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kbuild: support host programs written in Rust
This allows us to use Rust for any scripts used during compilation as long as Rust is already available, instead of e.g. C, shell scripts or Perl (Python does not seem to be required for compilation, which would be another natural & modern option to consider). After all, Rust is a good language for scripts too and the goal is to have first-class support for Rust in the kernel, so one should be able to write host programs in it too, just like with C. Not to mention the other benefits (e.g. static typing) compared to the currently available options. Eventually, if having a Rust toolchain ever becomes mandatory (whether or not Rust support is optional and/or enabled), this becomes even a better idea. Ideally, other kernel developers will also want to start using Rust for kernel tooling, which may help making that happen. A downside of Rust for this use case is `rustc`'s compilation speed, which may become concerning if e.g. a lot of programs are used. Another downside, shared with C, is the small standard library. I considered adding C object linking support, but it requires creating an archive of the C objects just for linking and a bunch of other bits which become hard to justify when we do not have a current use case for it. Like above, if having a Rust toolchain ever becomes mandatory for kernel compilation, then finding a use case where C code is needed becomes much easier. Or even the other way around, we could take advantage of Rust inside existing C programs, too. Signed-off-by: Miguel Ojeda <[email protected]>
1 parent a95777a commit 046d82f

26 files changed

+141
-21
lines changed

‎.github/workflows/ci.yaml

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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@@ -1492,6 +1492,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
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CONFIG_SAMPLE_RUST_SEMAPHORE=m
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CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
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CONFIG_SAMPLE_RUST_RANDOM=m
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CONFIG_SAMPLE_RUST_HOSTPROGS=y
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CONFIG_ARCH_HAS_DEVMEM_IS_ALLOWED=y
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# CONFIG_STRICT_DEVMEM is not set
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‎.github/workflows/kernel-ppc64le-release.config

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@@ -1454,6 +1454,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
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CONFIG_SAMPLE_RUST_SEMAPHORE=m
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CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
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CONFIG_SAMPLE_RUST_RANDOM=m
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CONFIG_SAMPLE_RUST_HOSTPROGS=y
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CONFIG_ARCH_HAS_DEVMEM_IS_ALLOWED=y
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# CONFIG_STRICT_DEVMEM is not set
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‎.github/workflows/kernel-riscv64-debug.config

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

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

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

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

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@@ -1441,6 +1441,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
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CONFIG_SAMPLE_RUST_SEMAPHORE=m
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CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
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CONFIG_SAMPLE_RUST_RANDOM=m
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CONFIG_SAMPLE_RUST_HOSTPROGS=y
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CONFIG_ARCH_HAS_DEVMEM_IS_ALLOWED=y
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# CONFIG_STRICT_DEVMEM is not set
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‎.github/workflows/kernel-x86_64-debug.config

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@@ -1444,6 +1444,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
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CONFIG_SAMPLE_RUST_SEMAPHORE=m
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CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
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CONFIG_SAMPLE_RUST_RANDOM=m
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CONFIG_SAMPLE_RUST_HOSTPROGS=y
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CONFIG_ARCH_HAS_DEVMEM_IS_ALLOWED=y
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# CONFIG_STRICT_DEVMEM is not set
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‎.github/workflows/kernel-x86_64-release-thinlto.config

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@@ -1397,6 +1397,7 @@ CONFIG_SAMPLE_RUST_STACK_PROBING=m
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CONFIG_SAMPLE_RUST_SEMAPHORE=m
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CONFIG_SAMPLE_RUST_SEMAPHORE_C=m
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CONFIG_SAMPLE_RUST_RANDOM=m
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CONFIG_SAMPLE_RUST_HOSTPROGS=y
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CONFIG_ARCH_HAS_DEVMEM_IS_ALLOWED=y
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# CONFIG_STRICT_DEVMEM is not set
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‎.github/workflows/kernel-x86_64-release.config

