[Buildroot] [RFC PATCH 0/5] Add Rust for Linux support

[Buildroot] [RFC PATCH 0/5] Add Rust for Linux support

[El Mehdi YOUNES via buildroot]

This series is a best-effort to share our work and ideas on enabling
Rust-for-Linux from Buildroot, and to request help and further ideas from
the community.

- bindgen → clang/libclang
  From prior bindgen use in Mesa and Rust-for-Linux guidance, bindgen needs
  libclang available at build time. We therefore add a host-clang dependency
  for host bindgen and consider it mandatory in this context.

- rust std sources for the kernel
  Rust-for-Linux needs the std sources (e.g. core/lib.rs). We download
  rustc-<ver>-src.tar.xz and install only the library/ subtree to:
    $(HOST_DIR)/lib/rustlib/src/rust/
  Extra downloads are split (std vs sources) to avoid conflicts. A possible
  improvement is to install sources only when the kernel Rust option is
  enabled; this is not done yet but is feasible.

- rustfmt (clippy optional)
  The kernel requires rustfmt; we install it (component name is
  rustfmt-preview). Clippy is optional for developers and is not included
  in this round.

- Kernel Kconfig check vs build order
  Enabling Rust in the kernel depends on host tools being present due to
  the early availability check:
    https://github.com/torvalds/linux/blob/master/scripts/rust_is_available.sh
    https://github.com/torvalds/linux/blob/master/init/Kconfig#L70
  To cope with this, we add a Buildroot menu option to wire Rust tools and
  paths. In practice, it is a two-step flow: build once (tools become
  available), then enable Rust drivers/samples via linux-menuconfig.

- HOSTCC handling (rustc -Clinker)
  A change is needed in how HOSTCC is passed to the kernel build; the
  current embedding of flags into HOSTCC does not work with rustc’s
  -Clinker. The 4th patch addresses this by splitting the compiler from
  its flags and using Kbuild’s host-side variables (available since
  v4.19). Guidance is welcome on gating for older kernels (< 4.19): tie
  it to BR2_LINUX_KERNEL_RUST_SUPPORT, require headers >= 4.19, or any
  alternative the maintainers recommend.

This series does not claim that Rust-for-Linux should be a priority right
now; upstream is still evolving and kernel-side support is young. However,
we expect that enabling Rust will eventually become necessary in Buildroot.
It is better to prepare the integration and agree on gating now, so we are
ready when the ecosystem stabilizes.

Best regards,
El Mehdi YOUNES

El Mehdi YOUNES (5):
  package/rust-bindgen: add host-clang dependency
  package/rust-bin: add Rust sources
  package/rust-bin: install rustfmt
  linux: split HOSTCC from flags
  linux: Add Rust support

 linux/Config.in                      |  6 ++++++
 linux/linux.mk                       | 16 +++++++++++++++-
 package/rust-bin/rust-bin.hash       |  2 ++
 package/rust-bin/rust-bin.mk         | 20 +++++++++++++++++---
 package/rust-bindgen/rust-bindgen.mk |  2 ++
 utils/update-rust                    |  9 +++++++++
 6 files changed, 51 insertions(+), 4 deletions(-)

-- 
2.43.0

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[Buildroot] [RFC PATCH 1/5] package/rust-bindgen: add host-clang dependency

[El Mehdi YOUNES via buildroot]

According to the official requirements, bindgen needs libclang to
parse C/C++ headers. Until now the tool was used mainly by Mesa and
worked, but Rust-for-Linux explicitly relies on bindgen + libclang,
otherwise we can't activate Rust for linux.

See
https://rust-lang.github.io/rust-bindgen/requirements.html

Signed-off-by: El Mehdi YOUNES <elmehdi.younes@smile.fr>
---
 package/rust-bindgen/rust-bindgen.mk | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/package/rust-bindgen/rust-bindgen.mk b/package/rust-bindgen/rust-bindgen.mk
index 349d4c3670..0ec620002a 100644
--- a/package/rust-bindgen/rust-bindgen.mk
+++ b/package/rust-bindgen/rust-bindgen.mk
@@ -9,6 +9,8 @@ RUST_BINDGEN_SITE = $(call github,rust-lang,rust-bindgen,v$(RUST_BINDGEN_VERSION
 RUST_BINDGEN_LICENSE = BSD-3-clause
 RUST_BINDGEN_LICENSE_FILES = LICENSE
 
+HOST_RUST_BINDGEN_DEPENDENCIES = host-clang
+
 # The Cargo.toml at the root directory is a "virtual manifest".
 # Since we only want to build and install bindgen use the Cargo.toml
 # from the bindgen-cli subdirectory.
-- 
2.43.0

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[Buildroot] [RFC PATCH 2/5] package/rust-bin: add Rust sources

[El Mehdi YOUNES via buildroot]

Rust-for-Linux requires the Rust standard library sources (e.g. core/lib.rs)
to enable CONFIG_RUST. This patch provides them in rust-bin while keeping the
prebuilt compiler tarball unchanged.

It adds HOST_RUST_BIN_SOURCE_TARBALL = rustc-$(VER)-src.tar.xz to
HOST_RUST_BIN_EXTRA_DOWNLOADS, and splits extra downloads into
HOST_RUST_BIN_STD_TARBALLS (rust-std-*) and HOST_RUST_BIN_SOURCE_TARBALL so
extraction is controlled separately: rust-std-* are unpacked under $(@D)/std,
and rustc-<ver>-src.tar.xz is unpacked to rust-src then only the 'library/'
subtree from the source tarball is installed $(HOST_DIR)/lib/rustlib/src/rust/.

