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, 78 insertions, 0 deletions

diff --git a/fs/udf/udfend.h b/fs/udf/udfend.h
new file mode 100644
index 000000000..a4363ac2c
--- /dev/null
+++ b/fs/udf/udfend.h
@@ -0,0 +1,78 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UDF_ENDIAN_H
+#define __UDF_ENDIAN_H
+
+#include <asm/byteorder.h>
+#include <linux/string.h>
+
+static inline struct kernel_lb_addr lelb_to_cpu(struct lb_addr in)
+{
+	struct kernel_lb_addr out;
+
+	out.logicalBlockNum = le32_to_cpu(in.logicalBlockNum);
+	out.partitionReferenceNum = le16_to_cpu(in.partitionReferenceNum);
+
+	return out;
+}
+
+static inline struct lb_addr cpu_to_lelb(struct kernel_lb_addr in)
+{
+	struct lb_addr out;
+
+	out.logicalBlockNum = cpu_to_le32(in.logicalBlockNum);
+	out.partitionReferenceNum = cpu_to_le16(in.partitionReferenceNum);
+
+	return out;
+}
+
+static inline struct short_ad lesa_to_cpu(struct short_ad in)
+{
+	struct short_ad out;
+
+	out.extLength = le32_to_cpu(in.extLength);
+	out.extPosition = le32_to_cpu(in.extPosition);
+
+	return out;
+}
+
+static inline struct short_ad cpu_to_lesa(struct short_ad in)
+{
+	struct short_ad out;
+
+	out.extLength = cpu_to_le32(in.extLength);
+	out.extPosition = cpu_to_le32(in.extPosition);
+
+	return out;
+}
+
+static inline struct kernel_long_ad lela_to_cpu(struct long_ad in)
+{
+	struct kernel_long_ad out;
+
+	out.extLength = le32_to_cpu(in.extLength);
+	out.extLocation = lelb_to_cpu(in.extLocation);
+
+	return out;
+}
+
+static inline struct long_ad cpu_to_lela(struct kernel_long_ad in)
+{
+	struct long_ad out;
+
+	out.extLength = cpu_to_le32(in.extLength);
+	out.extLocation = cpu_to_lelb(in.extLocation);
+
+	return out;
+}
+
+static inline struct kernel_extent_ad leea_to_cpu(struct extent_ad in)
+{
+	struct kernel_extent_ad out;
+
+	out.extLength = le32_to_cpu(in.extLength);
+	out.extLocation = le32_to_cpu(in.extLocation);
+
+	return out;
+}
+
+#endif /* __UDF_ENDIAN_H */