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, 82 insertions, 0 deletions

diff --git a/drivers/edac/mce_amd.h b/drivers/edac/mce_amd.h
new file mode 100644
index 000000000..4811b18d9
--- /dev/null
+++ b/drivers/edac/mce_amd.h
@@ -0,0 +1,82 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _EDAC_MCE_AMD_H
+#define _EDAC_MCE_AMD_H
+
+#include <linux/notifier.h>
+
+#include <asm/mce.h>
+
+#define EC(x)				((x) & 0xffff)
+
+#define LOW_SYNDROME(x)			(((x) >> 15) & 0xff)
+#define HIGH_SYNDROME(x)		(((x) >> 24) & 0xff)
+
+#define TLB_ERROR(x)			(((x) & 0xFFF0) == 0x0010)
+#define MEM_ERROR(x)			(((x) & 0xFF00) == 0x0100)
+#define BUS_ERROR(x)			(((x) & 0xF800) == 0x0800)
+#define INT_ERROR(x)			(((x) & 0xF4FF) == 0x0400)
+
+#define TT(x)				(((x) >> 2) & 0x3)
+#define TT_MSG(x)			tt_msgs[TT(x)]
+#define II(x)				(((x) >> 2) & 0x3)
+#define II_MSG(x)			ii_msgs[II(x)]
+#define LL(x)				((x) & 0x3)
+#define LL_MSG(x)			ll_msgs[LL(x)]
+#define TO(x)				(((x) >> 8) & 0x1)
+#define TO_MSG(x)			to_msgs[TO(x)]
+#define PP(x)				(((x) >> 9) & 0x3)
+#define PP_MSG(x)			pp_msgs[PP(x)]
+#define UU(x)				(((x) >> 8) & 0x3)
+#define UU_MSG(x)			uu_msgs[UU(x)]
+
+#define R4(x)				(((x) >> 4) & 0xf)
+#define R4_MSG(x)			((R4(x) < 9) ?  rrrr_msgs[R4(x)] : "Wrong R4!")
+
+extern const char * const pp_msgs[];
+
+enum tt_ids {
+	TT_INSTR = 0,
+	TT_DATA,
+	TT_GEN,
+	TT_RESV,
+};
+
+enum ll_ids {
+	LL_RESV = 0,
+	LL_L1,
+	LL_L2,
+	LL_LG,
+};
+
+enum ii_ids {
+	II_MEM = 0,
+	II_RESV,
+	II_IO,
+	II_GEN,
+};
+
+enum rrrr_ids {
+	R4_GEN	= 0,
+	R4_RD,
+	R4_WR,
+	R4_DRD,
+	R4_DWR,
+	R4_IRD,
+	R4_PREF,
+	R4_EVICT,
+	R4_SNOOP,
+};
+
+/*
+ * per-family decoder ops
+ */
+struct amd_decoder_ops {
+	bool (*mc0_mce)(u16, u8);
+	bool (*mc1_mce)(u16, u8);
+	bool (*mc2_mce)(u16, u8);
+};
+
+void amd_register_ecc_decoder(void (*f)(int, struct mce *));
+void amd_unregister_ecc_decoder(void (*f)(int, struct mce *));
+
+#endif /* _EDAC_MCE_AMD_H */