The utils/update-rust script is also extended to generate the sha256 line for
rustc-<ver>-src.tar.xz in package/rust-bin/rust-bin.hash.

see
https://github.com/torvalds/linux/blob/master/Documentation/rust/quick-start.rst

Signed-off-by: El Mehdi YOUNES <elmehdi.younes@smile.fr>
---
 package/rust-bin/rust-bin.hash |  2 ++
 package/rust-bin/rust-bin.mk   | 18 ++++++++++++++++--
 utils/update-rust              |  9 +++++++++
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/package/rust-bin/rust-bin.hash b/package/rust-bin/rust-bin.hash
index 7f9d2f6339..b49edb7580 100644
--- a/package/rust-bin/rust-bin.hash
+++ b/package/rust-bin/rust-bin.hash
@@ -1,6 +1,8 @@
 # Generated with utils/update-rust
 # Do not edit manually
 
+# From https://static.rust-lang.org/dist/rustc-1.88.0-src.tar.xz.sha256
+sha256  0c1dcbb4f762513d021e1a282c0ac58c0a423642b3a6bf581cafb5414df4193e  rustc-1.88.0-src.tar.xz
 # From https://static.rust-lang.org/dist/rust-1.88.0-aarch64-unknown-linux-gnu.tar.xz.sha256
 sha256  d5decc46123eb888f809f2ee3b118d13586a37ffad38afaefe56aa7139481d34  rust-1.88.0-aarch64-unknown-linux-gnu.tar.xz
 # From https://static.rust-lang.org/dist/rust-1.88.0-i686-unknown-linux-gnu.tar.xz.sha256
diff --git a/package/rust-bin/rust-bin.mk b/package/rust-bin/rust-bin.mk
index 215bd84ad3..2195584f8f 100644
--- a/package/rust-bin/rust-bin.mk
+++ b/package/rust-bin/rust-bin.mk
@@ -14,16 +14,19 @@ RUST_BIN_LICENSE_FILES = LICENSE-APACHE LICENSE-MIT
 HOST_RUST_BIN_PROVIDES = host-rustc
 
 HOST_RUST_BIN_SOURCE = rust-$(RUST_BIN_VERSION)-$(RUSTC_HOST_NAME).tar.xz
+HOST_RUST_BIN_SOURCE_TARBALL = rustc-$(RUST_BIN_VERSION)-src.tar.xz
+HOST_RUST_BIN_STD_TARBALLS =
 
 ifeq ($(BR2_PACKAGE_HOST_RUSTC_TARGET_ARCH_SUPPORTS),y)
-HOST_RUST_BIN_EXTRA_DOWNLOADS += rust-std-$(RUST_BIN_VERSION)-$(RUSTC_TARGET_NAME).tar.xz
+HOST_RUST_BIN_STD_TARBALLS += rust-std-$(RUST_BIN_VERSION)-$(RUSTC_TARGET_NAME).tar.xz
 endif
 
+HOST_RUST_BIN_EXTRA_DOWNLOADS += $(HOST_RUST_BIN_SOURCE_TARBALL) $(HOST_RUST_BIN_STD_TARBALLS)
 HOST_RUST_BIN_LIBSTD_HOST_PREFIX = rust-std-$(RUSTC_HOST_NAME)
 
 define HOST_RUST_BIN_LIBSTD_EXTRACT
 	mkdir -p $(@D)/std
-	$(foreach f,$(HOST_RUST_BIN_EXTRA_DOWNLOADS), \
+	$(foreach f,$(HOST_RUST_BIN_STD_TARBALLS), \
 		$(call suitable-extractor,$(f)) $(HOST_RUST_BIN_DL_DIR)/$(f) | \
 			$(TAR) -C $(@D)/std $(TAR_OPTIONS) -
 	)
@@ -61,4 +64,15 @@ endef
 
 HOST_RUST_BIN_POST_INSTALL_HOOKS += HOST_RUST_INSTALL_CARGO_CONFIG
 
+define HOST_RUST_BIN_EXTRACT_SRC_LIBRARY
+	mkdir -p $(@D)/rust-src
+	$(call suitable-extractor,$(HOST_RUST_BIN_SOURCE_TARBALL)) \
+	$(HOST_RUST_BIN_DL_DIR)/$(HOST_RUST_BIN_SOURCE_TARBALL) | \
+	$(TAR) -C $(@D)/rust-src --strip-components=1 $(TAR_OPTIONS) -
+	mkdir -p $(HOST_DIR)/lib/rustlib/src/rust
+	cp -a $(@D)/rust-src/library $(HOST_DIR)/lib/rustlib/src/rust/
+endef
+
+HOST_RUST_BIN_POST_EXTRACT_HOOKS += HOST_RUST_BIN_EXTRACT_SRC_LIBRARY
+
 $(eval $(host-generic-package))
diff --git a/utils/update-rust b/utils/update-rust
index 7db3feff9c..a1164db0d0 100755
--- a/utils/update-rust
+++ b/utils/update-rust
@@ -100,6 +100,15 @@ def gen_hash_file_src(hash_file, new_version):
 def gen_hash_file_bin(hash_file, new_version):
     with hash_file.open("w") as fd:
         fd.write("# Generated with utils/update-rust\n# Do not edit manually\n\n")
+        f_name = f"rustc-{new_version}-src.tar.xz"
+        print(f"\r\033[KUpdating {f_name}", end="")
+        h_url = f"{RUST_DIST_URL}/{f_name}.sha256"
+        with urllib.request.urlopen(h_url) as r:
+            if r.status != 200:
+                raise RuntimeError(f"No hash for {f_name}. Has source been removed?")
+            # rstrip() content, and explicitly add the \n, in case
+            # a hash file does not have a trailing \n.
+            fd.write(f"# From {h_url}\nsha256  {r.read().decode().rstrip()}\n")
         for host in RUST_HOSTS:
             f_name = f"rust-{new_version}-{host}.tar.xz"
             print(f"\r\033[KUpdating {f_name}", end="")
-- 
2.43.0

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[Buildroot] [RFC PATCH 3/5] package/rust-bin: install rustfmt

[El Mehdi YOUNES via buildroot]

Rust-for-Linux expects rustfmt to be available; otherwise the kernel
emits a "rustfmt not found" warning and the generated bindings are not
correct. Provide rustfmt from rust-bin by adding it to the installed
components.

