PL rust/libproc_macro2.rlib
> BINDGEN rust/uapi/uapi_generated.rs
> RSCPP rust/kernel/generated_arch_static_branch_asm.rs
> RSCPP rust/kernel/generated_arch_warn_asm.rs
> RSCPP rust/kernel/generated_arch_reachable_asm.rs
> clang diag: ./arch/powerpc/include/uapi/asm/ioctl.h:5:9: warning:
> '_IOC_SIZEBITS' macro redefined [-Wmacro-redefined]
> clang diag: ./arch/powerpc/include/uapi/asm/ioctl.h:6:9: warning:
> '_IOC_DIRBITS' macro redefined [-Wmacro-redefined]
> clang diag: ./arch/powerpc/include/uapi/asm/ioctl.h:8:9: warning:
> '_IOC_NONE' macro redefined [-Wmacro-redefined]
> clang diag: ./arch/powerpc/include/uapi/asm/ioctl.h:10:9: warning:
> '_IOC_WRITE' macro redefined [-Wmacro-redefined]
> EXPORTS rust/exports_helpers_generated.h
> RUSTC PL rust/libquote.rlib
> RUSTC PL rust/libsyn.rlib
> RUSTC P rust/libpin_init_internal.so
> RUSTC P rust/libmacros.so
> EXPORTS rust/exports_core_generated.h
> RUSTC L rust/compiler_builtins.o
> RUSTC L rust/ffi.o
> RUSTC L rust/pin_init.o
> RUSTC L rust/build_error.o
> RUSTC L rust/bindings.o
> RUSTC L rust/uapi.o
> EXPORTS rust/exports_bindings_generated.h
> RUSTC L rust/kernel.o
> EXPORTS rust/exports_kernel_generated.h
> LDS scripts/module.lds
> HOSTCC usr/gen_init_cpio
> CC init/main.o
> ....
>
> Also I see some errors when compiling modules. I am looking at these and any
> help is welcome.
> I will pull out Rust patches for now from powerpc-linux next-test branch and
> once this is
> restored I will add these patches back to branch for the merge.
>
> Maddy
>
Aah this happens because core.o is compiled before libproc_macro2.rlib
starts compiling. Once the core.o is compiled it generates the
libcore.rmeta, leading to conflict in two libcore.rmeta available.

I can think of 2 solutions here for this,

1. We can make the libproc_macro2.rlib libquote.rlib libsyn.rlib compile
befor the core.o is compiled OR
2. We can force these to use the toolchain core's metadata and not look
into the kernel's rust directory.

I am still not able to figure out why this is not happening for x86.

What should we do in this case?

Regards,
Mukesh

> > Changelog:
> > V5 -> V6:
> > - Added a missing Tested by from Venkat which got missed since V3
> > - Support is marked as Maintained instead of experimental
> > V5: https://lore.kernel.org/all/20260210053756.2088302-1-mkchauras@xxxxxxxxx
> >
> > V4 -> V5:
> > - Removed a nested ifdef from PPC64 for Little endian toolchain
> > V4: https://lore.kernel.org/all/20260209105456.1551677-1-mkchauras@xxxxxxxxx
> >
> > V3 -> V4:
> > - Co-developed-by header added in patch 1
> > V3: https://lore.kernel.org/all/20260205180429.3280657-1-mkchauras@xxxxxxxxx
> >
> > V2 -> V3:
> > - Splited HAVE_RUST in 2 lines
> > - BINDGEN_TARGET_powerpc initialized before assigning the same to
> > BINDGEN_TARGET
> > V2: https://lore.kernel.org/all/20260204210125.613350-1-mkchauras@xxxxxxxxx
> >
> > V1 -> V2:
> > - jump label fix for rust has been moved to a separate patch
> > - PPC32 support has been taken
> > - rust support has been marked experimental
> > - target.json dependency has been removed
> > - HAVE_RUST now depends on CPU_LITTLE_ENDIAN for PPC64
> >
> >
> > Link Mauve (1):
> > rust: Add PowerPC support
> >
> > Mukesh Kumar Chaurasiya (IBM) (2):
> > powerpc/jump_label: adjust inline asm to be consistent
> > powerpc: Enable Rust for ppc64le
> >
> > Documentation/rust/arch-support.rst | 1 +
> > arch/powerpc/Kconfig | 2 ++
> > arch/powerpc/Makefile | 7 +++++++
> > arch/powerpc/include/asm/jump_label.h | 23 +++++++++++++----------
> > rust/Makefile | 10 +++++++++-
> > 5 files changed, 32 insertions(+), 11 deletions(-)
> >