Re: [PATCH v2] arm: rust: Enable Rust support for ARMv7

[Christian Schrefl]

Greetings,

Friendly Ping :)

This has been on the mailing list for quite some time with only a few responses.

Please let me know if something is needed from my side (like rebasing or wanted changes).

Cheers
Christian


On 17.06.24 6:03 PM, Christian Schrefl wrote:
> This commit allows building ARMv7 kernels with Rust support.
> 
> The rust core library expects some __eabi_... functions
> that are not implemented in the kernel.
> Those functions are some float operations and __aeabi_uldivmod.
> For now those are implemented with define_panicking_intrinsics!.
> 
> This is based on the code by Sven Van Asbroeck from the original
> rust branch and inspired by the AArch64 version by Jamie Cunliffe.
> 
> I have tested the rust samples and a custom simple MMIO module
> on hardware (De1SoC FPGA + Arm A9 CPU).
> 
> This only includes support for ARMv7, but supporting other
> sub-architectures in the future should be as simple as setting 
> the correct rustc target.
> 
> Signed-off-by: Christian Schrefl <chrisi.schrefl@xxxxxxxxx>
> ---
> Changes since V1 [1]:
> - Removed unrelated whitespace change.
> - Added target name to panic message in scripts/generate_rust_target.rs.
> - Fixed the comment in rust/bindgen_parameters.
> 
> 
> [1]: https://lore.kernel.org/rust-for-linux/4e0f5932-c7bc-4878-862c-1186cbecd71d@xxxxxxxxx 
> --
>  Documentation/rust/arch-support.rst |  1 +
>  arch/arm/Kconfig                    |  1 +
>  arch/arm/Makefile                   |  1 +
>  rust/Makefile                       |  8 ++++++++
>  rust/bindgen_parameters             |  4 ++++
>  rust/compiler_builtins.rs           | 24 ++++++++++++++++++++++++
>  scripts/generate_rust_target.rs     |  4 +++-
>  7 files changed, 42 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/rust/arch-support.rst b/Documentation/rust/arch-support.rst
> index b13e19d84744..4bf5205f526d 100644
> --- a/Documentation/rust/arch-support.rst
> +++ b/Documentation/rust/arch-support.rst
> @@ -15,6 +15,7 @@ support corresponds to ``S`` values in the ``MAINTAINERS`` file.
>  =============  ================  ==============================================
>  Architecture   Level of support  Constraints
>  =============  ================  ==============================================
> +``arm``        Maintained        ARMv7 Little Endian only.
>  ``arm64``      Maintained        Little Endian only.
>  ``loongarch``  Maintained        \-
>  ``riscv``      Maintained        ``riscv64`` only.
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index ee5115252aac..f07149fe078b 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -126,6 +126,7 @@ config ARM
>  	select MMU_GATHER_RCU_TABLE_FREE if SMP && ARM_LPAE
>  	select HAVE_REGS_AND_STACK_ACCESS_API
>  	select HAVE_RSEQ
> +	select HAVE_RUST if CPU_LITTLE_ENDIAN && CPU_32v7
>  	select HAVE_STACKPROTECTOR
>  	select HAVE_SYSCALL_TRACEPOINTS
>  	select HAVE_UID16
> diff --git a/arch/arm/Makefile b/arch/arm/Makefile
> index 71afdd98ddf2..9cc10e32e8be 100644
> --- a/arch/arm/Makefile
> +++ b/arch/arm/Makefile
> @@ -150,6 +150,7 @@ endif
>  KBUILD_CPPFLAGS	+=$(cpp-y)
>  KBUILD_CFLAGS	+=$(CFLAGS_ABI) $(CFLAGS_ISA) $(arch-y) $(tune-y) $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,)) -msoft-float -Uarm
>  KBUILD_AFLAGS	+=$(CFLAGS_ABI) $(AFLAGS_ISA) -Wa,$(arch-y) $(tune-y) -include asm/unified.h -msoft-float
> +KBUILD_RUSTFLAGS += --target=arm-unknown-linux-gnueabi
