kbuild: rust: add rustc-min-version support function

commit ac95414 upstream.

Introduce `rustc-min-version` support function that mimics
`{gcc,clang}-min-version` ones, following commit 88b61e3
("Makefile.compiler: replace cc-ifversion with compiler-specific macros").

In addition, use it in the first use case we have in the kernel (which
was done independently to minimize the changes needed for the fix).

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Fiona Behrens <me@Kloenk.dev>
Reviewed-by: Nicolas Schier <n.schier@avm.de>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 1814e71a4e9c20bd69dbe1e007d31c0ab2c237a2)
Signed-off-by: Jack Vogel <jack.vogel@oracle.com>

Author: ojeda

Documentation/kbuild/makefiles.rst

@@ -656,6 +656,20 @@ cc-cross-prefix
             endif
     endif
 
+$(RUSTC) support functions
+--------------------------
+
+rustc-min-version
+  rustc-min-version tests if the value of $(CONFIG_RUSTC_VERSION) is greater
+  than or equal to the provided value and evaluates to y if so.
+
+  Example::
+
+    rustflags-$(call rustc-min-version, 108500) := -Cfoo
+
+  In this example, rustflags-y will be assigned the value -Cfoo if
+  $(CONFIG_RUSTC_VERSION) is >= 1.85.0.
+
 $(LD) support functions
 -----------------------
 

arch/arm64/Makefile

@@ -48,7 +48,7 @@ KBUILD_CFLAGS	+= $(CC_FLAGS_NO_FPU) \
 KBUILD_CFLAGS	+= $(call cc-disable-warning, psabi)
 KBUILD_AFLAGS	+= $(compat_vdso)
 
-ifeq ($(call test-ge, $(CONFIG_RUSTC_VERSION), 108500),y)
+ifeq ($(call rustc-min-version, 108500),y)
 KBUILD_RUSTFLAGS += --target=aarch64-unknown-none-softfloat
 else
 KBUILD_RUSTFLAGS += --target=aarch64-unknown-none -Ctarget-feature="-neon"

scripts/Makefile.compiler

@@ -67,6 +67,10 @@ gcc-min-version = $(call test-ge, $(CONFIG_GCC_VERSION), $1)
 # Usage: cflags-$(call clang-min-version, 110000) += -foo
 clang-min-version = $(call test-ge, $(CONFIG_CLANG_VERSION), $1)
 
+# rustc-min-version
+# Usage: rustc-$(call rustc-min-version, 108500) += -Cfoo
+rustc-min-version = $(call test-ge, $(CONFIG_RUSTC_VERSION), $1)
+
 # ld-option
 # Usage: KBUILD_LDFLAGS += $(call ld-option, -X, -Y)
 ld-option = $(call try-run, $(LD) $(KBUILD_LDFLAGS) $(1) -v,$(1),$(2),$(3))