[PATCH v2 5/6] ARM: rust: Enable Rust support for ARMv4T

[Gary Guo]

On Thu Oct 8, 2026 at 7:37 AM CEST, Karl Mehltretter wrote:
> The armv5te target emits clz and blx, which ARMv4T lacks. Kernels that
> contain an ARMv4T CPU are excluded from Rust for that reason.
>
> Nothing else in the Rust code depends on ARMv5. Use rustc's
> armv4t-unknown-linux-gnueabi target for these kernels. Like the C code,
> the Rust code of a combined ARMv4T and ARMv5 kernel is then built for
> ARMv4T.
>
> ARMv4 (StrongARM, FA526) stays excluded. It has no bx and rustc has no
> target for it.
>
> Tested in QEMU sx1 (OMAP310, ARM925T) with omap1_defconfig. The Rust
> samples, all Rust KUnit suites and the doctests pass with the current
> and with the minimum tool versions.
>
> at91_dt_defconfig combines ARMv4T and ARMv5 and is built for ARMv4T.
> That kernel passes the same tests on a Microchip SAM9X75 Curiosity
> board (ARM926EJ-S).
>
> Assisted-by: LLM
> Signed-off-by: Karl Mehltretter <kmehltretter at gmail.com>
> ---
>  Documentation/rust/arch-support.rst | 8 ++++----
>  arch/arm/Kconfig                    | 2 +-
>  arch/arm/Makefile                   | 1 +
>  3 files changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/rust/arch-support.rst b/Documentation/rust/arch-support.rst
> index d6d1bef44c8f..3f39cf55b6f4 100644
> --- a/Documentation/rust/arch-support.rst
> +++ b/Documentation/rust/arch-support.rst
> @@ -12,15 +12,15 @@ which uses ``libclang``.
>  Below is a general summary of architectures that currently work. Level of
>  support corresponds to ``S`` values in the ``MAINTAINERS`` file.
>  
> -=============  ================  ==============================================
> +=============  ================  ======================================================
>  Architecture   Level of support  Constraints
> -=============  ================  ==============================================
> -``arm``        Maintained        ARMv5TE, ARMv6K and ARMv7, Little Endian only.
> +=============  ================  ======================================================
> +``arm``        Maintained        ARMv4T, ARMv5TE, ARMv6K and ARMv7, Little Endian only.

Can we say "ARMv4T or above" or something similar?

Best,
Gary

>  ``arm64``      Maintained        Little Endian only.
>  ``loongarch``  Maintained        \-
>  ``riscv``      Maintained        ``riscv64`` and LLVM/Clang only.
>  ``s390``       Maintained        ``CONFIG_EXPOLINE`` must be disabled.
>  ``um``         Maintained        \-
>  ``x86``        Maintained        ``x86_64`` only.
> -=============  ================  ==============================================
> +=============  ================  ======================================================