Merge pull request torvalds#692 from ojeda/hostprogs

kbuild: support host programs written in Rust

.github/workflows/ci.yaml

@@ -405,5 +405,8 @@ jobs:
           grep -F '.text'                       ${{ env.BUILD_DIR }}samples/rust/rust_minimal.s
           grep -F '; ModuleID'                  ${{ env.BUILD_DIR }}samples/rust/rust_minimal.ll
 
+      # Rust host programs
+      - run: ${{ env.BUILD_DIR }}samples/rust/hostprogs/single | grep -F 'The number is 42.'
+
       # View changes to ccache
       - run: ccache -s

.github/workflows/kernel-arm-debug.config

@@ -1780,6 +1780,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
 CONFIG_SAMPLE_RUST_SEMAPHORE=m
 CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
 CONFIG_SAMPLE_RUST_RANDOM=m
+CONFIG_SAMPLE_RUST_HOSTPROGS=y
 # CONFIG_STRICT_DEVMEM is not set
 
 #

.github/workflows/kernel-arm-release.config

@@ -1704,6 +1704,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
 CONFIG_SAMPLE_RUST_SEMAPHORE=m
 CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
 CONFIG_SAMPLE_RUST_RANDOM=m
+CONFIG_SAMPLE_RUST_HOSTPROGS=y
 # CONFIG_STRICT_DEVMEM is not set
 
 #

.github/workflows/kernel-arm64-debug-thinlto.config

@@ -1437,6 +1437,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
 CONFIG_SAMPLE_RUST_SEMAPHORE=m
 CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
 CONFIG_SAMPLE_RUST_RANDOM=m
+CONFIG_SAMPLE_RUST_HOSTPROGS=y
 
 #
 # arm64 Debugging

.github/workflows/kernel-arm64-debug.config

@@ -1432,6 +1432,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
 CONFIG_SAMPLE_RUST_SEMAPHORE=m
 CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
 CONFIG_SAMPLE_RUST_RANDOM=m
+CONFIG_SAMPLE_RUST_HOSTPROGS=y
 
 #
 # arm64 Debugging

.github/workflows/kernel-arm64-release-thinlto.config

@@ -1355,6 +1355,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
 CONFIG_SAMPLE_RUST_SEMAPHORE=m
 CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
 CONFIG_SAMPLE_RUST_RANDOM=m
+CONFIG_SAMPLE_RUST_HOSTPROGS=y
 
 #
 # arm64 Debugging

.github/workflows/kernel-arm64-release.config

@@ -1350,6 +1350,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
 CONFIG_SAMPLE_RUST_SEMAPHORE=m
 CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
 CONFIG_SAMPLE_RUST_RANDOM=m
+CONFIG_SAMPLE_RUST_HOSTPROGS=y
 
 #
 # arm64 Debugging

.github/workflows/kernel-ppc64le-debug.config

@@ -1492,6 +1492,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
 CONFIG_SAMPLE_RUST_SEMAPHORE=m
 CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
 CONFIG_SAMPLE_RUST_RANDOM=m
+CONFIG_SAMPLE_RUST_HOSTPROGS=y
 CONFIG_ARCH_HAS_DEVMEM_IS_ALLOWED=y
 # CONFIG_STRICT_DEVMEM is not set
 

.github/workflows/kernel-ppc64le-release.config

@@ -1454,6 +1454,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
 CONFIG_SAMPLE_RUST_SEMAPHORE=m
 CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
 CONFIG_SAMPLE_RUST_RANDOM=m
+CONFIG_SAMPLE_RUST_HOSTPROGS=y
 CONFIG_ARCH_HAS_DEVMEM_IS_ALLOWED=y
 # CONFIG_STRICT_DEVMEM is not set
 