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

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

‎Documentation/kbuild/makefiles.rst

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@@ -29,8 +29,9 @@ This document describes the Linux kernel Makefiles.
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--- 4.1 Simple Host Program
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--- 4.2 Composite Host Programs
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--- 4.3 Using C++ for host programs
32-
--- 4.4 Controlling compiler options for host programs
33-
--- 4.5 When host programs are actually built
32+
--- 4.4 Using Rust for host programs
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--- 4.5 Controlling compiler options for host programs
34+
--- 4.6 When host programs are actually built
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=== 5 Userspace Program support
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--- 5.1 Simple Userspace Program
@@ -835,7 +836,24 @@ Both possibilities are described in the following.
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qconf-cxxobjs := qconf.o
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qconf-objs := check.o
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838-
4.4 Controlling compiler options for host programs
839+
4.4 Using Rust for host programs
840+
--------------------------------
841+
842+
Kbuild offers support for host programs written in Rust. However,
843+
since a Rust toolchain is not mandatory for kernel compilation,
844+
it may only be used in scenarios where Rust is required to be
845+
available (e.g. when ``CONFIG_RUST`` is enabled).
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847+
Example::
848+
849+
hostprogs := target
850+
target-rust := y
851+
852+
Kbuild will compile ``target`` using ``target.rs`` as the crate root,
853+
located in the same directory as the ``Makefile``. The crate may
854+
consist of several source files (see ``samples/rust/hostprogs``).
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856+
4.5 Controlling compiler options for host programs
839857
--------------------------------------------------
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841859
When compiling host programs, it is possible to set specific flags.
@@ -867,7 +885,7 @@ Both possibilities are described in the following.
867885
When linking qconf, it will be passed the extra option
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"-L$(QTDIR)/lib".
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870-
4.5 When host programs are actually built
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4.6 When host programs are actually built
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-----------------------------------------
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Kbuild will only build host-programs when they are referenced

‎Makefile

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@@ -437,13 +437,32 @@ else
437437
HOSTCC = gcc
438438
HOSTCXX = g++
439439
endif
440+
HOSTRUSTC = rustc
440441

441442
export KBUILD_USERCFLAGS := -Wall -Wmissing-prototypes -Wstrict-prototypes \
442443
-O2 -fomit-frame-pointer -std=gnu89
443444
export KBUILD_USERLDFLAGS :=
444445

446+
# These flags apply to all Rust code in the tree, including the kernel and
447+
# host programs.
448+
rust_common_flags := --edition=2021 \
449+
-Zbinary_dep_depinfo=y \
450+
-Dunsafe_op_in_unsafe_fn -Drust_2018_idioms \
451+
-Dunreachable_pub -Dnon_ascii_idents \
452+
-Wmissing_docs \
453+
-Drustdoc::missing_crate_level_docs \
454+
-Dclippy::correctness -Dclippy::style \
455+
-Dclippy::suspicious -Dclippy::complexity \
456+
-Dclippy::perf \
457+
-Dclippy::let_unit_value -Dclippy::mut_mut \
458+
-Dclippy::needless_bitwise_bool \
459+
-Dclippy::needless_continue \
460+
-Wclippy::dbg_macro
461+
445462
KBUILD_HOSTCFLAGS := $(KBUILD_USERCFLAGS) $(HOST_LFS_CFLAGS) $(HOSTCFLAGS)
446463
KBUILD_HOSTCXXFLAGS := -Wall -O2 $(HOST_LFS_CFLAGS) $(HOSTCXXFLAGS)
464+
KBUILD_HOSTRUSTFLAGS := $(rust_common_flags) -O -Zallow-features= \
465+
$(HOSTRUSTFLAGS)
447466
KBUILD_HOSTLDFLAGS := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS)
448467
KBUILD_HOSTLDLIBS := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
449468

