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, 74 insertions, 0 deletions

diff --git a/include/video/broadsheetfb.h b/include/video/broadsheetfb.h
new file mode 100644
index 000000000..548d28f4e
--- /dev/null
+++ b/include/video/broadsheetfb.h
@@ -0,0 +1,74 @@
+/*
+ * broadsheetfb.h - definitions for the broadsheet 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_BROADSHEETFB_H_
+#define _LINUX_BROADSHEETFB_H_
+
+/* Broadsheet command defines */
+#define BS_CMD_INIT_SYS_RUN	0x06
+#define BS_CMD_INIT_DSPE_CFG	0x09
+#define BS_CMD_INIT_DSPE_TMG	0x0A
+#define BS_CMD_INIT_ROTMODE	0x0B
+#define BS_CMD_RD_REG		0x10
+#define BS_CMD_WR_REG		0x11
+#define BS_CMD_LD_IMG		0x20
+#define BS_CMD_LD_IMG_AREA	0x22
+#define BS_CMD_LD_IMG_END	0x23
+#define BS_CMD_WAIT_DSPE_TRG	0x28
+#define BS_CMD_WAIT_DSPE_FREND	0x29
+#define BS_CMD_RD_WFM_INFO	0x30
+#define BS_CMD_UPD_INIT		0x32
+#define BS_CMD_UPD_FULL		0x33
+#define BS_CMD_UPD_GDRV_CLR	0x37
+
+/* Broadsheet register interface defines */
+#define BS_REG_REV		0x00
+#define BS_REG_PRC		0x02
+
+/* Broadsheet pin interface specific defines */
+#define BS_CS	0x01
+#define BS_DC 	0x02
+#define BS_WR 	0x03
+
+/* Broadsheet IO interface specific defines */
+#define BS_MMIO_CMD	0x01
+#define BS_MMIO_DATA	0x02
+
+/* struct used by broadsheet. board specific stuff comes from *board */
+struct broadsheetfb_par {
+	struct fb_info *info;
+	struct broadsheet_board *board;
+	void (*write_reg)(struct broadsheetfb_par *, u16 reg, u16 val);
+	u16 (*read_reg)(struct broadsheetfb_par *, u16 reg);
+	wait_queue_head_t waitq;
+	int panel_index;
+	struct mutex io_lock;
+};
+
+/* board specific routines */
+struct broadsheet_board {
+	struct module *owner;
+	int (*init)(struct broadsheetfb_par *);
+	int (*wait_for_rdy)(struct broadsheetfb_par *);
+	void (*cleanup)(struct broadsheetfb_par *);
+	int (*get_panel_type)(void);
+	int (*setup_irq)(struct fb_info *);
+
+	/* Functions for boards that use GPIO */
+	void (*set_ctl)(struct broadsheetfb_par *, unsigned char, u8);
+	void (*set_hdb)(struct broadsheetfb_par *, u16);
+	u16 (*get_hdb)(struct broadsheetfb_par *);
+
+	/* Functions for boards that have specialized MMIO */
+	void (*mmio_write)(struct broadsheetfb_par *, int type, u16);
+	u16 (*mmio_read)(struct broadsheetfb_par *);
+};
+#endif