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, 57 insertions, 0 deletions

diff --git a/include/video/metronomefb.h b/include/video/metronomefb.h
new file mode 100644
index 000000000..9863f4b6d
--- /dev/null
+++ b/include/video/metronomefb.h
@@ -0,0 +1,57 @@
+/*
+ * metronomefb.h - definitions for the metronome framebuffer driver
+ *
+ * Copyright (C) 2008 by Jaya Kumar
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License. See the file COPYING in the main directory of this archive for
+ * more details.
+ *
+ */
+
+#ifndef _LINUX_METRONOMEFB_H_
+#define _LINUX_METRONOMEFB_H_
+
+/* command structure used by metronome controller */
+struct metromem_cmd {
+	u16 opcode;
+	u16 args[((64-2)/2)];
+	u16 csum;
+};
+
+/* struct used by metronome. board specific stuff comes from *board */
+struct metronomefb_par {
+	struct metromem_cmd *metromem_cmd;
+	unsigned char *metromem_wfm;
+	unsigned char *metromem_img;
+	u16 *metromem_img_csum;
+	u16 *csum_table;
+	dma_addr_t metromem_dma;
+	struct fb_info *info;
+	struct metronome_board *board;
+	wait_queue_head_t waitq;
+	u8 frame_count;
+	int extra_size;
+	int dt;
+};
+
+/* board specific routines and data */
+struct metronome_board {
+	struct module *owner; /* the platform device */
+	void (*set_rst)(struct metronomefb_par *, int);
+	void (*set_stdby)(struct metronomefb_par *, int);
+	void (*cleanup)(struct metronomefb_par *);
+	int (*met_wait_event)(struct metronomefb_par *);
+	int (*met_wait_event_intr)(struct metronomefb_par *);
+	int (*setup_irq)(struct fb_info *);
+	int (*setup_fb)(struct metronomefb_par *);
+	int (*setup_io)(struct metronomefb_par *);
+	int (*get_panel_type)(void);
+	unsigned char *metromem;
+	int fw;
+	int fh;
+	int wfm_size;
+	struct fb_info *host_fbinfo; /* the host LCD controller's fbi */
+};
+
+#endif