@@ -533,20 +552,12 @@ KBUILD_CFLAGS := -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs \
533552
-std=gnu89
534553
KBUILD_CPPFLAGS := -D__KERNEL__
535554
KBUILD_RUST_TARGET := $(srctree)/arch/$(SRCARCH)/rust/target.json
536-
KBUILD_RUSTFLAGS := --edition=2021 \
537-
-Cpanic=abort -Cembed-bitcode=n -Clto=n -Crpath=n \
538-
-Cforce-unwind-tables=n -Ccodegen-units=1 \
539-
-Csymbol-mangling-version=v0 \
540-
-Zbinary_dep_depinfo=y \
541-
-Dunsafe_op_in_unsafe_fn -Drust_2018_idioms \
542-
-Dunreachable_pub -Dnon_ascii_idents \
543-
-Wmissing_docs \
544-
-Drustdoc::missing_crate_level_docs \
545-
-Dclippy::correctness -Dclippy::style -Dclippy::suspicious \
546-
-Dclippy::complexity -Dclippy::perf -Dclippy::float_arithmetic \
547-
-Dclippy::let_unit_value -Dclippy::mut_mut \
548-
-Dclippy::needless_bitwise_bool -Dclippy::needless_continue \
549-
-Wclippy::dbg_macro
555+
KBUILD_RUSTFLAGS := $(rust_common_flags) \
556+
-Cpanic=abort -Cembed-bitcode=n -Clto=n -Crpath=n \
557+
-Cforce-unwind-tables=n -Ccodegen-units=1 \
558+
-Csymbol-mangling-version=v0 \
559+
-Dclippy::float_arithmetic
560+
550561
KBUILD_AFLAGS_KERNEL :=
551562
KBUILD_CFLAGS_KERNEL :=
552563
KBUILD_RUSTFLAGS_KERNEL :=
@@ -573,6 +584,7 @@ export RUSTC_BOOTSTRAP := 1
573584

574585
export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE LD CC
575586
export RUSTC RUSTDOC RUSTFMT RUSTC_OR_CLIPPY_QUIET RUSTC_OR_CLIPPY BINDGEN CARGO
587+
export HOSTRUSTC KBUILD_HOSTRUSTFLAGS
576588
export CPP AR NM STRIP OBJCOPY OBJDUMP READELF PAHOLE RESOLVE_BTFIDS LEX YACC AWK INSTALLKERNEL
577589
export PERL PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
578590
export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ ZSTD

‎samples/rust/Kconfig

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@@ -120,4 +120,11 @@ config SAMPLE_RUST_PLATFORM
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121121
If unsure, say N.
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123+
config SAMPLE_RUST_HOSTPROGS
124+
bool "Host programs"
125+
help
126+
This option builds the Rust host program samples.
127+
128+
If unsure, say N.
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123130
endif # SAMPLES_RUST

‎samples/rust/Makefile

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@@ -11,3 +11,5 @@ obj-$(CONFIG_SAMPLE_RUST_SEMAPHORE) += rust_semaphore.o
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obj-$(CONFIG_SAMPLE_RUST_SEMAPHORE_C) += rust_semaphore_c.o
1212
obj-$(CONFIG_SAMPLE_RUST_RANDOM) += rust_random.o
1313
obj-$(CONFIG_SAMPLE_RUST_PLATFORM) += rust_platform.o
14+
15+
subdir-$(CONFIG_SAMPLE_RUST_HOSTPROGS) += hostprogs

‎samples/rust/hostprogs/.gitignore

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# SPDX-License-Identifier: GPL-2.0
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single

‎samples/rust/hostprogs/Makefile

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# SPDX-License-Identifier: GPL-2.0
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hostprogs-always-y := single
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single-rust := y

‎samples/rust/hostprogs/a.rs

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// SPDX-License-Identifier: GPL-2.0
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//! Rust single host program sample: module `a`.
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5+
pub(crate) fn f(x: i32) {
6+
println!("The number is {}.", x);
7+
}

