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, 73 insertions, 0 deletions

diff --git a/drivers/scsi/a3000.h b/drivers/scsi/a3000.h
new file mode 100644
index 000000000..5cb3e7535
--- /dev/null
+++ b/drivers/scsi/a3000.h
@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef A3000_H
+#define A3000_H
+
+/* $Id: a3000.h,v 1.4 1997/01/19 23:07:10 davem Exp $
+ *
+ * Header file for the Amiga 3000 built-in SCSI controller for Linux
+ *
+ * Written and (C) 1993, Hamish Macdonald, see a3000.c for more info
+ *
+ */
+
+#include <linux/types.h>
+
+#ifndef CMD_PER_LUN
+#define CMD_PER_LUN		2
+#endif
+
+#ifndef CAN_QUEUE
+#define CAN_QUEUE		16
+#endif
+
+/*
+ * if the transfer address ANDed with this results in a non-zero
+ * result, then we can't use DMA.
+ */
+#define A3000_XFER_MASK		(0x00000003)
+
+struct a3000_scsiregs {
+		 unsigned char	pad1[2];
+	volatile unsigned short	DAWR;
+	volatile unsigned int	WTC;
+		 unsigned char	pad2[2];
+	volatile unsigned short	CNTR;
+	volatile unsigned long	ACR;
+		 unsigned char	pad3[2];
+	volatile unsigned short	ST_DMA;
+		 unsigned char	pad4[2];
+	volatile unsigned short	FLUSH;
+		 unsigned char	pad5[2];
+	volatile unsigned short	CINT;
+		 unsigned char	pad6[2];
+	volatile unsigned short	ISTR;
+		 unsigned char	pad7[30];
+	volatile unsigned short	SP_DMA;
+		 unsigned char	pad8;
+	volatile unsigned char	SASR;
+		 unsigned char	pad9;
+	volatile unsigned char	SCMD;
+};
+
+#define DAWR_A3000		(3)
+
+/* CNTR bits. */
+#define CNTR_TCEN		(1<<5)
+#define CNTR_PREST		(1<<4)
+#define CNTR_PDMD		(1<<3)
+#define CNTR_INTEN		(1<<2)
+#define CNTR_DDIR		(1<<1)
+#define CNTR_IO_DX		(1<<0)
+
+/* ISTR bits. */
+#define ISTR_INTX		(1<<8)
+#define ISTR_INT_F		(1<<7)
+#define ISTR_INTS		(1<<6)
+#define ISTR_E_INT		(1<<5)
+#define ISTR_INT_P		(1<<4)
+#define ISTR_UE_INT		(1<<3)
+#define ISTR_OE_INT		(1<<2)
+#define ISTR_FF_FLG		(1<<1)
+#define ISTR_FE_FLG		(1<<0)
+
+#endif /* A3000_H */