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, 150 insertions, 0 deletions

diff --git a/drivers/counter/Kconfig b/drivers/counter/Kconfig
new file mode 100644
index 000000000..d30d22dfe
--- /dev/null
+++ b/drivers/counter/Kconfig
@@ -0,0 +1,150 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# Counter devices
+#
+
+config I8254
+	tristate
+	select COUNTER
+	select REGMAP
+	help
+	  Enables support for the i8254 interface library functions. The i8254
+	  interface library provides functions to facilitate communication with
+	  interfaces compatible with the venerable Intel 8254 Programmable
+	  Interval Timer (PIT). The Intel 825x family of chips was first
+	  released in the early 1980s but compatible interfaces are nowadays
+	  typically found embedded in larger VLSI processing chips and FPGA
+	  components.
+
+	  If built as a module its name will be i8254.
+
+menuconfig COUNTER
+	tristate "Counter support"
+	help
+	  This enables counter device support through the Generic Counter
+	  interface. You only need to enable this, if you also want to enable
+	  one or more of the counter device drivers below.
+
+if COUNTER
+
+config 104_QUAD_8
+	tristate "ACCES 104-QUAD-8 driver"
+	depends on (PC104 && X86) || COMPILE_TEST
+	depends on HAS_IOPORT_MAP
+	select ISA_BUS_API
+	select REGMAP_MMIO
+	help
+	  Say yes here to build support for the ACCES 104-QUAD-8 quadrature
+	  encoder counter/interface device family (104-QUAD-8, 104-QUAD-4).
+
+	  A counter's respective error flag may be cleared by performing a write
+	  operation on the respective count value attribute. The 104-QUAD-8
+	  counters may be set either directly or via the counter's preset
+	  attribute.
+
+	  The base port addresses for the devices may be configured via the base
+	  array module parameter. The interrupt line numbers for the devices may
+	  be configured via the irq array module parameter.
+
+config FTM_QUADDEC
+	tristate "Flex Timer Module Quadrature decoder driver"
+	depends on SOC_LS1021A || COMPILE_TEST
+	depends on HAS_IOMEM && OF
+	help
+	  Select this option to enable the Flex Timer Quadrature decoder
+	  driver.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called ftm-quaddec.
+
+config INTEL_QEP
+	tristate "Intel Quadrature Encoder Peripheral driver"
+	depends on X86
+	depends on PCI
+	help
+	  Select this option to enable the Intel Quadrature Encoder Peripheral
+	  driver.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called intel-qep.
+
+config INTERRUPT_CNT
+	tristate "Interrupt counter driver"
+	depends on GPIOLIB
+	help
+	  Select this option to enable interrupt counter driver. Any interrupt
+	  source can be used by this driver as the event source.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called interrupt-cnt.
+
+config MICROCHIP_TCB_CAPTURE
+	tristate "Microchip Timer Counter Capture driver"
+	depends on SOC_AT91SAM9 || SOC_SAM_V7 || COMPILE_TEST
+	depends on HAS_IOMEM && OF
+	select REGMAP_MMIO
+	help
+	  Select this option to enable the Microchip Timer Counter Block
+	  capture driver.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called microchip-tcb-capture.
+
+config RZ_MTU3_CNT
+	tristate "Renesas RZ/G2L MTU3a counter driver"
+	depends on RZ_MTU3
+	help
+	  Enable support for MTU3a counter driver found on Renesas RZ/G2L alike
+	  SoCs. This IP supports both 16-bit and 32-bit phase counting mode
+	  support.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called rz-mtu3-cnt.
+
+config STM32_LPTIMER_CNT
+	tristate "STM32 LP Timer encoder counter driver"
+	depends on MFD_STM32_LPTIMER || COMPILE_TEST
+	help
+	  Select this option to enable STM32 Low-Power Timer quadrature encoder
+	  and counter driver.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called stm32-lptimer-cnt.
+
+config STM32_TIMER_CNT
+	tristate "STM32 Timer encoder counter driver"
+	depends on MFD_STM32_TIMERS || COMPILE_TEST
+	help
+	  Select this option to enable STM32 Timer quadrature encoder
+	  and counter driver.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called stm32-timer-cnt.
+
+config TI_ECAP_CAPTURE
+	tristate "TI eCAP capture driver"
+	depends on ARCH_OMAP2PLUS || ARCH_DAVINCI_DA8XX || ARCH_KEYSTONE || ARCH_K3 || COMPILE_TEST
+	depends on HAS_IOMEM
+	select REGMAP_MMIO
+	help
+	  Select this option to enable the Texas Instruments Enhanced Capture
+	  (eCAP) driver in input mode.
+
+	  It can be used to timestamp events (falling/rising edges) detected
+	  on ECAP input signal.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called ti-ecap-capture.
+
+config TI_EQEP
+	tristate "TI eQEP counter driver"
+	depends on SOC_AM33XX || ARCH_K3 || COMPILE_TEST
+	select REGMAP_MMIO
+	help
+	  Select this option to enable the Texas Instruments Enhanced Quadrature
+	  Encoder Pulse (eQEP) counter driver.
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called ti-eqep.
+
+endif # COUNTER