.github/workflows/kernel-riscv64-debug.config

@@ -1286,6 +1286,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
 CONFIG_SAMPLE_RUST_SEMAPHORE=m
 CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
 CONFIG_SAMPLE_RUST_RANDOM=m
+CONFIG_SAMPLE_RUST_HOSTPROGS=y
 # CONFIG_STRICT_DEVMEM is not set
 
 #

.github/workflows/kernel-riscv64-release.config

@@ -1202,6 +1202,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
 CONFIG_SAMPLE_RUST_SEMAPHORE=m
 CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
 CONFIG_SAMPLE_RUST_RANDOM=m
+CONFIG_SAMPLE_RUST_HOSTPROGS=y
 # CONFIG_STRICT_DEVMEM is not set
 
 #

.github/workflows/kernel-x86_64-debug-thinlto.config

@@ -1441,6 +1441,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
 CONFIG_SAMPLE_RUST_SEMAPHORE=m
 CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
 CONFIG_SAMPLE_RUST_RANDOM=m
+CONFIG_SAMPLE_RUST_HOSTPROGS=y
 CONFIG_ARCH_HAS_DEVMEM_IS_ALLOWED=y
 # CONFIG_STRICT_DEVMEM is not set
 

.github/workflows/kernel-x86_64-debug.config

@@ -1444,6 +1444,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
 CONFIG_SAMPLE_RUST_SEMAPHORE=m
 CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
 CONFIG_SAMPLE_RUST_RANDOM=m
+CONFIG_SAMPLE_RUST_HOSTPROGS=y
 CONFIG_ARCH_HAS_DEVMEM_IS_ALLOWED=y
 # CONFIG_STRICT_DEVMEM is not set
 

.github/workflows/kernel-x86_64-release-thinlto.config

@@ -1397,6 +1397,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
 CONFIG_SAMPLE_RUST_SEMAPHORE=m
 CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
 CONFIG_SAMPLE_RUST_RANDOM=m
+CONFIG_SAMPLE_RUST_HOSTPROGS=y
 CONFIG_ARCH_HAS_DEVMEM_IS_ALLOWED=y
 # CONFIG_STRICT_DEVMEM is not set
 

.github/workflows/kernel-x86_64-release.config

@@ -1392,6 +1392,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
 CONFIG_SAMPLE_RUST_SEMAPHORE=m
 CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
 CONFIG_SAMPLE_RUST_RANDOM=m
+CONFIG_SAMPLE_RUST_HOSTPROGS=y
 CONFIG_ARCH_HAS_DEVMEM_IS_ALLOWED=y
 # CONFIG_STRICT_DEVMEM is not set
 

Documentation/kbuild/kbuild.rst

@@ -82,6 +82,10 @@ HOSTCXXFLAGS
 ------------
 Additional flags to be passed to $(HOSTCXX) when building host programs.
 
+HOSTRUSTFLAGS
+-------------
+Additional flags to be passed to $(HOSTRUSTC) when building host programs.
+
 HOSTLDFLAGS
 -----------
 Additional flags to be passed when linking host programs.

Documentation/kbuild/makefiles.rst

@@ -29,8 +29,9 @@ This document describes the Linux kernel Makefiles.
 	   --- 4.1 Simple Host Program
 	   --- 4.2 Composite Host Programs
 	   --- 4.3 Using C++ for host programs
-	   --- 4.4 Controlling compiler options for host programs
-	   --- 4.5 When host programs are actually built
+	   --- 4.4 Using Rust for host programs
+	   --- 4.5 Controlling compiler options for host programs
+	   --- 4.6 When host programs are actually built
 
 	=== 5 Userspace Program support
 	   --- 5.1 Simple Userspace Program
@@ -835,7 +836,24 @@ Both possibilities are described in the following.
 		qconf-cxxobjs := qconf.o
 		qconf-objs    := check.o
 
