[PATCH v4 2/2] arm64: rust: Enable Rust support for AArch64

[Behme Dirk (CM/ESO2)]

On 20.10.2023 17:50, Jamie Cunliffe wrote:
> This commit provides the build flags for Rust for AArch64. The core Rust
> support already in the kernel does the rest. This enables the PAC ret
> and BTI options in the Rust build flags to match the options that are
> used when building C.
> 
> The Rust samples have been tested with this commit.
> 
> Signed-off-by: Jamie Cunliffe <Jamie.Cunliffe at arm.com>
> Acked-by: Will Deacon <will at kernel.org>


I'm using it since some weeks cross compiling from x86. Boots executing 
the sample code and the KUnit doctests. So:

Tested-by: Dirk Behme <dirk.behme at de.bosch.com>

Would be nice if we could get this merged :)

Dirk


> ---
>   Documentation/rust/arch-support.rst | 1 +
>   arch/arm64/Kconfig                  | 1 +
>   arch/arm64/Makefile                 | 4 ++++
>   rust/Makefile                       | 1 +
>   scripts/generate_rust_target.rs     | 4 +++-
>   5 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/rust/arch-support.rst b/Documentation/rust/arch-support.rst
> index b91e9ef4d0c2..6bcb3b97c5b6 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
>   ============  ================  ==============================================
> +``arm64``     Maintained        Little Endian only.
>   ``um``        Maintained        ``x86_64`` only.
>   ``x86``       Maintained        ``x86_64`` only.
>   ============  ================  ==============================================
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 78f20e632712..d72618433521 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -227,6 +227,7 @@ config ARM64
>   	select HAVE_FUNCTION_ARG_ACCESS_API
>   	select MMU_GATHER_RCU_TABLE_FREE
>   	select HAVE_RSEQ
> +	select HAVE_RUST if CPU_LITTLE_ENDIAN
>   	select HAVE_STACKPROTECTOR
>   	select HAVE_SYSCALL_TRACEPOINTS
>   	select HAVE_KPROBES
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 2d49aea0ff67..52d75c9483a9 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -41,6 +41,8 @@ KBUILD_CFLAGS	+= -mgeneral-regs-only	\
>   KBUILD_CFLAGS	+= $(call cc-disable-warning, psabi)
>   KBUILD_AFLAGS	+= $(compat_vdso)
>   
> +KBUILD_RUSTFLAGS += --target=aarch64-unknown-none -Ctarget-feature="-neon"
> +
>   KBUILD_CFLAGS	+= $(call cc-option,-mabi=lp64)
>   KBUILD_AFLAGS	+= $(call cc-option,-mabi=lp64)
>   
> @@ -65,7 +67,9 @@ endif
>   
>   ifeq ($(CONFIG_ARM64_BTI_KERNEL),y)
>     KBUILD_CFLAGS += -mbranch-protection=pac-ret+bti
> +  KBUILD_RUSTFLAGS += -Zbranch-protection=bti,pac-ret
>   else ifeq ($(CONFIG_ARM64_PTR_AUTH_KERNEL),y)
> +  KBUILD_RUSTFLAGS += -Zbranch-protection=pac-ret
>     ifeq ($(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET),y)
>       KBUILD_CFLAGS += -mbranch-protection=pac-ret
>     else
> diff --git a/rust/Makefile b/rust/Makefile
> index 8d75a6ffe951..8ced65c9b905 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -294,6 +294,7 @@ 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		:= $(BINDGEN_TARGET_$(SRCARCH))
>   
>   # All warnings are inhibited since GCC builds are very experimental,
> diff --git a/scripts/generate_rust_target.rs b/scripts/generate_rust_target.rs
> index 3c6cbe2b278d..ec5ef35dbe52 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("X86_64") {
> +    if cfg.has("ARM64") {
> +        panic!("arm64 uses the builtin rustc aarch64-unknown-none target");
> +    } else if cfg.has("X86_64") {
>           ts.push("arch", "x86_64");
>           ts.push(
>               "data-layout",