kbuild: rust: add `CONFIG_RUSTC_VERSION`

Now that we support several Rust versions, introduce
`CONFIG_RUSTC_VERSION` so that it can be used in Kconfig to enable and
disable configuration options based on the `rustc` version.

The approach taken resembles `pahole`'s -- see commit 613fe1692377
("kbuild: Add CONFIG_PAHOLE_VERSION"), i.e. a simple version parsing
without trying to identify several kinds of compilers, since so far
there is only one (`rustc`).

However, unlike `pahole`'s, we also print a zero if executing failed for
any reason, rather than checking if the command is found and executable
(which still leaves things like a file that exists and is executable,
but e.g. is built for another platform [1]). An equivalent approach to
the one here was also submitted for `pahole` [2].

Link: https://lore.kernel.org/rust-for-linux/CANiq72=4vX_tJMJLE6e+bg7ZECHkS-AQpm8GBzuK75G1EB7+Nw@mail.gmail.com/
Link: https://lore.kernel.org/linux-kbuild/20240728125527.690726-1-ojeda@kernel.org/
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Tested-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20240902165535.1101978-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

diff --git a/init/Kconfig b/init/Kconfig
index 839c83034006520a55ffd5d163c358aa22028c1a..38c1cfcce821e4c768acbe60d0db31d87533ca46 100644 (file)
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -60,6 +60,13 @@ config LLD_VERSION
        default $(ld-version) if LD_IS_LLD
        default 0
 
+config RUSTC_VERSION
+       int
+       default $(shell,$(srctree)/scripts/rustc-version.sh $(RUSTC))
+       help
+         It does not depend on `RUST` since that one may need to use the version
+         in a `depends on`.
+
 config RUST_IS_AVAILABLE
        def_bool $(success,$(srctree)/scripts/rust_is_available.sh)
        help

diff --git a/scripts/rustc-version.sh b/scripts/rustc-version.sh
new file mode 100755 (executable)
index 0000000..4e22593
--- /dev/null
+++ b/scripts/rustc-version.sh
@@ -0,0 +1,26 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Usage: $ ./rustc-version.sh rustc
+#
+# Print the Rust compiler version in a 6 or 7-digit form.
+
+# 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
+# `rustc` since it will reach 1.100.0 in late 2026.
+get_canonical_version()
+{
+       IFS=.
+       set -- $1
+       echo $((100000 * $1 + 100 * $2 + $3))
+}
+
+if output=$("$@" --version 2>/dev/null); then
+       set -- $output
+       get_canonical_version $2
+else
+       echo 0
+       exit 1
+fi