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, 37 insertions, 0 deletions

diff --git a/drivers/video/fbdev/atafb.h b/drivers/video/fbdev/atafb.h
new file mode 100644
index 000000000..2b2675980
--- /dev/null
+++ b/drivers/video/fbdev/atafb.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _VIDEO_ATAFB_H
+#define _VIDEO_ATAFB_H
+
+void atafb_mfb_copyarea(struct fb_info *info, u_long next_line, int sy, int sx, int dy,
+			int dx, int height, int width);
+void atafb_mfb_fillrect(struct fb_info *info, u_long next_line, u32 color,
+			int sy, int sx, int height, int width);
+void atafb_mfb_linefill(struct fb_info *info, u_long next_line,
+			int dy, int dx, u32 width,
+			const u8 *data, u32 bgcolor, u32 fgcolor);
+
+void atafb_iplan2p2_copyarea(struct fb_info *info, u_long next_line, int sy, int sx, int dy,
+			     int dx, int height, int width);
+void atafb_iplan2p2_fillrect(struct fb_info *info, u_long next_line, u32 color,
+			     int sy, int sx, int height, int width);
+void atafb_iplan2p2_linefill(struct fb_info *info, u_long next_line,
+			     int dy, int dx, u32 width,
+			     const u8 *data, u32 bgcolor, u32 fgcolor);
+
+void atafb_iplan2p4_copyarea(struct fb_info *info, u_long next_line, int sy, int sx, int dy,
+			     int dx, int height, int width);
+void atafb_iplan2p4_fillrect(struct fb_info *info, u_long next_line, u32 color,
+			     int sy, int sx, int height, int width);
+void atafb_iplan2p4_linefill(struct fb_info *info, u_long next_line,
+			     int dy, int dx, u32 width,
+			     const u8 *data, u32 bgcolor, u32 fgcolor);
+
+void atafb_iplan2p8_copyarea(struct fb_info *info, u_long next_line, int sy, int sx, int dy,
+			     int dx, int height, int width);
+void atafb_iplan2p8_fillrect(struct fb_info *info, u_long next_line, u32 color,
+			     int sy, int sx, int height, int width);
+void atafb_iplan2p8_linefill(struct fb_info *info, u_long next_line,
+			     int dy, int dx, u32 width,
+			     const u8 *data, u32 bgcolor, u32 fgcolor);
+
+#endif /* _VIDEO_ATAFB_H */