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, 63 insertions, 0 deletions

diff --git a/lib/raid/Kconfig b/lib/raid/Kconfig
new file mode 100644
index 000000000..978cd6ba0
--- /dev/null
+++ b/lib/raid/Kconfig
@@ -0,0 +1,63 @@
+# SPDX-License-Identifier: GPL-2.0
+
+config XOR_BLOCKS
+	tristate
+
+# selected by architectures that provide an optimized XOR implementation
+config XOR_BLOCKS_ARCH
+	depends on XOR_BLOCKS
+	default y if ALPHA
+	default y if ARM
+	default y if ARM64
+	default y if CPU_HAS_LSX		# loongarch
+	default y if ALTIVEC			# powerpc
+	default y if RISCV_ISA_V
+	default y if SPARC
+	default y if S390
+	default y if X86_32
+	default y if X86_64
+	bool
+
+config XOR_KUNIT_TEST
+	tristate "KUnit tests for xor_gen" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	depends on XOR_BLOCKS
+	default KUNIT_ALL_TESTS
+	help
+	  Unit tests for the XOR library functions.
+
+	  This is intended to help people writing architecture-specific
+	  optimized versions.  If unsure, say N.
+
+config RAID6_PQ
+	tristate
+
+# selected by architectures that provide an optimized PQ implementation
+config RAID6_PQ_ARCH
+	depends on RAID6_PQ
+	default y if KERNEL_MODE_NEON		# arm32/arm64
+	default y if LOONGARCH
+	default y if ALTIVEC			# powerpc
+	default y if RISCV_ISA_V
+	default y if S390
+	default y if X86
+	bool
+
+config RAID6_PQ_KUNIT_TEST
+	tristate "KUnit tests for RAID6 PQ functions" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	depends on RAID6_PQ
+	default KUNIT_ALL_TESTS
+	help
+	  Unit tests for the RAID6 PQ library functions.
+
+	  This is intended to help people writing architecture-specific
+	  optimized versions.  If unsure, say N.
+
+config RAID6_PQ_BENCHMARK
+	bool "Automatically choose fastest RAID6 PQ functions"
+	depends on RAID6_PQ
+	default y
+	help
+	  Benchmark all available RAID6 PQ functions on init and choose the
+	  fastest one.