Note: the dist tarball exposes the component as "rustfmt-preview"
(as listed in 'components' file), so we use that name.

Signed-off-by: El Mehdi YOUNES <elmehdi.younes@smile.fr>
---
 package/rust-bin/rust-bin.mk | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/package/rust-bin/rust-bin.mk b/package/rust-bin/rust-bin.mk
index 2195584f8f..75494fb286 100644
--- a/package/rust-bin/rust-bin.mk
+++ b/package/rust-bin/rust-bin.mk
@@ -43,7 +43,7 @@ HOST_RUST_BIN_INSTALL_COMMON_OPTS = \
 
 HOST_RUST_BIN_INSTALL_OPTS = \
 	$(HOST_RUST_BIN_INSTALL_COMMON_OPTS) \
-	--components=rustc,cargo,rust-std-$(RUSTC_HOST_NAME)
+	--components=rustc,cargo,rust-std-$(RUSTC_HOST_NAME),rustfmt-preview
 
 define HOST_RUST_BIN_INSTALL_RUSTC
 	(cd $(@D); \
-- 
2.43.0

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[Buildroot] [RFC PATCH 4/5] linux: split HOSTCC from flags

[El Mehdi YOUNES via buildroot]

Rust-for-Linux invokes rustc like:
  $(RUSTC_OR_CLIPPY) $(rust_common_flags) $(rustc_target_flags) \
    -Clinker-flavor=gcc -Clinker=$(HOSTCC) (see:
	https://github.com/torvalds/linux/blob/master/rust/Makefile#L407).

When Buildroot embeds flags into HOSTCC (e.g. HOSTCC="gcc <cflags> <ldflags>"),
rustc treats the entire value as the linker program name; and it fails.

This patch passes a clean HOSTCC and moves flags to the dedicated host-side
variables accepted by Kbuild:
  - HOSTCC      := $(HOSTCC)
  - HOSTCFLAGS  := $(subst -I/,-isystem /,$(subst -I /,-isystem /,$(HOST_CFLAGS)))
  - HOSTLDFLAGS := $(HOST_LDFLAGS)

Since Linux v4.19, Kbuild provides explicit variables for host flags, so splitting
compiler vs flags is supported upstream (see:
  https://github.com/torvalds/linux/commit/96f14fe738b69dd97a33efe3cc8ab330af5fd1f1
  https://github.com/torvalds/linux/commit/b90a368000abe5e015e0b045ca2ff7c2173b94c0
  https://github.com/torvalds/linux/commit/f92d19e0ef9bbbb2984845682e740934ad45473b).

But with this change we can have problems with older kernel versions
(< 4.19), as the Buildroot commit below warned when avoiding HOSTCFLAGS
to not override internal kernel flags:
  https://gitlab.com/buildroot.org/buildroot/-/commit/dde090c299b0357fdb1a4ec44ad8d332ac57f65e

Signed-off-by: El Mehdi YOUNES <elmehdi.younes@smile.fr>
---
I’m aware this split is currently needed only for Rust-for-Linux (which targets
>= 6.1). I considered adding a version-based condition, but I’m not sure about
the best way to express that in Buildroot, or if there’s a better approach to
avoid regressions on pre-4.19 kernels. I’m requesting ideas/guidance
on how you’d like this to be gated.

Signed-off-by: El Mehdi YOUNES <elmehdi.younes@smile.fr>
---
 linux/linux.mk | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/linux/linux.mk b/linux/linux.mk
index 0520394931..f5ac64fdd2 100644
--- a/linux/linux.mk
+++ b/linux/linux.mk
@@ -161,7 +161,9 @@ endif
 # Disable building host tools with -Werror: newer gcc versions can be
 # extra picky about some code (https://bugs.busybox.net/show_bug.cgi?id=14826)
 LINUX_MAKE_FLAGS = \
-	HOSTCC="$(HOSTCC) $(subst -I/,-isystem /,$(subst -I /,-isystem /,$(HOST_CFLAGS))) $(HOST_LDFLAGS)" \
+	HOSTCC="$(HOSTCC)" \
+	HOSTCFLAGS="$(subst -I/,-isystem /,$(subst -I /,-isystem /,$(HOST_CFLAGS)))" \
+	HOSTLDFLAGS="$(HOST_LDFLAGS)" \
 	ARCH=$(KERNEL_ARCH) \
 	KCFLAGS="$(LINUX_CFLAGS)" \
 	INSTALL_MOD_PATH=$(TARGET_DIR) \
-- 
2.43.0

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[Buildroot] [RFC PATCH 5/5] linux: Add Rust support

[El Mehdi YOUNES via buildroot]

Add a menu option to enable Rust-for-Linux from Buildroot. When
BR2_LINUX_KERNEL_RUST_SUPPORT=y, select the required host tools and pass
them to the kernel build:

  - Dependencies: host-rustc, host-rust-bindgen
  - Make vars: RUSTC, BINDGEN, RUST_LIB_SRC, LIBCLANG_PATH, RUSTFMT
  - Kconfig fixup: force CONFIG_RUST=y, since all prerequisites are now
    provided by the above variables/paths

Signed-off-by: El Mehdi YOUNES <elmehdi.younes@smile.fr>
---
 linux/Config.in |  6 ++++++
 linux/linux.mk  | 12 ++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/linux/Config.in b/linux/Config.in
index 7f90c566b0..86525c9b0a 100644
--- a/linux/Config.in
+++ b/linux/Config.in
@@ -557,6 +557,12 @@ config BR2_LINUX_KERNEL_NEEDS_HOST_PYTHON3
 	  Enable this option if you get a Linux kernel build failure
 	  such as "python3: not found".
 
