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, 63 insertions, 0 deletions

diff --git a/include/video/sa1100fb.h b/include/video/sa1100fb.h
new file mode 100644
index 000000000..4ab409653
--- /dev/null
+++ b/include/video/sa1100fb.h
@@ -0,0 +1,63 @@
+/*
+ * StrongARM 1100 LCD Controller Frame Buffer Device
+ *
+ * Copyright (C) 1999 Eric A. Thomas
+ *  Based on acornfb.c Copyright (C) Russell King.
+ *  
+ * 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 _VIDEO_SA1100FB_H
+#define _VIDEO_SA1100FB_H
+
+#include <linux/fb.h>
+#include <linux/types.h>
+
+#define RGB_4	0
+#define RGB_8	1
+#define RGB_16	2
+#define NR_RGB	3
+
+/* These are the bitfields for each display depth that we support. */
+struct sa1100fb_rgb {
+	struct fb_bitfield	red;
+	struct fb_bitfield	green;
+	struct fb_bitfield	blue;
+	struct fb_bitfield	transp;
+};
+
+/* This structure describes the machine which we are running on. */
+struct sa1100fb_mach_info {
+	u_long		pixclock;
+
+	u_short		xres;
+	u_short		yres;
+
+	u_char		bpp;
+	u_char		hsync_len;
+	u_char		left_margin;
+	u_char		right_margin;
+
+	u_char		vsync_len;
+	u_char		upper_margin;
+	u_char		lower_margin;
+	u_char		sync;
+
+	u_int		cmap_greyscale:1,
+			cmap_inverse:1,
+			cmap_static:1,
+			unused:29;
+
+	u_int		lccr0;
+	u_int		lccr3;
+
+	/* Overrides for the default RGB maps */
+	const struct sa1100fb_rgb *rgb[NR_RGB];
+
+	void (*backlight_power)(int);
+	void (*lcd_power)(int);
+	void (*set_visual)(u32);
+};
+
+#endif