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, 38 insertions, 0 deletions

diff --git a/include/video/maxinefb.h b/include/video/maxinefb.h
new file mode 100644
index 000000000..6aeb4acca
--- /dev/null
+++ b/include/video/maxinefb.h
@@ -0,0 +1,38 @@
+/*
+ *      linux/drivers/video/maxinefb.h
+ *
+ *      DECstation 5000/xx onboard framebuffer support, Copyright (C) 1999 by
+ *      Michael Engel <engel@unix-ag.org> and Karsten Merker <merker@guug.de>
+ *      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.
+ */
+
+#include <asm/addrspace.h>
+
+/*
+ * IMS332 video controller register base address
+ */
+#define MAXINEFB_IMS332_ADDRESS		KSEG1ADDR(0x1c140000)
+
+/*
+ * Begin of DECstation 5000/xx onboard framebuffer memory, default resolution
+ * is 1024x768x8
+ */
+#define DS5000_xx_ONBOARD_FBMEM_START	KSEG1ADDR(0x0a000000)
+
+/*
+ *      The IMS 332 video controller used in the DECstation 5000/xx series
+ *      uses 32 bits wide registers; the following defines declare the
+ *      register numbers, to get the real offset, these have to be multiplied
+ *      by four.
+ */
+
+#define IMS332_REG_CURSOR_RAM           0x200	/* hardware cursor bitmap */
+
+/*
+ * The color palette entries have the form 0x00BBGGRR
+ */
+#define IMS332_REG_COLOR_PALETTE        0x100	/* color palette, 256 entries */
+#define IMS332_REG_CURSOR_COLOR_PALETTE	0x0a1	/* cursor color palette, */
+						/* 3 entries             */