+config BR2_LINUX_KERNEL_RUST_SUPPORT
+	bool "Enable Rust support in the kernel"
+	depends on BR2_PACKAGE_HOST_RUSTC_TARGET_ARCH_SUPPORTS
+	select BR2_PACKAGE_HOST_RUSTC
+	select BR2_PACKAGE_HOST_RUST_BINDGEN
+
 # Linux extensions
 source "linux/Config.ext.in"
 
diff --git a/linux/linux.mk b/linux/linux.mk
index f5ac64fdd2..d95356342b 100644
--- a/linux/linux.mk
+++ b/linux/linux.mk
@@ -180,6 +180,16 @@ LINUX_MAKE_ENV += \
 	KBUILD_BUILD_TIMESTAMP="$(shell LC_ALL=C TZ='UTC' date -d @$(SOURCE_DATE_EPOCH))"
 endif
 
+ifeq ($(BR2_LINUX_KERNEL_RUST_SUPPORT),y)
+LINUX_DEPENDENCIES += host-rustc host-rust-bindgen
+LINUX_MAKE_FLAGS += \
+	RUSTC=$(HOST_DIR)/bin/rustc \
+	BINDGEN=$(HOST_DIR)/bin/bindgen \
+	RUST_LIB_SRC=$(HOST_DIR)/lib/rustlib/src/rust/library \
+	LIBCLANG_PATH=$(HOST_DIR)/lib \
+	RUSTFMT=$(HOST_DIR)/bin/rustfmt
+endif
+
 # gcc-8 started warning about function aliases that have a
 # non-matching prototype.  This seems rather useful in general, but it
 # causes tons of warnings in the Linux kernel, where we rely on
@@ -479,6 +489,8 @@ define LINUX_KCONFIG_FIXUP_CMDS
 		$(call KCONFIG_ENABLE_OPT,CONFIG_FB)
 		$(call KCONFIG_ENABLE_OPT,CONFIG_LOGO)
 		$(call KCONFIG_ENABLE_OPT,CONFIG_LOGO_LINUX_CLUT224))
+	$(if $(BR2_LINUX_KERNEL_RUST_SUPPORT),
+		$(call KCONFIG_ENABLE_OPT,CONFIG_RUST))
 	$(call KCONFIG_DISABLE_OPT,CONFIG_GCC_PLUGINS)
 	$(call KCONFIG_DISABLE_OPT,CONFIG_WERROR)
 	$(PACKAGES_LINUX_CONFIG_FIXUPS)
-- 
2.43.0

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Re: [Buildroot] [RFC PATCH 1/5] package/rust-bindgen: add host-clang dependency

[Thomas Petazzoni via buildroot]

Hello Mehdi,

Sorry for the long delay in getting back to you!

On Fri, Aug 08, 2025 at 03:31:08PM +0200, El Mehdi YOUNES via buildroot wrote:
> According to the official requirements, bindgen needs libclang to
> parse C/C++ headers. Until now the tool was used mainly by Mesa and
> worked, but Rust-for-Linux explicitly relies on bindgen + libclang,
> otherwise we can't activate Rust for linux.
> 
> See
> https://rust-lang.github.io/rust-bindgen/requirements.html
> 
> Signed-off-by: El Mehdi YOUNES <elmehdi.younes@smile.fr>

We have finally applied your patch! However, we improved the commit
log to clarify further what happens, why it worked today without any
issue, and we also added a comment in .mk explaining why we use a
build time dependency for what really is a run-time dependency.

See:

 https://gitlab.com/buildroot.org/buildroot/-/commit/34ed3bbf0a5f2576043ff627c76df584ea936a71

for the final commit.

Thanks a lot!

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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Re: [Buildroot] [RFC PATCH 2/5] package/rust-bin: add Rust sources

[Thomas Petazzoni via buildroot]

Hello,

Thanks for this patch, and sorry for the delay in reviewing
it. Generally the approach looks good, but we have a few comments, see
below.

On Fri, Aug 08, 2025 at 03:31:09PM +0200, El Mehdi YOUNES via buildroot wrote:
> Rust-for-Linux requires the Rust standard library sources (e.g. core/lib.rs)
> to enable CONFIG_RUST. This patch provides them in rust-bin while keeping the
> prebuilt compiler tarball unchanged.
> 
> It adds HOST_RUST_BIN_SOURCE_TARBALL = rustc-$(VER)-src.tar.xz to
> HOST_RUST_BIN_EXTRA_DOWNLOADS, and splits extra downloads into
> HOST_RUST_BIN_STD_TARBALLS (rust-std-*) and HOST_RUST_BIN_SOURCE_TARBALL so
> extraction is controlled separately: rust-std-* are unpacked under $(@D)/std,
> and rustc-<ver>-src.tar.xz is unpacked to rust-src then only the 'library/'
> subtree from the source tarball is installed $(HOST_DIR)/lib/rustlib/src/rust/.
> 
> The utils/update-rust script is also extended to generate the sha256 line for
> rustc-<ver>-src.tar.xz in package/rust-bin/rust-bin.hash.
> 
> see
> https://github.com/torvalds/linux/blob/master/Documentation/rust/quick-start.rst
> 
> Signed-off-by: El Mehdi YOUNES <elmehdi.younes@smile.fr>
> ---
>  package/rust-bin/rust-bin.hash |  2 ++
>  package/rust-bin/rust-bin.mk   | 18 ++++++++++++++++--
>  utils/update-rust              |  9 +++++++++
>  3 files changed, 27 insertions(+), 2 deletions(-)

First of all, fixing package/rust-bin is not sufficient, you also need
to ensure that package/rust does the right thing. Indeed, we have two
ways of proving the Rust compiler in Buildroot: using a pre-compiled
Rust compiler (package/rust-bin) or building the Rust compiler from
source (package/rust). The Rust support in Linux should work for both
cases.

