[PATCH 1/3] arm64: rust: Enable Rust support for AArch64

[Will Deacon]

On Wed, Jan 25, 2023 at 04:37:37PM +0000, Jamie Cunliffe wrote:
> From: Miguel Ojeda <ojeda at kernel.org>
> 
> This commit provides the build flags for Rust for AArch64. The core Rust
> support already in the kernel does the rest.
> 
> The Rust samples have been tested with this commit.
> 
> [jcunliffe: Arm specific parts taken from Miguel's upstream tree]
> 
> Signed-off-by: Miguel Ojeda <ojeda at kernel.org>
> Co-developed-by: Jamie Cunliffe <Jamie.Cunliffe at arm.com>
> Signed-off-by: Jamie Cunliffe <Jamie.Cunliffe at arm.com>
> ---
>  Documentation/rust/arch-support.rst |  1 +
>  arch/arm64/Kconfig                  |  1 +
>  scripts/generate_rust_target.rs     | 13 ++++++++++++-
>  3 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/rust/arch-support.rst b/Documentation/rust/arch-support.rst
> index 6982b63775da..3776059a385a 100644
> --- a/Documentation/rust/arch-support.rst
> +++ b/Documentation/rust/arch-support.rst
> @@ -15,5 +15,6 @@ support corresponds to ``S`` values in the ``MAINTAINERS`` file.
>  ============  ================  ==============================================
>  Architecture  Level of support  Constraints
>  ============  ================  ==============================================
> +``arm64``     Maintained        None.
>  ``x86``       Maintained        ``x86_64`` only.
>  ============  ================  ==============================================
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 03934808b2ed..fc3800e82802 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -209,6 +209,7 @@ config ARM64
>  	select HAVE_FUNCTION_ARG_ACCESS_API
>  	select MMU_GATHER_RCU_TABLE_FREE
>  	select HAVE_RSEQ
> +	select HAVE_RUST
>  	select HAVE_STACKPROTECTOR
>  	select HAVE_SYSCALL_TRACEPOINTS
>  	select HAVE_KPROBES
> diff --git a/scripts/generate_rust_target.rs b/scripts/generate_rust_target.rs
> index 3c6cbe2b278d..fe0e4ba54492 100644
> --- a/scripts/generate_rust_target.rs
> +++ b/scripts/generate_rust_target.rs
> @@ -148,7 +148,18 @@ 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") {
> +        ts.push("arch", "aarch64");
> +        ts.push(
> +            "data-layout",
> +            "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128",
> +        );
> +        ts.push("disable-redzone", true);
> +        ts.push("features", "+strict-align,+neon,+fp-armv8");
> +        ts.push("llvm-target", "aarch64-linux-gnu");
> +        ts.push("max-atomic-width", 128);
> +        ts.push("target-pointer-width", "64");

Why do we need to specify this stuff here? LLVM already knows about AArch64
and can compute the data-layout string in computeDataLayout(). Can we have
the tools figure this out for us instead, please?

Will