[SRU][M][PATCH 1/1] UBUNTU: [Packaging] define Rust flags only with Rust-enabled kernels

[Andrea Righi]

To enable Rust support in the kernel we need to pass special build
flags, that are used to select the proper Rust toolchain version and
dependent components.

These flags are passed also to the scripts called during the
updateconfigs step and the build, such as 'kernelconfig', using the
$(kmake) variable.

However, $(kmake) can also contain cross-compiler variables that may
potentially affect the config or the build in certain architectures.

For this reason, avoid using kmake during 'updateconfigs' and explicitly
pass the Rust flags using a separate environment variable that will be
defined only for Rust-enabled kernels (do_lib_rust=true).

Signed-off-by: Andrea Righi <andrea.righi at canonical.com>
---
 debian/rules.d/0-common-vars.mk  |  2 --
 debian/rules.d/1-maintainer.mk   |  2 +-
 debian/rules.d/2-binary-arch.mk  | 16 ++++++++++++++++
 debian/scripts/misc/kernelconfig |  2 +-
 4 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/debian/rules.d/0-common-vars.mk b/debian/rules.d/0-common-vars.mk
index 410de315afba..d62a9b063241 100644
--- a/debian/rules.d/0-common-vars.mk
+++ b/debian/rules.d/0-common-vars.mk
@@ -238,8 +238,6 @@ kmake = make ARCH=$(build_arch) \
 	CROSS_COMPILE=$(CROSS_COMPILE) \
 	HOSTCC=$(HOSTCC) \
 	CC=$(CROSS_COMPILE)$(gcc) \
-	RUSTC=rustc-1.68 HOSTRUSTC=rustc-1.68 BINDGEN=bindgen-0.56 RUSTFMT=/usr/lib/rust-1.68/bin/rustfmt RUST_LIB_SRC=/usr/src/rustc-1.68.2/library \
-	CLANG_PATH=clang-15 LIBCLANG_PATH=/usr/lib/llvm-15/lib \
 	KERNELVERSION=$(abi_release)-$(target_flavour) \
 	CONFIG_DEBUG_SECTION_MISMATCH=y \
 	KBUILD_BUILD_VERSION="$(uploadnum)" \
diff --git a/debian/rules.d/1-maintainer.mk b/debian/rules.d/1-maintainer.mk
index 839e93a15371..a72e5fe93784 100644
--- a/debian/rules.d/1-maintainer.mk
+++ b/debian/rules.d/1-maintainer.mk
@@ -29,7 +29,7 @@ configs-targets := updateconfigs defaultconfigs genconfigs editconfigs
 .PHONY: $(configs-targets)
 $(configs-targets):
 	dh_testdir
-	kmake='$(kmake)' skip_checks=$(do_skip_checks) conc_level=$(conc_level) \
+	RUST_FLAGS='$(RUST_FLAGS)' skip_checks=$(do_skip_checks) conc_level=$(conc_level) \
 		$(SHELL) $(DROOT)/scripts/misc/kernelconfig $@
 
 .PHONY: printenv
diff --git a/debian/rules.d/2-binary-arch.mk b/debian/rules.d/2-binary-arch.mk
index 53fbb55c198a..6e9c78aadb45 100644
--- a/debian/rules.d/2-binary-arch.mk
+++ b/debian/rules.d/2-binary-arch.mk
@@ -10,6 +10,22 @@ build_cd =
 build_O  = O=$(builddir)/build-$*
 endif
 
+# Define Rust build flags only for Rust-enabled kernels
+ifeq ($(do_lib_rust),true)
+RUST_FLAGS = \
+	RUSTC=rustc-1.68 \
+	HOSTRUSTC=rustc-1.68 \
+	BINDGEN=bindgen-0.56 \
+	RUSTFMT=/usr/lib/rust-1.68/bin/rustfmt \
+	RUST_LIB_SRC=/usr/src/rustc-1.68.2/library \
+	CLANG_PATH=clang-15 \
+	LIBCLANG_PATH=/usr/lib/llvm-15/lib
+else
+RUST_FLAGS=
+endif
+
+kmake += $(RUST_FLAGS)
+
 # TODO this is probably wrong, and should be using $(DEB_HOST_MULTIARCH)
 shlibdeps_opts = $(if $(CROSS_COMPILE),-- -l$(CROSS_COMPILE:%-=/usr/%)/lib)
 
diff --git a/debian/scripts/misc/kernelconfig b/debian/scripts/misc/kernelconfig
index 035426762f8a..741650340b65 100755
--- a/debian/scripts/misc/kernelconfig
+++ b/debian/scripts/misc/kernelconfig
@@ -118,7 +118,7 @@ EOF
 	# Call config target
 	echo
 	echo "* Run ${target} on ${arch}/${flavour} ..."
-	${kmake} O=build "${env[@]}" "${target}"
+	make ${RUST_FLAGS} O=build "${env[@]}" "${target}"
 
 	# Move config for further processing
 	mv build/.config "${tmp_conf_file}"
-- 
2.40.1