kbuild: rust: add CONFIG_RUSTC_LLVM_VERSION

Each version of Rust supports a range of LLVM versions. There are cases where
we want to gate a config on the LLVM version instead of the Rust version.
Normalized cfi integer tags are one example [1].

For consistency with cc-version and ld-version, the new version number is added
to the existing rustc-version script, rather than being added to a new script.

The invocation of rustc-version is being moved from init/Kconfig to
scripts/Kconfig.include to avoid invoking rustc-version.sh twice and for
consistency with cc-version.

Link: https://lore.kernel.org/all/[email protected]/ [1]
Signed-off-by: Gary Guo <[email protected]>
Signed-off-by: Alice Ryhl <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Miguel Ojeda <[email protected]>

Author: nbdd0121

init/Kconfig

@@ -62,7 +62,7 @@ config LLD_VERSION
 
 config RUSTC_VERSION
 	int
-	default $(shell,$(srctree)/scripts/rustc-version.sh $(RUSTC))
+	default $(rustc-version)
 	help
 	  It does not depend on `RUST` since that one may need to use the version
 	  in a `depends on`.
@@ -78,6 +78,10 @@ config RUST_IS_AVAILABLE
 	  In particular, the Makefile target 'rustavailable' is useful to check
 	  why the Rust toolchain is not being detected.
 
+config RUSTC_LLVM_VERSION
+	int
+	default $(rustc-llvm-version)
+
 config CC_CAN_LINK
 	bool
 	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(m64-flag)) if 64BIT

scripts/Kconfig.include

@@ -65,6 +65,10 @@ cc-option-bit = $(if-success,$(CC) -Werror $(1) -E -x c /dev/null -o /dev/null,$
 m32-flag := $(cc-option-bit,-m32)
 m64-flag := $(cc-option-bit,-m64)
 
+rustc-info := $(shell,$(srctree)/scripts/rustc-version.sh $(RUSTC))
+rustc-version := $(shell,set -- $(rustc-info) && echo $1)
+rustc-llvm-version := $(shell,set -- $(rustc-info) && echo $2)
+
 # $(rustc-option,<flag>)
 # Return y if the Rust compiler supports <flag>, n otherwise
 # Calls to this should be guarded so that they are not evaluated if

scripts/rustc-version.sh

@@ -3,14 +3,23 @@
 #
 # Usage: $ ./rustc-version.sh rustc
 #
-# Print the Rust compiler version in a 6 or 7-digit form.
+# Print the Rust compiler version and the LLVM version it uses in a 6 or
+# 7-digit form.
+
+# Convert the version string x.y.z to a canonical up-to-6-digits form.
+get_llvm_canonical_version()
+{
+	IFS=.
+	set -- $1
+	echo $((10000 * $1 + 100 * $2 + $3))
+}
 
 # Convert the version string x.y.z to a canonical up-to-7-digits form.
 #
-# Note that this function uses one more digit (compared to other
-# instances in other version scripts) to give a bit more space to
+# Note that this function uses one more digit (compared to other instances in
+# other version scripts and the instance above) to give a bit more space to
 # `rustc` since it will reach 1.100.0 in late 2026.
-get_canonical_version()
+get_rustc_canonical_version()
 {
 	IFS=.
 	set -- $1
@@ -19,8 +28,18 @@ get_canonical_version()
 
 if output=$("$@" --version 2>/dev/null); then
 	set -- $output
-	get_canonical_version $2
+	rustc_version=$(get_rustc_canonical_version $2)
 else
-	echo 0
+	echo 0 0
 	exit 1
 fi
+
+if output=$("$@" --version --verbose 2>/dev/null | grep LLVM); then
+	set -- $output
+	rustc_llvm_version=$(get_llvm_canonical_version $3)
+else
+	echo 0 0
+	exit 1
+fi
+
+echo $rustc_version $rustc_llvm_version