[PATCH] kbuild: rust: add `CONFIG_RUSTC_LLVM_VERSION`

[Gary Guo]

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].

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

Link: https://lore.kernel.org/all/20240925-cfi-norm-kasan-fix-v1-1-0328985cdf33@xxxxxxxxxx/ [1]
Signed-off-by: Gary Guo <gary@xxxxxxxxxxx>
---
 init/Kconfig                  |  6 +++++-
 scripts/Kconfig.include       |  3 +++
 scripts/rustc-llvm-version.sh | 22 ++++++++++++++++++++++
 3 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100755 scripts/rustc-llvm-version.sh

diff --git a/init/Kconfig b/init/Kconfig
index fbd0cb06a50a..304e2bd32bfd 100644
--- a/init/Kconfig
+++ b/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
diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
index 785a491e5996..33193ca6e803 100644
--- a/scripts/Kconfig.include
+++ b/scripts/Kconfig.include
@@ -65,6 +65,9 @@ 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-version := $(shell,$(srctree)/scripts/rustc-version.sh $(RUSTC))
+rustc-llvm-version := $(shell,$(srctree)/scripts/rustc-llvm-version.sh $(RUSTC))
+
 # $(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
diff --git a/scripts/rustc-llvm-version.sh b/scripts/rustc-llvm-version.sh
new file mode 100755
index 000000000000..b8ffa24afea8
--- /dev/null
+++ b/scripts/rustc-llvm-version.sh
@@ -0,0 +1,22 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Usage: $ ./rustc-version.sh rustc
+#
+# Print the LLVM version that the Rust compiler uses in a 6 digit form.
+
+# Convert the version string x.y.z to a canonical up-to-6-digits form.
+get_canonical_version()
+{
+	IFS=.
+	set -- $1
+	echo $((10000 * $1 + 100 * $2 + $3))
+}
+
+if output=$("$@" --version --verbose 2>/dev/null | grep LLVM); then
+	set -- $output
+	get_canonical_version $3
+else
+	echo 0
+	exit 1
+fi

base-commit: f5e50614e39e74401b492a2fa125f2e2b6458bab
-- 
2.44.1