> diff --git a/package/rust-bin/rust-bin.mk b/package/rust-bin/rust-bin.mk
> index 215bd84ad3..2195584f8f 100644
> --- a/package/rust-bin/rust-bin.mk
> +++ b/package/rust-bin/rust-bin.mk
> @@ -14,16 +14,19 @@ RUST_BIN_LICENSE_FILES = LICENSE-APACHE LICENSE-MIT
>  HOST_RUST_BIN_PROVIDES = host-rustc
>  
>  HOST_RUST_BIN_SOURCE = rust-$(RUST_BIN_VERSION)-$(RUSTC_HOST_NAME).tar.xz
> +HOST_RUST_BIN_SOURCE_TARBALL = rustc-$(RUST_BIN_VERSION)-src.tar.xz
> +HOST_RUST_BIN_STD_TARBALLS =

Setting to an empty variable is not really needed.

>  
>  ifeq ($(BR2_PACKAGE_HOST_RUSTC_TARGET_ARCH_SUPPORTS),y)
> -HOST_RUST_BIN_EXTRA_DOWNLOADS += rust-std-$(RUST_BIN_VERSION)-$(RUSTC_TARGET_NAME).tar.xz
> +HOST_RUST_BIN_STD_TARBALLS += rust-std-$(RUST_BIN_VERSION)-$(RUSTC_TARGET_NAME).tar.xz

This could be just a = sign.

>  endif
>  
> +HOST_RUST_BIN_EXTRA_DOWNLOADS += $(HOST_RUST_BIN_SOURCE_TARBALL) $(HOST_RUST_BIN_STD_TARBALLS)
>  HOST_RUST_BIN_LIBSTD_HOST_PREFIX = rust-std-$(RUSTC_HOST_NAME)
>  
>  define HOST_RUST_BIN_LIBSTD_EXTRACT
>  	mkdir -p $(@D)/std
> -	$(foreach f,$(HOST_RUST_BIN_EXTRA_DOWNLOADS), \
> +	$(foreach f,$(HOST_RUST_BIN_STD_TARBALLS), \

The change from HOST_RUST_BIN_EXTRA_DOWNLOADS to
HOST_RUST_BIN_STD_TARBALLS could actually go in a separate,
preparatory commit. It would make the commit adding the installation
of Rust sources shorter and simpler to review.

>  		$(call suitable-extractor,$(f)) $(HOST_RUST_BIN_DL_DIR)/$(f) | \
>  			$(TAR) -C $(@D)/std $(TAR_OPTIONS) -
>  	)
> @@ -61,4 +64,15 @@ endef
>  
>  HOST_RUST_BIN_POST_INSTALL_HOOKS += HOST_RUST_INSTALL_CARGO_CONFIG
>  
> +define HOST_RUST_BIN_EXTRACT_SRC_LIBRARY
> +	mkdir -p $(@D)/rust-src
> +	$(call suitable-extractor,$(HOST_RUST_BIN_SOURCE_TARBALL)) \
> +	$(HOST_RUST_BIN_DL_DIR)/$(HOST_RUST_BIN_SOURCE_TARBALL) | \
> +	$(TAR) -C $(@D)/rust-src --strip-components=1 $(TAR_OPTIONS) -

Please indent follow-up lines, as such:

	$(call suitable-extractor,$(HOST_RUST_BIN_SOURCE_TARBALL)) \
	       $(HOST_RUST_BIN_DL_DIR)/$(HOST_RUST_BIN_SOURCE_TARBALL) | \
	       $(TAR) -C $(@D)/rust-src --strip-components=1 $(TAR_OPTIONS) -

so that's it's clearly visible it's the same command.

> +	mkdir -p $(HOST_DIR)/lib/rustlib/src/rust
> +	cp -a $(@D)/rust-src/library $(HOST_DIR)/lib/rustlib/src/rust/

Can we install in $(HOST_DIR)/src/rust for example? In PATCH 5/5,
you're anyway passing explicitly the path to the Rust source code.

Or do we need to use $(HOST_DIR)/lib/rustlib/src/rust/ because in the
package/rust case (where we build the compiler ourselves), the source
gets installed there automatically?

Could you fixup those issues and submit an updated version?

Thanks a lot!

Thomas
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Re: [Buildroot] [RFC PATCH 3/5] package/rust-bin: install rustfmt

[Thomas Petazzoni via buildroot]

Hello Mehdi,

On Fri, Aug 08, 2025 at 03:31:10PM +0200, El Mehdi YOUNES via buildroot wrote:
> Rust-for-Linux expects rustfmt to be available; otherwise the kernel
> emits a "rustfmt not found" warning and the generated bindings are not
> correct. Provide rustfmt from rust-bin by adding it to the installed
> components.
> 
> Note: the dist tarball exposes the component as "rustfmt-preview"
> (as listed in 'components' file), so we use that name.
> 
> Signed-off-by: El Mehdi YOUNES <elmehdi.younes@smile.fr>

Thanks for the patch. Here as well, you not only have to adjust
package/rust-bin, but also package/rust, so that package/rust also
installs rustfmt.

Could you have a look into this, and send an updated version?

Thanks a lot!

Thomas
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Re: [Buildroot] [RFC PATCH 4/5] linux: split HOSTCC from flags

[Thomas Petazzoni via buildroot]

Hello Mehdi,

Thanks for your patch!

