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, 58 insertions, 0 deletions

diff --git a/include/video/pmagb-b-fb.h b/include/video/pmagb-b-fb.h
new file mode 100644
index 000000000..7539b9087
--- /dev/null
+++ b/include/video/pmagb-b-fb.h
@@ -0,0 +1,58 @@
+/*
+ *	linux/include/video/pmagb-b-fb.h
+ *
+ *	TURBOchannel PMAGB-B Smart Frame Buffer (SFB) card support,
+ *	Copyright (C) 1999, 2000, 2001 by
+ *	Michael Engel <engel@unix-ag.org> and
+ *	Karsten Merker <merker@linuxtag.org>
+ *	Copyright (c) 2005  Maciej W. Rozycki
+ *
+ *	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.
+ */
+
+/* IOmem resource offsets.  */
+#define PMAGB_B_ROM		0x000000	/* REX option ROM */
+#define PMAGB_B_SFB		0x100000	/* SFB ASIC */
+#define PMAGB_B_GP0		0x140000	/* general purpose output 0 */
+#define PMAGB_B_GP1		0x180000	/* general purpose output 1 */
+#define PMAGB_B_BT459		0x1c0000	/* Bt459 RAMDAC */
+#define PMAGB_B_FBMEM		0x200000	/* frame buffer */
+#define PMAGB_B_SIZE		0x400000	/* address space size */
+
+/* IOmem register offsets.  */
+#define SFB_REG_VID_HOR		0x64		/* video horizontal setup */
+#define SFB_REG_VID_VER		0x68		/* video vertical setup */
+#define SFB_REG_VID_BASE	0x6c		/* video base address */
+#define SFB_REG_TCCLK_COUNT	0x78		/* TURBOchannel clock count */
+#define SFB_REG_VIDCLK_COUNT	0x7c		/* video clock count */
+
+/* Video horizontal setup register constants.  All bits are r/w.  */
+#define SFB_VID_HOR_BP_SHIFT	0x15		/* back porch */
+#define SFB_VID_HOR_BP_MASK	0x7f
+#define SFB_VID_HOR_SYN_SHIFT	0x0e		/* sync pulse */
+#define SFB_VID_HOR_SYN_MASK	0x7f
+#define SFB_VID_HOR_FP_SHIFT	0x09		/* front porch */
+#define SFB_VID_HOR_FP_MASK	0x1f
+#define SFB_VID_HOR_PIX_SHIFT	0x00		/* active video */
+#define SFB_VID_HOR_PIX_MASK	0x1ff
+
+/* Video vertical setup register constants.  All bits are r/w.  */
+#define SFB_VID_VER_BP_SHIFT	0x16		/* back porch */
+#define SFB_VID_VER_BP_MASK	0x3f
+#define SFB_VID_VER_SYN_SHIFT	0x10		/* sync pulse */
+#define SFB_VID_VER_SYN_MASK	0x3f
+#define SFB_VID_VER_FP_SHIFT	0x0b		/* front porch */
+#define SFB_VID_VER_FP_MASK	0x1f
+#define SFB_VID_VER_SL_SHIFT	0x00		/* active scan lines */
+#define SFB_VID_VER_SL_MASK	0x7ff
+
+/* Video base address register constants.  All bits are r/w.  */
+#define SFB_VID_BASE_MASK	0x1ff		/* video base row address */
+
+/* Bt459 register offsets, byte-wide registers.  */
+#define BT459_ADDR_LO		0x0		/* address low */
+#define BT459_ADDR_HI		0x4		/* address high */
+#define BT459_DATA		0x8		/* data window register */
+#define BT459_CMAP		0xc		/* color map window register */