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, 54 insertions, 0 deletions

diff --git a/include/uapi/sound/scarlett2.h b/include/uapi/sound/scarlett2.h
new file mode 100644
index 000000000..91467ab0e
--- /dev/null
+++ b/include/uapi/sound/scarlett2.h
@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ *   Focusrite Scarlett 2 Protocol Driver for ALSA
+ *   (including Scarlett 2nd Gen, 3rd Gen, 4th Gen, Clarett USB, and
+ *   Clarett+ series products)
+ *
+ *   Copyright (c) 2023 by Geoffrey D. Bennett <g at b4.vu>
+ */
+#ifndef __UAPI_SOUND_SCARLETT2_H
+#define __UAPI_SOUND_SCARLETT2_H
+
+#include <linux/types.h>
+#include <linux/ioctl.h>
+
+#define SCARLETT2_HWDEP_MAJOR 1
+#define SCARLETT2_HWDEP_MINOR 0
+#define SCARLETT2_HWDEP_SUBMINOR 0
+
+#define SCARLETT2_HWDEP_VERSION \
+	((SCARLETT2_HWDEP_MAJOR << 16) | \
+	 (SCARLETT2_HWDEP_MINOR << 8) | \
+	  SCARLETT2_HWDEP_SUBMINOR)
+
+#define SCARLETT2_HWDEP_VERSION_MAJOR(v) (((v) >> 16) & 0xFF)
+#define SCARLETT2_HWDEP_VERSION_MINOR(v) (((v) >> 8) & 0xFF)
+#define SCARLETT2_HWDEP_VERSION_SUBMINOR(v) ((v) & 0xFF)
+
+/* Get protocol version */
+#define SCARLETT2_IOCTL_PVERSION _IOR('S', 0x60, int)
+
+/* Reboot */
+#define SCARLETT2_IOCTL_REBOOT _IO('S', 0x61)
+
+/* Select flash segment */
+#define SCARLETT2_SEGMENT_ID_SETTINGS 0
+#define SCARLETT2_SEGMENT_ID_FIRMWARE 1
+#define SCARLETT2_SEGMENT_ID_COUNT 2
+
+#define SCARLETT2_IOCTL_SELECT_FLASH_SEGMENT _IOW('S', 0x62, int)
+
+/* Erase selected flash segment */
+#define SCARLETT2_IOCTL_ERASE_FLASH_SEGMENT _IO('S', 0x63)
+
+/* Get selected flash segment erase progress
+ * 1 through to num_blocks, or 255 for complete
+ */
+struct scarlett2_flash_segment_erase_progress {
+	unsigned char progress;
+	unsigned char num_blocks;
+};
+#define SCARLETT2_IOCTL_GET_ERASE_PROGRESS \
+	_IOR('S', 0x64, struct scarlett2_flash_segment_erase_progress)
+
+#endif /* __UAPI_SOUND_SCARLETT2_H */