On Fri, Aug 08, 2025 at 03:31:11PM +0200, El Mehdi YOUNES via buildroot wrote:

> Since Linux v4.19, Kbuild provides explicit variables for host flags, so splitting
> compiler vs flags is supported upstream (see:
>   https://github.com/torvalds/linux/commit/96f14fe738b69dd97a33efe3cc8ab330af5fd1f1
>   https://github.com/torvalds/linux/commit/b90a368000abe5e015e0b045ca2ff7c2173b94c0
>   https://github.com/torvalds/linux/commit/f92d19e0ef9bbbb2984845682e740934ad45473b).
> 
> But with this change we can have problems with older kernel versions
> (< 4.19), as the Buildroot commit below warned when avoiding HOSTCFLAGS
> to not override internal kernel flags:
>   https://gitlab.com/buildroot.org/buildroot/-/commit/dde090c299b0357fdb1a4ec44ad8d332ac57f65e

Since your change as-is would break Linux < 4.19, here is the
suggestion that we have after discussing at the Buildroot Developers
Meeting: make things condition based on
BR2_LINUX_KERNEL_RUST_SUPPORT. Something along the lines of:

ifeq ($(BR2_LINUX_KERNEL_RUST_SUPPORT),y)
LINUX_MAKE_FLAGS += \
	HOSTCC="$(HOSTCC)" \
	HOSTCFLAGS="$(subst -I/,-isystem /,$(subst -I /,-isystem /,$(HOST_CFLAGS)))" \
	HOSTLDFLAGS="$(HOST_LDFLAGS)"
else
LINUX_MAKE_FLAGS += \
	HOSTCC="$(HOSTCC) $(subst -I/,-isystem /,$(subst -I /,-isystem /,$(HOST_CFLAGS))) $(HOST_LDFLAGS)"
endif

Of course, if someone enables BR2_LINUX_KERNEL_RUST_SUPPORT with a
kernel < 4.19 it would fail to build, but that's acceptable as it's
stupid to do this since Linux 4.19 did not have any Rust support.

Thanks!

Thomas
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Re: [Buildroot] [RFC PATCH 5/5] linux: Add Rust support

[Thomas Petazzoni via buildroot]

On Fri, Aug 08, 2025 at 03:31:12PM +0200, El Mehdi YOUNES via buildroot wrote:

> +ifeq ($(BR2_LINUX_KERNEL_RUST_SUPPORT),y)
> +LINUX_DEPENDENCIES += host-rustc host-rust-bindgen
> +LINUX_MAKE_FLAGS += \
> +	RUSTC=$(HOST_DIR)/bin/rustc \
> +	BINDGEN=$(HOST_DIR)/bin/bindgen \
> +	RUST_LIB_SRC=$(HOST_DIR)/lib/rustlib/src/rust/library \

You'll have to update this to $(HOST_DIR)/src/rust if that ends up
working (see our comments on PATCH 2/5).

Make sure to test this with both pre-compiled Rust compiler and
compiled-from-source Rust compiler.

And finally, we would like to have a test in support/testing/ to
verify that this continues to work. You don't need a test that boots
the kernel, but at least something that builds the kernel with Rust
support. Of course if there's some HW-agnostic kernel feature in Rust
that we can test in Qemu, it would be nice. Maybe binder? But I'm not
sure how to use it under a pure Linux system. But don't spend too much
time on this: a compile-time only test will be good enough.

Thanks a lot!

Thomas
-- 
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Re: [Buildroot] [RFC PATCH 2/5] package/rust-bin: add Rust sources

[El Mehdi YOUNES via buildroot]

Hi Thomas,

On 2/3/26 14:33, Thomas Petazzoni wrote:
> Hello,
>
> Thanks for this patch, and sorry for the delay in reviewing
> it. Generally the approach looks good, but we have a few comments, see
> below.
>
> On Fri, Aug 08, 2025 at 03:31:09PM +0200, El Mehdi YOUNES via buildroot wrote:
>> Rust-for-Linux requires the Rust standard library sources (e.g. core/lib.rs)
>> to enable CONFIG_RUST. This patch provides them in rust-bin while keeping the
>> prebuilt compiler tarball unchanged.
>>
>> It adds HOST_RUST_BIN_SOURCE_TARBALL = rustc-$(VER)-src.tar.xz to
>> HOST_RUST_BIN_EXTRA_DOWNLOADS, and splits extra downloads into
>> HOST_RUST_BIN_STD_TARBALLS (rust-std-*) and HOST_RUST_BIN_SOURCE_TARBALL so
>> extraction is controlled separately: rust-std-* are unpacked under $(@D)/std,
>> and rustc-<ver>-src.tar.xz is unpacked to rust-src then only the 'library/'
>> subtree from the source tarball is installed $(HOST_DIR)/lib/rustlib/src/rust/.
>>
>> The utils/update-rust script is also extended to generate the sha256 line for
>> rustc-<ver>-src.tar.xz in package/rust-bin/rust-bin.hash.
>>
>> see
>> https://github.com/torvalds/linux/blob/master/Documentation/rust/quick-start.rst
>>
>> Signed-off-by: El Mehdi YOUNES <elmehdi.younes@smile.fr>
>> ---
>>   package/rust-bin/rust-bin.hash |  2 ++
>>   package/rust-bin/rust-bin.mk   | 18 ++++++++++++++++--
>>   utils/update-rust              |  9 +++++++++
>>   3 files changed, 27 insertions(+), 2 deletions(-)
> First of all, fixing package/rust-bin is not sufficient, you also need
> to ensure that package/rust does the right thing. Indeed, we have two
> ways of proving the Rust compiler in Buildroot: using a pre-compiled
> Rust compiler (package/rust-bin) or building the Rust compiler from
> source (package/rust). The Rust support in Linux should work for both
> cases.

Thanks a lot for the feedback, this series was first sent only for feedback,

the change only for rust-bin was in purpose to facilitate testing and 
have some

feedback before the final patch.

