[PATCH v4 1/2] rust: Refactor the build target to allow the use of builtin targets

[Catalin Marinas]

On Fri, Oct 20, 2023 at 04:50:55PM +0100, Jamie Cunliffe wrote:
> Eventually we want all architectures to be using the target as defined
> by rustc. However currently some architectures can't do that and are
> using the target.json specification. This puts in place the foundation
> to allow the use of the builtin target definition or a target.json
> specification.
> 
> Signed-off-by: Jamie Cunliffe <Jamie.Cunliffe at arm.com>
> ---
>  Makefile          | 1 -
>  arch/x86/Makefile | 1 +
>  rust/Makefile     | 5 ++++-
>  scripts/Makefile  | 4 +++-
>  4 files changed, 8 insertions(+), 3 deletions(-)

Adding the x86 maintainers - no functional change for x86, any objection
to this patch going in via the arm64 tree (part of the two-patch series
enabling Rust for arm64)?

Thanks.

(keeping the rest of the patch below for your reference)

> diff --git a/Makefile b/Makefile
> index 88ebf6547964..23100f193da3 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -566,7 +566,6 @@ KBUILD_CFLAGS += -fno-strict-aliasing
>  
>  KBUILD_CPPFLAGS := -D__KERNEL__
>  KBUILD_RUSTFLAGS := $(rust_common_flags) \
> -		    --target=$(objtree)/scripts/target.json \
>  		    -Cpanic=abort -Cembed-bitcode=n -Clto=n \
>  		    -Cforce-unwind-tables=n -Ccodegen-units=1 \
>  		    -Csymbol-mangling-version=v0 \
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 5bfe5caaa444..0f339d4abd40 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -68,6 +68,7 @@ export BITS
>  #    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383
>  #
>  KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx
> +KBUILD_RUSTFLAGS += --target=$(objtree)/scripts/target.json
>  KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2
>  
>  ifeq ($(CONFIG_X86_KERNEL_IBT),y)
> diff --git a/rust/Makefile b/rust/Makefile
> index 87958e864be0..8d75a6ffe951 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -428,8 +428,11 @@ $(obj)/core.o: private skip_clippy = 1
>  $(obj)/core.o: private skip_flags = -Dunreachable_pub
>  $(obj)/core.o: private rustc_objcopy = $(foreach sym,$(redirect-intrinsics),--redefine-sym $(sym)=__rust$(sym))
>  $(obj)/core.o: private rustc_target_flags = $(core-cfgs)
> -$(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs scripts/target.json FORCE
> +$(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs FORCE
>  	$(call if_changed_dep,rustc_library)
> +ifdef CONFIG_X86_64
> +$(obj)/core.o: scripts/target.json
> +endif
>  
>  $(obj)/compiler_builtins.o: private rustc_objcopy = -w -W '__*'
>  $(obj)/compiler_builtins.o: $(src)/compiler_builtins.rs $(obj)/core.o FORCE
> diff --git a/scripts/Makefile b/scripts/Makefile
> index 576cf64be667..c85d130a4125 100644
> --- a/scripts/Makefile
> +++ b/scripts/Makefile
> @@ -11,12 +11,14 @@ hostprogs-always-$(CONFIG_MODULE_SIG_FORMAT)		+= sign-file
>  hostprogs-always-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE)	+= insert-sys-cert
>  hostprogs-always-$(CONFIG_RUST_KERNEL_DOCTESTS)		+= rustdoc_test_builder
>  hostprogs-always-$(CONFIG_RUST_KERNEL_DOCTESTS)		+= rustdoc_test_gen
> -always-$(CONFIG_RUST)					+= target.json
>  
> +ifdef CONFIG_X86_64
> +always-$(CONFIG_RUST)					+= target.json
>  filechk_rust_target = $< < include/config/auto.conf
>  
>  $(obj)/target.json: scripts/generate_rust_target include/config/auto.conf FORCE
>  	$(call filechk,rust_target)
> +endif
>  
>  hostprogs += generate_rust_target
>  generate_rust_target-rust := y
> -- 
> 2.30.2