-4.4 Controlling compiler options for host programs
+4.4 Using Rust for host programs
+--------------------------------
+
+	Kbuild offers support for host programs written in Rust. However,
+	since a Rust toolchain is not mandatory for kernel compilation,
+	it may only be used in scenarios where Rust is required to be
+	available (e.g. when  ``CONFIG_RUST`` is enabled).
+
+	Example::
+
+		hostprogs     := target
+		target-rust   := y
+
+	Kbuild will compile ``target`` using ``target.rs`` as the crate root,
+	located in the same directory as the ``Makefile``. The crate may
+	consist of several source files (see ``samples/rust/hostprogs``).
+
+4.5 Controlling compiler options for host programs
 --------------------------------------------------
 
 	When compiling host programs, it is possible to set specific flags.
@@ -867,7 +885,7 @@ Both possibilities are described in the following.
 	When linking qconf, it will be passed the extra option
 	"-L$(QTDIR)/lib".
 
-4.5 When host programs are actually built
+4.6 When host programs are actually built
 -----------------------------------------
 
 	Kbuild will only build host-programs when they are referenced

Makefile

@@ -437,13 +437,32 @@ else
 HOSTCC	= gcc
 HOSTCXX	= g++
 endif
+HOSTRUSTC = rustc
 
 export KBUILD_USERCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \
 			      -O2 -fomit-frame-pointer -std=gnu89
 export KBUILD_USERLDFLAGS :=
 
+# These flags apply to all Rust code in the tree, including the kernel and
+# host programs.
+rust_common_flags := --edition=2021 \
+		     -Zbinary_dep_depinfo=y \
+		     -Dunsafe_op_in_unsafe_fn -Drust_2018_idioms \
+		     -Dunreachable_pub -Dnon_ascii_idents \
+		     -Wmissing_docs \
+		     -Drustdoc::missing_crate_level_docs \
+		     -Dclippy::correctness -Dclippy::style \
+		     -Dclippy::suspicious -Dclippy::complexity \
+		     -Dclippy::perf \
+		     -Dclippy::let_unit_value -Dclippy::mut_mut \
+		     -Dclippy::needless_bitwise_bool \
+		     -Dclippy::needless_continue \
+		     -Wclippy::dbg_macro
+
 KBUILD_HOSTCFLAGS   := $(KBUILD_USERCFLAGS) $(HOST_LFS_CFLAGS) $(HOSTCFLAGS)
 KBUILD_HOSTCXXFLAGS := -Wall -O2 $(HOST_LFS_CFLAGS) $(HOSTCXXFLAGS)
+KBUILD_HOSTRUSTFLAGS := $(rust_common_flags) -O -Zallow-features= \
+			$(HOSTRUSTFLAGS)
 KBUILD_HOSTLDFLAGS  := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS)
 KBUILD_HOSTLDLIBS   := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
 
@@ -533,20 +552,12 @@ KBUILD_CFLAGS   := -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs \
 		   -std=gnu89
 KBUILD_CPPFLAGS := -D__KERNEL__
 KBUILD_RUST_TARGET := $(srctree)/arch/$(SRCARCH)/rust/target.json
-KBUILD_RUSTFLAGS := --edition=2021 \
-		     -Cpanic=abort -Cembed-bitcode=n -Clto=n -Crpath=n \
-		     -Cforce-unwind-tables=n -Ccodegen-units=1 \
-		     -Csymbol-mangling-version=v0 \
-		     -Zbinary_dep_depinfo=y \
-		     -Dunsafe_op_in_unsafe_fn -Drust_2018_idioms \
-		     -Dunreachable_pub -Dnon_ascii_idents \
-		     -Wmissing_docs \
-		     -Drustdoc::missing_crate_level_docs \
-		     -Dclippy::correctness -Dclippy::style -Dclippy::suspicious \
-		     -Dclippy::complexity -Dclippy::perf -Dclippy::float_arithmetic \
-		     -Dclippy::let_unit_value -Dclippy::mut_mut \
-		     -Dclippy::needless_bitwise_bool -Dclippy::needless_continue \
-		     -Wclippy::dbg_macro
+KBUILD_RUSTFLAGS := $(rust_common_flags) \
+		    -Cpanic=abort -Cembed-bitcode=n -Clto=n -Crpath=n \
+		    -Cforce-unwind-tables=n -Ccodegen-units=1 \
+		    -Csymbol-mangling-version=v0 \
+		    -Dclippy::float_arithmetic
+
 KBUILD_AFLAGS_KERNEL :=
 KBUILD_CFLAGS_KERNEL :=
 KBUILD_RUSTFLAGS_KERNEL :=
@@ -573,6 +584,7 @@ export RUSTC_BOOTSTRAP := 1
 
