kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 182 insertions, 0 deletions

diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
new file mode 100644
index 000000000..c49ab9106
--- /dev/null
+++ b/samples/rust/Kconfig
@@ -0,0 +1,182 @@
+# SPDX-License-Identifier: GPL-2.0
+
+menuconfig SAMPLES_RUST
+	bool "Rust samples"
+	depends on RUST
+	help
+	  You can build sample Rust kernel code here.
+
+	  If unsure, say N.
+
+if SAMPLES_RUST
+
+config SAMPLE_RUST_CONFIGFS
+	tristate "Configfs sample"
+	depends on CONFIGFS_FS
+	help
+	  This option builds the Rust configfs sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_configfs.
+
+	  If unsure, say N.
+
+config SAMPLE_RUST_MINIMAL
+	tristate "Minimal"
+	help
+	  This option builds the Rust minimal module sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_minimal.
+
+	  If unsure, say N.
+
+config SAMPLE_RUST_MISC_DEVICE
+	tristate "Misc device"
+	help
+	  This option builds the Rust misc device.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_misc_device.
+
+	  If unsure, say N.
+
+config SAMPLE_RUST_PRINT
+	tristate "Printing macros"
+	help
+	  This option builds the Rust printing macros sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_print.
+
+	  If unsure, say N.
+
+config SAMPLE_RUST_DMA
+	tristate "DMA Test Driver"
+	depends on PCI
+	help
+	  This option builds the Rust DMA Test driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_dma.
+
+	  If unsure, say N.
+
+config SAMPLE_RUST_DEBUGFS
+	tristate "DebugFS Test Module"
+	depends on DEBUG_FS
+	help
+	  This option builds the Rust DebugFS Test module sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_debugfs.
+
+	  If unsure, say N.
+
+config SAMPLE_RUST_DEBUGFS_SCOPED
+	tristate "Scoped DebugFS Test Module"
+	depends on DEBUG_FS
+	help
+	  This option builds the Rust Scoped DebugFS Test module sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_debugfs_scoped.
+
+	  If unsure, say N.
+
+config SAMPLE_RUST_DRIVER_I2C
+	tristate "I2C Driver"
+	depends on I2C=y
+	help
+	  This option builds the Rust I2C driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_driver_i2c.
+
+	  If unsure, say N.
+
+config SAMPLE_RUST_I2C_CLIENT
+	tristate "I2C Client Registration"
+	depends on I2C=y
+	help
+	  This option builds the Rust I2C client manual creation
+	  sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_i2c_client.
+
+	  If unsure, say N.
+
+config SAMPLE_RUST_DRIVER_PCI
+	tristate "PCI Driver"
+	depends on PCI
+	help
+	  This option builds the Rust PCI driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_driver_pci.
+
+	  If unsure, say N.
+
+config SAMPLE_RUST_DRIVER_PLATFORM
+	tristate "Platform Driver"
+	help
+	  This option builds the Rust Platform driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_driver_platform.
+
+	  If unsure, say N.
+
+config SAMPLE_RUST_DRIVER_USB
+	tristate "USB Driver"
+	depends on USB = y
+	help
+	  This option builds the Rust USB driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_driver_usb.
+
+	  If unsure, say N.
+
+config SAMPLE_RUST_DRIVER_FAUX
+	tristate "Faux Driver"
+	help
+	  This option builds the Rust Faux driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_driver_faux.
+
+	  If unsure, say N.
+
+config SAMPLE_RUST_DRIVER_AUXILIARY
+	tristate "Auxiliary Driver"
+	depends on PCI
+	select AUXILIARY_BUS
+	help
+	  This option builds the Rust auxiliary driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_driver_auxiliary.
+
+	  If unsure, say N.
+
+config SAMPLE_RUST_SOC
+	tristate "SoC Driver"
+	select SOC_BUS
+	help
+	  This option builds the Rust SoC driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_soc.
+
+	  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