I will add it on a v2

>> diff --git a/package/rust-bin/rust-bin.mk b/package/rust-bin/rust-bin.mk
>> index 215bd84ad3..2195584f8f 100644
>> --- a/package/rust-bin/rust-bin.mk
>> +++ b/package/rust-bin/rust-bin.mk
>> @@ -14,16 +14,19 @@ RUST_BIN_LICENSE_FILES = LICENSE-APACHE LICENSE-MIT
>>   HOST_RUST_BIN_PROVIDES = host-rustc
>>   
>>   HOST_RUST_BIN_SOURCE = rust-$(RUST_BIN_VERSION)-$(RUSTC_HOST_NAME).tar.xz
>> +HOST_RUST_BIN_SOURCE_TARBALL = rustc-$(RUST_BIN_VERSION)-src.tar.xz
>> +HOST_RUST_BIN_STD_TARBALLS =
> Setting to an empty variable is not really needed.
>
>>   
>>   ifeq ($(BR2_PACKAGE_HOST_RUSTC_TARGET_ARCH_SUPPORTS),y)
>> -HOST_RUST_BIN_EXTRA_DOWNLOADS += rust-std-$(RUST_BIN_VERSION)-$(RUSTC_TARGET_NAME).tar.xz
>> +HOST_RUST_BIN_STD_TARBALLS += rust-std-$(RUST_BIN_VERSION)-$(RUSTC_TARGET_NAME).tar.xz
> This could be just a = sign.
>
>>   endif
>>   
>> +HOST_RUST_BIN_EXTRA_DOWNLOADS += $(HOST_RUST_BIN_SOURCE_TARBALL) $(HOST_RUST_BIN_STD_TARBALLS)
>>   HOST_RUST_BIN_LIBSTD_HOST_PREFIX = rust-std-$(RUSTC_HOST_NAME)
>>   
>>   define HOST_RUST_BIN_LIBSTD_EXTRACT
>>   	mkdir -p $(@D)/std
>> -	$(foreach f,$(HOST_RUST_BIN_EXTRA_DOWNLOADS), \
>> +	$(foreach f,$(HOST_RUST_BIN_STD_TARBALLS), \
> The change from HOST_RUST_BIN_EXTRA_DOWNLOADS to
> HOST_RUST_BIN_STD_TARBALLS could actually go in a separate,
> preparatory commit. It would make the commit adding the installation
> of Rust sources shorter and simpler to review.
>
>>   		$(call suitable-extractor,$(f)) $(HOST_RUST_BIN_DL_DIR)/$(f) | \
>>   			$(TAR) -C $(@D)/std $(TAR_OPTIONS) -
>>   	)
>> @@ -61,4 +64,15 @@ endef
>>   
>>   HOST_RUST_BIN_POST_INSTALL_HOOKS += HOST_RUST_INSTALL_CARGO_CONFIG
>>   
>> +define HOST_RUST_BIN_EXTRACT_SRC_LIBRARY
>> +	mkdir -p $(@D)/rust-src
>> +	$(call suitable-extractor,$(HOST_RUST_BIN_SOURCE_TARBALL)) \
>> +	$(HOST_RUST_BIN_DL_DIR)/$(HOST_RUST_BIN_SOURCE_TARBALL) | \
>> +	$(TAR) -C $(@D)/rust-src --strip-components=1 $(TAR_OPTIONS) -
> Please indent follow-up lines, as such:
>
> 	$(call suitable-extractor,$(HOST_RUST_BIN_SOURCE_TARBALL)) \
> 	       $(HOST_RUST_BIN_DL_DIR)/$(HOST_RUST_BIN_SOURCE_TARBALL) | \
> 	       $(TAR) -C $(@D)/rust-src --strip-components=1 $(TAR_OPTIONS) -
>
> so that's it's clearly visible it's the same command.
>
>> +	mkdir -p $(HOST_DIR)/lib/rustlib/src/rust
>> +	cp -a $(@D)/rust-src/library $(HOST_DIR)/lib/rustlib/src/rust/
> Can we install in $(HOST_DIR)/src/rust for example? In PATCH 5/5,
> you're anyway passing explicitly the path to the Rust source code.
>
> Or do we need to use $(HOST_DIR)/lib/rustlib/src/rust/ because in the
> package/rust case (where we build the compiler ourselves), the source
> gets installed there automatically?
>
> Could you fixup those issues and submit an updated version?

Thank you so mush for the feedback, I will fix.

I'll try to send a v2 on the next days

>
> Thanks a lot!
>
> Thomas
Best regards,
El Mehdi
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Re: [Buildroot] [RFC PATCH 3/5] package/rust-bin: install rustfmt

[El Mehdi YOUNES via buildroot]

On 2/3/26 14:35, Thomas Petazzoni wrote:
> Hello Mehdi,
>
> On Fri, Aug 08, 2025 at 03:31:10PM +0200, El Mehdi YOUNES via buildroot wrote:
>> Rust-for-Linux expects rustfmt to be available; otherwise the kernel
>> emits a "rustfmt not found" warning and the generated bindings are not
>> correct. Provide rustfmt from rust-bin by adding it to the installed
>> components.
>>
>> Note: the dist tarball exposes the component as "rustfmt-preview"
>> (as listed in 'components' file), so we use that name.
>>
>> Signed-off-by: El Mehdi YOUNES <elmehdi.younes@smile.fr>
> Thanks for the patch. Here as well, you not only have to adjust
> package/rust-bin, but also package/rust, so that package/rust also
> installs rustfmt.
>
> Could you have a look into this, and send an updated version?
Thanks, It will be added on the v2
>
> Thanks a lot!
>
> Thomas

Best regards,

El Mehdi

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Re: [Buildroot] [RFC PATCH 4/5] linux: split HOSTCC from flags

[El Mehdi YOUNES via buildroot]