‎samples/rust/hostprogs/b.rs

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

‎samples/rust/hostprogs/single.rs

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

‎scripts/Makefile.host

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@@ -22,6 +22,8 @@ $(obj)/%.tab.c $(obj)/%.tab.h: $(src)/%.y FORCE
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# to preprocess a data file.
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#
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# Both C and C++ are supported, but preferred language is C for such utilities.
25+
# Rust is also supported, but it may only be used in scenarios where a Rust
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# toolchain is required to be available (e.g. when `CONFIG_RUST` is enabled).
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#
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# Sample syntax (see Documentation/kbuild/makefiles.rst for reference)
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# hostprogs := bin2hex
@@ -37,15 +39,20 @@ $(obj)/%.tab.c $(obj)/%.tab.h: $(src)/%.y FORCE
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# qconf-objs := menu.o
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# Will compile qconf as a C++ program, and menu as a C program.
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# They are linked as C++ code to the executable qconf
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#
43+
# hostprogs := target
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# target-rust := y
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# Will compile `target` as a Rust program, using `target.rs` as the crate root.
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# The crate may consist of several source files.
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# C code
4249
# Executables compiled from a single .c file
4350
host-csingle := $(foreach m,$(hostprogs), \
44-
$(if $($(m)-objs)$($(m)-cxxobjs),,$(m)))
51+
$(if $($(m)-objs)$($(m)-cxxobjs)$($(m)-rust),,$(m)))
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# C executables linked based on several .o files
4754
host-cmulti := $(foreach m,$(hostprogs),\
48-
$(if $($(m)-cxxobjs),,$(if $($(m)-objs),$(m))))
55+
$(if $($(m)-cxxobjs)$($(m)-rust),,$(if $($(m)-objs),$(m))))
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# Object (.o) files compiled from .c files
5158
host-cobjs := $(sort $(foreach m,$(hostprogs),$($(m)-objs)))
@@ -58,11 +65,17 @@ host-cxxmulti := $(foreach m,$(hostprogs),$(if $($(m)-cxxobjs),$(m)))
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# C++ Object (.o) files compiled from .cc files
5966
host-cxxobjs := $(sort $(foreach m,$(host-cxxmulti),$($(m)-cxxobjs)))
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# Rust code
69+
# Executables compiled from a single Rust crate (which may consist of
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# one or more .rs files)
71+
host-rust := $(foreach m,$(hostprogs),$(if $($(m)-rust),$(m)))
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host-csingle := $(addprefix $(obj)/,$(host-csingle))
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host-cmulti := $(addprefix $(obj)/,$(host-cmulti))
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host-cobjs := $(addprefix $(obj)/,$(host-cobjs))
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host-cxxmulti := $(addprefix $(obj)/,$(host-cxxmulti))
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host-cxxobjs := $(addprefix $(obj)/,$(host-cxxobjs))
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host-rust := $(addprefix $(obj)/,$(host-rust))
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#####
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# Handle options to gcc. Support building with separate output directory
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$(HOSTCFLAGS_$(target-stem).o)
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_hostcxx_flags = $(KBUILD_HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
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$(HOSTCXXFLAGS_$(target-stem).o)
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_hostrust_flags = $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
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$(HOSTRUSTFLAGS_$(target-stem))
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# $(objtree)/$(obj) for including generated headers from checkin source files
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ifeq ($(KBUILD_EXTMOD),)
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8398
hostc_flags = -Wp,-MMD,$(depfile) $(_hostc_flags)
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hostcxx_flags = -Wp,-MMD,$(depfile) $(_hostcxx_flags)
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hostrust_flags = $(_hostrust_flags)
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#####
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# Compile programs on the host
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128144
$(host-cxxobjs): $(obj)/%.o: $(src)/%.cc FORCE
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$(call if_changed_dep,host-cxxobjs)
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# Create executable from a single Rust crate (which may consist of
148+
# one or more `.rs` files)
149+
# host-rust -> Executable
150+
quiet_cmd_host-rust = HOSTRUSTC $@
151+
cmd_host-rust = \
152+
$(HOSTRUSTC) $(hostrust_flags) --emit=dep-info,link \
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--out-dir=$(obj)/ $<; \
154+
mv $(obj)/$(target-stem).d $(depfile); \
155+
sed -i '/^\#/d' $(depfile)
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$(host-rust): $(obj)/%: $(src)/%.rs FORCE
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$(call if_changed_dep,host-rust)
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targets += $(host-csingle) $(host-cmulti) $(host-cobjs) \
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$(host-cxxmulti) $(host-cxxobjs)
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$(host-cxxmulti) $(host-cxxobjs) $(host-rust)

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