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, 56 insertions, 0 deletions

diff --git a/include/video/omapvrfb.h b/include/video/omapvrfb.h
new file mode 100644
index 000000000..9741e77f1
--- /dev/null
+++ b/include/video/omapvrfb.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * VRFB Rotation Engine
+ *
+ * Copyright (C) 2009 Nokia Corporation
+ * Author: Tomi Valkeinen <tomi.valkeinen@nokia.com>
+ */
+
+#ifndef __OMAP_VRFB_H__
+#define __OMAP_VRFB_H__
+
+#define OMAP_VRFB_LINE_LEN 2048
+
+struct vrfb {
+	u8 context;
+	void __iomem *vaddr[4];
+	unsigned long paddr[4];
+	u16 xres;
+	u16 yres;
+	u16 xoffset;
+	u16 yoffset;
+	u8 bytespp;
+	bool yuv_mode;
+};
+
+#ifdef CONFIG_OMAP2_VRFB
+extern bool omap_vrfb_supported(void);
+extern int omap_vrfb_request_ctx(struct vrfb *vrfb);
+extern void omap_vrfb_release_ctx(struct vrfb *vrfb);
+extern void omap_vrfb_adjust_size(u16 *width, u16 *height,
+		u8 bytespp);
+extern u32 omap_vrfb_min_phys_size(u16 width, u16 height, u8 bytespp);
+extern u16 omap_vrfb_max_height(u32 phys_size, u16 width, u8 bytespp);
+extern void omap_vrfb_setup(struct vrfb *vrfb, unsigned long paddr,
+		u16 width, u16 height,
+		unsigned bytespp, bool yuv_mode);
+extern int omap_vrfb_map_angle(struct vrfb *vrfb, u16 height, u8 rot);
+extern void omap_vrfb_restore_context(void);
+
+#else
+static inline bool omap_vrfb_supported(void) { return false; }
+static inline int omap_vrfb_request_ctx(struct vrfb *vrfb) { return 0; }
+static inline void omap_vrfb_release_ctx(struct vrfb *vrfb) {}
+static inline void omap_vrfb_adjust_size(u16 *width, u16 *height,
+		u8 bytespp) {}
+static inline u32 omap_vrfb_min_phys_size(u16 width, u16 height, u8 bytespp)
+		{ return 0; }
+static inline u16 omap_vrfb_max_height(u32 phys_size, u16 width, u8 bytespp)
+		{ return 0; }
+static inline void omap_vrfb_setup(struct vrfb *vrfb, unsigned long paddr,
+		u16 width, u16 height, unsigned bytespp, bool yuv_mode) {}
+static inline int omap_vrfb_map_angle(struct vrfb *vrfb, u16 height, u8 rot)
+		{ return 0; }
+static inline void omap_vrfb_restore_context(void) {}
+#endif
+#endif /* __VRFB_H */