 export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE LD CC
 export RUSTC RUSTDOC RUSTFMT RUSTC_OR_CLIPPY_QUIET RUSTC_OR_CLIPPY BINDGEN CARGO
+export HOSTRUSTC KBUILD_HOSTRUSTFLAGS
 export CPP AR NM STRIP OBJCOPY OBJDUMP READELF PAHOLE RESOLVE_BTFIDS LEX YACC AWK INSTALLKERNEL
 export PERL PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
 export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ ZSTD

samples/rust/Kconfig

@@ -120,4 +120,11 @@ config SAMPLE_RUST_PLATFORM
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_HOSTPROGS
+	bool "Host programs"
+	help
+	  This option builds the Rust host program samples.
+
+	  If unsure, say N.
+
 endif # SAMPLES_RUST

samples/rust/Makefile

@@ -11,3 +11,5 @@ obj-$(CONFIG_SAMPLE_RUST_SEMAPHORE)		+= rust_semaphore.o
 obj-$(CONFIG_SAMPLE_RUST_SEMAPHORE_C)		+= rust_semaphore_c.o
 obj-$(CONFIG_SAMPLE_RUST_RANDOM)		+= rust_random.o
 obj-$(CONFIG_SAMPLE_RUST_PLATFORM)		+= rust_platform.o
+
+subdir-$(CONFIG_SAMPLE_RUST_HOSTPROGS)		+= hostprogs

samples/rust/hostprogs/.gitignore

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+single

samples/rust/hostprogs/Makefile

@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+
+hostprogs-always-y := single
+
+single-rust := y

samples/rust/hostprogs/a.rs

@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust single host program sample: module `a`.
+
+pub(crate) fn f(x: i32) {
+    println!("The number is {}.", x);
+}

samples/rust/hostprogs/b.rs

@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust single host program sample: module `b`.
+
+pub(crate) const CONSTANT: i32 = 42;

samples/rust/hostprogs/single.rs

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust single host program sample.
+
+mod a;
+mod b;
+
+fn main() {
+    println!("Hello world!");
+
+    a::f(b::CONSTANT);
+}

scripts/Makefile.host

@@ -22,6 +22,8 @@ $(obj)/%.tab.c $(obj)/%.tab.h: $(src)/%.y FORCE
 # to preprocess a data file.
 #
 # Both C and C++ are supported, but preferred language is C for such utilities.
+# Rust is also supported, but it may only be used in scenarios where a Rust
+# toolchain is required to be available (e.g. when  `CONFIG_RUST` is enabled).
 #
 # Sample syntax (see Documentation/kbuild/makefiles.rst for reference)
 # hostprogs := bin2hex
@@ -37,15 +39,20 @@ $(obj)/%.tab.c $(obj)/%.tab.h: $(src)/%.y FORCE
 # qconf-objs      := menu.o
 # Will compile qconf as a C++ program, and menu as a C program.
 # They are linked as C++ code to the executable qconf
+#
+# hostprogs   := target
+# target-rust := y
+# Will compile `target` as a Rust program, using `target.rs` as the crate root.
+# The crate may consist of several source files.
 
