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, 92 insertions, 0 deletions

diff --git a/include/uapi/mtd/inftl-user.h b/include/uapi/mtd/inftl-user.h
new file mode 100644
index 000000000..8d5044e32
--- /dev/null
+++ b/include/uapi/mtd/inftl-user.h
@@ -0,0 +1,92 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Parts of INFTL headers shared with userspace
+ *
+ */
+
+#ifndef __MTD_INFTL_USER_H__
+#define __MTD_INFTL_USER_H__
+
+#include <linux/types.h>
+
+#define	OSAK_VERSION	0x5120
+#define	PERCENTUSED	98
+
+#define	SECTORSIZE	512
+
+/* Block Control Information */
+
+struct inftl_bci {
+	__u8 ECCsig[6];
+	__u8 Status;
+	__u8 Status1;
+} __attribute__((packed));
+
+struct inftl_unithead1 {
+	__u16 virtualUnitNo;
+	__u16 prevUnitNo;
+	__u8 ANAC;
+	__u8 NACs;
+	__u8 parityPerField;
+	__u8 discarded;
+} __attribute__((packed));
+
+struct inftl_unithead2 {
+	__u8 parityPerField;
+	__u8 ANAC;
+	__u16 prevUnitNo;
+	__u16 virtualUnitNo;
+	__u8 NACs;
+	__u8 discarded;
+} __attribute__((packed));
+
+struct inftl_unittail {
+	__u8 Reserved[4];
+	__u16 EraseMark;
+	__u16 EraseMark1;
+} __attribute__((packed));
+
+union inftl_uci {
+	struct inftl_unithead1 a;
+	struct inftl_unithead2 b;
+	struct inftl_unittail c;
+};
+
+struct inftl_oob {
+	struct inftl_bci b;
+	union inftl_uci u;
+};
+
+
+/* INFTL Media Header */
+
+struct INFTLPartition {
+	__u32 virtualUnits;
+	__u32 firstUnit;
+	__u32 lastUnit;
+	__u32 flags;
+	__u32 spareUnits;
+	__u32 Reserved0;
+	__u32 Reserved1;
+} __attribute__((packed));
+
+struct INFTLMediaHeader {
+	char bootRecordID[8];
+	__u32 NoOfBootImageBlocks;
+	__u32 NoOfBinaryPartitions;
+	__u32 NoOfBDTLPartitions;
+	__u32 BlockMultiplierBits;
+	__u32 FormatFlags;
+	__u32 OsakVersion;
+	__u32 PercentUsed;
+	struct INFTLPartition Partitions[4];
+} __attribute__((packed));
+
+/* Partition flag types */
+#define	INFTL_BINARY	0x20000000
+#define	INFTL_BDTL	0x40000000
+#define	INFTL_LAST	0x80000000
+
+#endif /* __MTD_INFTL_USER_H__ */
+
+