Hi Thomas,

On 2/3/26 14:50, Thomas Petazzoni wrote:
> Hello Mehdi,
>
> Thanks for your patch!
>
> On Fri, Aug 08, 2025 at 03:31:11PM +0200, El Mehdi YOUNES via buildroot wrote:
>
>> Since Linux v4.19, Kbuild provides explicit variables for host flags, so splitting
>> compiler vs flags is supported upstream (see:
>>    https://github.com/torvalds/linux/commit/96f14fe738b69dd97a33efe3cc8ab330af5fd1f1
>>    https://github.com/torvalds/linux/commit/b90a368000abe5e015e0b045ca2ff7c2173b94c0
>>    https://github.com/torvalds/linux/commit/f92d19e0ef9bbbb2984845682e740934ad45473b).
>>
>> But with this change we can have problems with older kernel versions
>> (< 4.19), as the Buildroot commit below warned when avoiding HOSTCFLAGS
>> to not override internal kernel flags:
>>    https://gitlab.com/buildroot.org/buildroot/-/commit/dde090c299b0357fdb1a4ec44ad8d332ac57f65e
> Since your change as-is would break Linux < 4.19, here is the
> suggestion that we have after discussing at the Buildroot Developers
> Meeting: make things condition based on
> BR2_LINUX_KERNEL_RUST_SUPPORT. Something along the lines of:
>
> ifeq ($(BR2_LINUX_KERNEL_RUST_SUPPORT),y)
> LINUX_MAKE_FLAGS += \
> 	HOSTCC="$(HOSTCC)" \
> 	HOSTCFLAGS="$(subst -I/,-isystem /,$(subst -I /,-isystem /,$(HOST_CFLAGS)))" \
> 	HOSTLDFLAGS="$(HOST_LDFLAGS)"
> else
> LINUX_MAKE_FLAGS += \
> 	HOSTCC="$(HOSTCC) $(subst -I/,-isystem /,$(subst -I /,-isystem /,$(HOST_CFLAGS))) $(HOST_LDFLAGS)"
> endif

Thank you for the suggestion, I will add it on the next version

>
> Of course, if someone enables BR2_LINUX_KERNEL_RUST_SUPPORT with a
> kernel < 4.19 it would fail to build, but that's acceptable as it's
> stupid to do this since Linux 4.19 did not have any Rust support.
>
> Thanks!
>
> Thomas

Best regards,

El Mehdi

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Re: [Buildroot] [RFC PATCH 5/5] linux: Add Rust support

[El Mehdi YOUNES via buildroot]

On 2/3/26 15:08, Thomas Petazzoni wrote:
> On Fri, Aug 08, 2025 at 03:31:12PM +0200, El Mehdi YOUNES via buildroot wrote:
>
>> +ifeq ($(BR2_LINUX_KERNEL_RUST_SUPPORT),y)
>> +LINUX_DEPENDENCIES += host-rustc host-rust-bindgen
>> +LINUX_MAKE_FLAGS += \
>> +	RUSTC=$(HOST_DIR)/bin/rustc \
>> +	BINDGEN=$(HOST_DIR)/bin/bindgen \
>> +	RUST_LIB_SRC=$(HOST_DIR)/lib/rustlib/src/rust/library \
> You'll have to update this to $(HOST_DIR)/src/rust if that ends up
> working (see our comments on PATCH 2/5).
>
> Make sure to test this with both pre-compiled Rust compiler and
> compiled-from-source Rust compiler.
I will improve it on v2, Thanks a lot!
>
> And finally, we would like to have a test in support/testing/ to
> verify that this continues to work. You don't need a test that boots
> the kernel, but at least something that builds the kernel with Rust
> support. Of course if there's some HW-agnostic kernel feature in Rust
> that we can test in Qemu, it would be nice. Maybe binder? But I'm not
> sure how to use it under a pure Linux system. But don't spend too much
> time on this: a compile-time only test will be good enough.

Maybe we can add a runtime test using the rust_minimal sample.

https://github.com/torvalds/linux/blob/master/samples/rust/rust_minimal.rs

I have already tested it on Qemu, so I will try to add a runtime test 
using it.

I will add it to the v2.

>
> Thanks a lot!
>
> Thomas

Best regards,

El Mehdi

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Re: [Buildroot] [RFC PATCH 5/5] linux: Add Rust support

[Thomas Petazzoni via buildroot]

Hello,

On Tue, Feb 03, 2026 at 03:34:48PM +0100, El Mehdi YOUNES wrote:

> Maybe we can add a runtime test using the rust_minimal sample.
> 
> https://github.com/torvalds/linux/blob/master/samples/rust/rust_minimal.rs
> 
> I have already tested it on Qemu, so I will try to add a runtime test using
> it.

Very good idea!

Thomas
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Re: [Buildroot] [RFC PATCH 1/5] package/rust-bindgen: add host-clang dependency

[Thomas Perale via buildroot]

In reply of:
> According to the official requirements, bindgen needs libclang to
> parse C/C++ headers. Until now the tool was used mainly by Mesa and
> worked, but Rust-for-Linux explicitly relies on bindgen + libclang,
> otherwise we can't activate Rust for linux.
> 
> See
> https://rust-lang.github.io/rust-bindgen/requirements.html
> 
> Signed-off-by: El Mehdi YOUNES <elmehdi.younes@smile.fr>

Applied to 2025.02.x & 2025.11.x. Thanks

> ---
>  package/rust-bindgen/rust-bindgen.mk | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/package/rust-bindgen/rust-bindgen.mk b/package/rust-bindgen/rust-bindgen.mk
> index 349d4c3670..0ec620002a 100644
> --- a/package/rust-bindgen/rust-bindgen.mk
> +++ b/package/rust-bindgen/rust-bindgen.mk
> @@ -9,6 +9,8 @@ RUST_BINDGEN_SITE = $(call github,rust-lang,rust-bindgen,v$(RUST_BINDGEN_VERSION
>  RUST_BINDGEN_LICENSE = BSD-3-clause
>  RUST_BINDGEN_LICENSE_FILES = LICENSE
>  
> +HOST_RUST_BINDGEN_DEPENDENCIES = host-clang
> +
>  # The Cargo.toml at the root directory is a "virtual manifest".
>  # Since we only want to build and install bindgen use the Cargo.toml
>  # from the bindgen-cli subdirectory.
> -- 
> 2.43.0
> 
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