 # C code
 # Executables compiled from a single .c file
 host-csingle	:= $(foreach m,$(hostprogs), \
-			$(if $($(m)-objs)$($(m)-cxxobjs),,$(m)))
+			$(if $($(m)-objs)$($(m)-cxxobjs)$($(m)-rust),,$(m)))
 
 # C executables linked based on several .o files
 host-cmulti	:= $(foreach m,$(hostprogs),\
-		   $(if $($(m)-cxxobjs),,$(if $($(m)-objs),$(m))))
+		   $(if $($(m)-cxxobjs)$($(m)-rust),,$(if $($(m)-objs),$(m))))
 
 # Object (.o) files compiled from .c files
 host-cobjs	:= $(sort $(foreach m,$(hostprogs),$($(m)-objs)))
@@ -58,11 +65,17 @@ host-cxxmulti	:= $(foreach m,$(hostprogs),$(if $($(m)-cxxobjs),$(m)))
 # C++ Object (.o) files compiled from .cc files
 host-cxxobjs	:= $(sort $(foreach m,$(host-cxxmulti),$($(m)-cxxobjs)))
 
+# Rust code
+# Executables compiled from a single Rust crate (which may consist of
+# one or more .rs files)
+host-rust	:= $(foreach m,$(hostprogs),$(if $($(m)-rust),$(m)))
+
 host-csingle	:= $(addprefix $(obj)/,$(host-csingle))
 host-cmulti	:= $(addprefix $(obj)/,$(host-cmulti))
 host-cobjs	:= $(addprefix $(obj)/,$(host-cobjs))
 host-cxxmulti	:= $(addprefix $(obj)/,$(host-cxxmulti))
 host-cxxobjs	:= $(addprefix $(obj)/,$(host-cxxobjs))
+host-rust	:= $(addprefix $(obj)/,$(host-rust))
 
 #####
 # Handle options to gcc. Support building with separate output directory
@@ -71,6 +84,8 @@ _hostc_flags   = $(KBUILD_HOSTCFLAGS)   $(HOST_EXTRACFLAGS)   \
                  $(HOSTCFLAGS_$(target-stem).o)
 _hostcxx_flags = $(KBUILD_HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
                  $(HOSTCXXFLAGS_$(target-stem).o)
+_hostrust_flags = $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
+                  $(HOSTRUSTFLAGS_$(target-stem))
 
 # $(objtree)/$(obj) for including generated headers from checkin source files
 ifeq ($(KBUILD_EXTMOD),)
@@ -82,6 +97,7 @@ endif
 
 hostc_flags    = -Wp,-MMD,$(depfile) $(_hostc_flags)
 hostcxx_flags  = -Wp,-MMD,$(depfile) $(_hostcxx_flags)
+hostrust_flags = $(_hostrust_flags)
 
 #####
 # Compile programs on the host
@@ -128,5 +144,17 @@ quiet_cmd_host-cxxobjs	= HOSTCXX $@
 $(host-cxxobjs): $(obj)/%.o: $(src)/%.cc FORCE
 	$(call if_changed_dep,host-cxxobjs)
 
+# Create executable from a single Rust crate (which may consist of
+# one or more `.rs` files)
+# host-rust -> Executable
+quiet_cmd_host-rust	= HOSTRUSTC $@
+      cmd_host-rust	= \
+	$(HOSTRUSTC) $(hostrust_flags) --emit=dep-info,link \
+		--out-dir=$(obj)/ $<; \
+	mv $(obj)/$(target-stem).d $(depfile); \
+	sed -i '/^\#/d' $(depfile)
+$(host-rust): $(obj)/%: $(src)/%.rs FORCE
+	$(call if_changed_dep,host-rust)
+
 targets += $(host-csingle) $(host-cmulti) $(host-cobjs) \
-	   $(host-cxxmulti) $(host-cxxobjs)
+	   $(host-cxxmulti) $(host-cxxobjs) $(host-rust)