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, 139 insertions, 0 deletions

diff --git a/include/video/uvesafb.h b/include/video/uvesafb.h
new file mode 100644
index 000000000..47d96e75e
--- /dev/null
+++ b/include/video/uvesafb.h
@@ -0,0 +1,139 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _UVESAFB_H
+#define _UVESAFB_H
+
+#include <uapi/video/uvesafb.h>
+
+
+/* VBE CRTC Info Block */
+struct vbe_crtc_ib {
+	u16 horiz_total;
+	u16 horiz_start;
+	u16 horiz_end;
+	u16 vert_total;
+	u16 vert_start;
+	u16 vert_end;
+	u8  flags;
+	u32 pixel_clock;
+	u16 refresh_rate;
+	u8  reserved[40];
+} __attribute__ ((packed));
+
+#define VBE_MODE_VGACOMPAT	0x20
+#define VBE_MODE_COLOR		0x08
+#define VBE_MODE_SUPPORTEDHW	0x01
+#define VBE_MODE_GRAPHICS	0x10
+#define VBE_MODE_LFB		0x80
+
+#define VBE_MODE_MASK		(VBE_MODE_COLOR | VBE_MODE_SUPPORTEDHW | \
+				VBE_MODE_GRAPHICS | VBE_MODE_LFB)
+
+/* VBE Mode Info Block */
+struct vbe_mode_ib {
+	/* for all VBE revisions */
+	u16 mode_attr;
+	u8  winA_attr;
+	u8  winB_attr;
+	u16 win_granularity;
+	u16 win_size;
+	u16 winA_seg;
+	u16 winB_seg;
+	u32 win_func_ptr;
+	u16 bytes_per_scan_line;
+
+	/* for VBE 1.2+ */
+	u16 x_res;
+	u16 y_res;
+	u8  x_char_size;
+	u8  y_char_size;
+	u8  planes;
+	u8  bits_per_pixel;
+	u8  banks;
+	u8  memory_model;
+	u8  bank_size;
+	u8  image_pages;
+	u8  reserved1;
+
+	/* Direct color fields for direct/6 and YUV/7 memory models. */
+	/* Offsets are bit positions of lsb in the mask. */
+	u8  red_len;
+	u8  red_off;
+	u8  green_len;
+	u8  green_off;
+	u8  blue_len;
+	u8  blue_off;
+	u8  rsvd_len;
+	u8  rsvd_off;
+	u8  direct_color_info;	/* direct color mode attributes */
+
+	/* for VBE 2.0+ */
+	u32 phys_base_ptr;
+	u8  reserved2[6];
+
+	/* for VBE 3.0+ */
+	u16 lin_bytes_per_scan_line;
+	u8  bnk_image_pages;
+	u8  lin_image_pages;
+	u8  lin_red_len;
+	u8  lin_red_off;
+	u8  lin_green_len;
+	u8  lin_green_off;
+	u8  lin_blue_len;
+	u8  lin_blue_off;
+	u8  lin_rsvd_len;
+	u8  lin_rsvd_off;
+	u32 max_pixel_clock;
+	u16 mode_id;
+	u8  depth;
+} __attribute__ ((packed));
+
+#define UVESAFB_DEFAULT_MODE "640x480-16"
+
+/* How long to wait for a reply from userspace [ms] */
+#define UVESAFB_TIMEOUT 5000
+
+/* Max number of concurrent tasks */
+#define UVESAFB_TASKS_MAX 16
+
+#define dac_reg	(0x3c8)
+#define dac_val	(0x3c9)
+
+struct uvesafb_pal_entry {
+	u_char blue, green, red, pad;
+} __attribute__ ((packed));
+
+struct uvesafb_ktask {
+	struct uvesafb_task t;
+	void *buf;
+	struct completion *done;
+	u32 ack;
+};
+
+#define UVESAFB_EXACT_RES	1
+#define UVESAFB_EXACT_DEPTH	2
+
+struct uvesafb_par {
+	struct vbe_ib vbe_ib;		/* VBE Info Block */
+	struct vbe_mode_ib *vbe_modes;	/* list of supported VBE modes */
+	int vbe_modes_cnt;
+
+	u8 nocrtc;
+	u8 ypan;			/* 0 - nothing, 1 - ypan, 2 - ywrap */
+	u8 pmi_setpal;			/* PMI for palette changes */
+	u16 *pmi_base;			/* protected mode interface location */
+	void *pmi_start;
+	void *pmi_pal;
+	u8 *vbe_state_orig;		/*
+					 * original hardware state, before the
+					 * driver was loaded
+					 */
+	u8 *vbe_state_saved;		/* state saved by fb_save_state */
+	int vbe_state_size;
+	atomic_t ref_count;
+
+	int mode_idx;
+	struct vbe_crtc_ib crtc;
+	int mtrr_handle;
+};
+
+#endif /* _UVESAFB_H */