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, 56 insertions, 0 deletions

diff --git a/drivers/hwspinlock/Kconfig b/drivers/hwspinlock/Kconfig
new file mode 100644
index 000000000..d84e00084
--- /dev/null
+++ b/drivers/hwspinlock/Kconfig
@@ -0,0 +1,56 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Generic HWSPINLOCK framework
+#
+
+menuconfig HWSPINLOCK
+	bool "Hardware Spinlock drivers"
+
+if HWSPINLOCK
+
+config HWSPINLOCK_OMAP
+	tristate "OMAP Hardware Spinlock device"
+	depends on ARCH_OMAP4 || SOC_OMAP5 || SOC_DRA7XX || SOC_AM33XX || SOC_AM43XX || ARCH_K3 || COMPILE_TEST
+	help
+	  Say y here to support the OMAP Hardware Spinlock device (firstly
+	  introduced in OMAP4).
+
+	  If unsure, say N.
+
+config HWSPINLOCK_QCOM
+	tristate "Qualcomm Hardware Spinlock device"
+	depends on ARCH_QCOM || COMPILE_TEST
+	select MFD_SYSCON
+	help
+	  Say y here to support the Qualcomm Hardware Mutex functionality, which
+	  provides a synchronisation mechanism for the various processors on
+	  the SoC.
+
+	  If unsure, say N.
+
+config HWSPINLOCK_SPRD
+	tristate "SPRD Hardware Spinlock device"
+	depends on ARCH_SPRD || COMPILE_TEST
+	help
+	  Say y here to support the SPRD Hardware Spinlock device.
+
+	  If unsure, say N.
+
+config HWSPINLOCK_STM32
+	tristate "STM32 Hardware Spinlock device"
+	depends on MACH_STM32MP157 || COMPILE_TEST
+	help
+	  Say y here to support the STM32 Hardware Spinlock device.
+
+	  If unsure, say N.
+
+config HWSPINLOCK_SUN6I
+	tristate "SUN6I Hardware Spinlock device"
+	depends on ARCH_SUNXI || COMPILE_TEST
+	help
+	  Say y here to support the SUN6I Hardware Spinlock device which can be
+	  found in most of the sun6i compatible Allwinner SoCs.
+
+	  If unsure, say N.
+
+endif # HWSPINLOCK