>  
>  CHECKFLAGS	+= -D__arm__
>  
> diff --git a/rust/Makefile b/rust/Makefile
> index f70d5e244fee..8214a6f378e3 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -287,6 +287,7 @@ bindgen_skip_c_flags := -mno-fp-ret-in-387 -mpreferred-stack-boundary=% \
>  # Derived from `scripts/Makefile.clang`.
>  BINDGEN_TARGET_x86	:= x86_64-linux-gnu
>  BINDGEN_TARGET_arm64	:= aarch64-linux-gnu
> +BINDGEN_TARGET_arm	:= arm-linux-gnueabi
>  BINDGEN_TARGET		:= $(BINDGEN_TARGET_$(SRCARCH))
>  
>  # All warnings are inhibited since GCC builds are very experimental,
> @@ -413,6 +414,13 @@ redirect-intrinsics = \
>  	__muloti4 __multi3 \
>  	__udivmodti4 __udivti3 __umodti3
>  
> +ifdef CONFIG_ARM
> +	# Add eabi initrinsics for ARM 32-bit
> +	redirect-intrinsics += \
> +		__aeabi_fadd __aeabi_fmul __aeabi_fcmpeq __aeabi_fcmple __aeabi_fcmplt __aeabi_fcmpun \
> +		__aeabi_dadd __aeabi_dmul __aeabi_dcmple __aeabi_dcmplt __aeabi_dcmpun \
> +		__aeabi_uldivmod
> +endif
>  ifneq ($(or $(CONFIG_ARM64),$(and $(CONFIG_RISCV),$(CONFIG_64BIT))),)
>  	# These intrinsics are defined for ARM64 and RISCV64
>  	redirect-intrinsics += \
> diff --git a/rust/bindgen_parameters b/rust/bindgen_parameters
> index a721d466bee4..83f28ae4bb2b 100644
> --- a/rust/bindgen_parameters
> +++ b/rust/bindgen_parameters
> @@ -24,3 +24,7 @@
>  # These functions use the `__preserve_most` calling convention, which neither bindgen
>  # nor Rust currently understand, and which Clang currently declares to be unstable.
>  --blocklist-function __list_.*_report
> +
> +# Depending on how the architecture defines `ARCH_SLAB_MINALIGN`, `bindgen` might generate a binding.
> +# Disable this here as there is a `const` item that will always be generated in `bindings_helper.h`
> +--blocklist-item ARCH_SLAB_MINALIGN
> diff --git a/rust/compiler_builtins.rs b/rust/compiler_builtins.rs
> index bba2922c6ef7..c37142b16a45 100644
> --- a/rust/compiler_builtins.rs
> +++ b/rust/compiler_builtins.rs
> @@ -70,5 +70,29 @@ pub extern "C" fn $ident() {
>      __umodti3,
>  });
>  
> +#[cfg(target_arch = "arm")]
> +define_panicking_intrinsics!("`f32` should not be used", {
> +    __aeabi_fadd,
> +    __aeabi_fmul,
> +    __aeabi_fcmpeq,
> +    __aeabi_fcmple,
> +    __aeabi_fcmplt,
> +    __aeabi_fcmpun,
> +});
> +
> +#[cfg(target_arch = "arm")]
> +define_panicking_intrinsics!("`f64` should not be used", {
> +    __aeabi_dadd,
> +    __aeabi_dmul,
> +    __aeabi_dcmple,
> +    __aeabi_dcmplt,
> +    __aeabi_dcmpun,
> +});
> +
> +#[cfg(target_arch = "arm")]
> +define_panicking_intrinsics!("`u64` division/modulo should not be used", {
> +    __aeabi_uldivmod,
> +});
> +
>  // NOTE: if you are adding a new intrinsic here, you should also add it to
>  // `redirect-intrinsics` in `rust/Makefile`.
> diff --git a/scripts/generate_rust_target.rs b/scripts/generate_rust_target.rs
> index 641b713a033a..c3a6058fdf30 100644
> --- a/scripts/generate_rust_target.rs
> +++ b/scripts/generate_rust_target.rs
> @@ -148,7 +148,9 @@ fn main() {
>      let mut ts = TargetSpec::new();
>  
>      // `llvm-target`s are taken from `scripts/Makefile.clang`.
> -    if cfg.has("ARM64") {
> +    if cfg.has("ARM") {
> +        panic!("arm uses the builtin rustc arm-unknown-linux-gnueabi target");
> +    } else if cfg.has("ARM64") {
>          panic!("arm64 uses the builtin rustc aarch64-unknown-none target");
>      } else if cfg.has("RISCV") {
>          if cfg.has("64BIT") {
> 
> base-commit: 1613e604df0cd359cf2a7fbd9be7a0bcfacfabd0