[RFC PATCH 1/1] scripts: Build per module Rust crates

[Martin Rodriguez Reboredo <yakoyoku@gmail.com>]

Enables compiling Rust crates as dependencies of kernel modules.

When a composite object depends on an `.rlib` file, which by the way is
a current ar archive, Kbuild will compile it from its base Rust source
and link it.

This makes possible to have Rust bindings for a subsystem that is
compiled as a module.

Signed-off-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
---
 Makefile               |  4 ++--
 scripts/Makefile.build | 10 +++++++++-
 scripts/Makefile.lib   | 19 +++++++++++++------
 3 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/Makefile b/Makefile
index 7d6be12e4c3e..7774c97e8aa0 100644
--- a/Makefile
+++ b/Makefile
@@ -283,7 +283,7 @@ no-compiler-targets := $(no-dot-config-targets) install dtbs_install \
 			headers_install modules_install modules_sign kernelrelease image_name
 no-sync-config-targets := $(no-dot-config-targets) %install modules_sign kernelrelease \
 			  image_name
-single-targets := %.a %.i %.ko %.lds %.ll %.lst %.mod %.o %.rsi %.s %.symtypes %/
+single-targets := %.a %.i %.ko %.lds %.ll %.lst %.mod %.o %.rlib %.rsi %.s %.symtypes %/
 
 config-build	:=
 mixed-build	:=
@@ -1919,7 +1919,7 @@ $(clean-dirs):
 clean: $(clean-dirs)
 	$(call cmd,rmfiles)
 	@find $(or $(KBUILD_EXTMOD), .) $(RCS_FIND_IGNORE) \
-		\( -name '*.[aios]' -o -name '*.rsi' -o -name '*.ko' -o -name '.*.cmd' \
+		\( -name '*.[aios]' -o -name '*.rlib' -o -name '*.rsi' -o -name '*.ko' -o -name '.*.cmd' \
 		-o -name '*.ko.*' \
 		-o -name '*.dtb' -o -name '*.dtbo' \
 		-o -name '*.dtb.S' -o -name '*.dtbo.S' \
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index da37bfa97211..627010518b27 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -246,7 +246,9 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
 # To make this rule robust against "Argument list too long" error,
 # ensure to add $(obj)/ prefix by a shell command.
 cmd_mod = printf '%s\n' $(call real-search, $*.o, .o, -objs -y -m) | \
-	$(AWK) '!x[$$0]++ { print("$(obj)/"$$0) }' > $@
+	$(AWK) '!x[$$0]++ { print("$(obj)/"$$0) }' > $@ && \
+	printf '%s\n' $(call real-search, $*.rlib, .rlib, -objs -y -m) | \
+	$(AWK) '!x[$$0]++ { print("--library=$(obj)/"$$0) }' >> $@
 
 $(obj)/%.mod: FORCE
 	$(call if_changed,mod)
@@ -291,6 +293,12 @@ quiet_cmd_rustc_o_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
 $(obj)/%.o: $(src)/%.rs FORCE
 	$(call if_changed_dep,rustc_o_rs)
 
+quiet_cmd_rustc_rlib_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
+      cmd_rustc_rlib_rs = $(rust_common_cmd) -Ccodegen-units=1 --emit=link=$@ $<
+
+$(obj)/%.rlib: $(src)/%.rs FORCE
+	$(call if_changed_dep,rustc_rlib_rs)
+
 quiet_cmd_rustc_rsi_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
       cmd_rustc_rsi_rs = \
 	$(rust_common_cmd) -Zunpretty=expanded $< >$@; \
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 68d0134bdbf9..6e8cfbad015d 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -53,14 +53,18 @@ multi-search = $(sort $(foreach m, $1, $(if $(call suffix-search, $m, $2, $3 -),
 real-search = $(foreach m, $1, $(if $(call suffix-search, $m, $2, $3 -), $(call suffix-search, $m, $2, $3), $m))
 
 # If $(foo-objs), $(foo-y), $(foo-m), or $(foo-) exists, foo.o is a composite object
-multi-obj-y := $(call multi-search, $(obj-y), .o, -objs -y)
-multi-obj-m := $(call multi-search, $(obj-m), .o, -objs -y -m)
+multi-obj-y := $(call multi-search, $(obj-y), .o, -objs -y) \
+	$(call multi-search, $(obj-y), .rlib, -objs -y)
+multi-obj-m := $(call multi-search, $(obj-m), .o, -objs -y -m) \
+	$(call multi-search, $(obj-m), .rlib, -objs -y -m)
 multi-obj-ym := $(multi-obj-y) $(multi-obj-m)
 
 # Replace multi-part objects by their individual parts,
 # including built-in.a from subdirectories
-real-obj-y := $(call real-search, $(obj-y), .o, -objs -y)
-real-obj-m := $(call real-search, $(obj-m), .o, -objs -y -m)
+real-obj-y := $(call real-search, $(obj-y), .o, -objs -y) \
+	$(call real-search, $(obj-y), .rlib, -objs -y)
+real-obj-m := $(call real-search, $(obj-m), .o, -objs -y -m) \
+	$(call real-search, $(obj-m), .rlib, -objs -y -m)
 
 always-y += $(always-m)
 
@@ -107,7 +111,8 @@ endif
 # Finds the multi-part object the current object will be linked into.
 # If the object belongs to two or more multi-part objects, list them all.
 modname-multi = $(sort $(foreach m,$(multi-obj-ym),\
-		$(if $(filter $*.o, $(call suffix-search, $m, .o, -objs -y -m)),$(m:.o=))))
+		$(if $(filter $*.o, $(call suffix-search, $m, .o, -objs -y -m)),$(m:.o=)) \
+		$(if $(filter $*.rlib, $(call suffix-search, $m, .rlib, -objs -y -m)),$(m:.rlib=))))
 
 __modname = $(or $(modname-multi),$(basetarget))
 
@@ -210,7 +215,9 @@ _cpp_flags += -I $(srctree)/$(src) -I $(objtree)/$(obj)
 endif
 endif
 
-part-of-module = $(if $(filter $(basename $@).o, $(real-obj-m)),y)
+part-of-module =                                             \
+	$(if $(or $(filter $(basename $@).o, $(real-obj-m)), \
+		$(filter $(basename $@).rlib, $(real-obj-m))),y)
 quiet_modtag = $(if $(part-of-module),[M],   )
 
 modkern_cflags =                                          \
-- 
2.42.0