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, 34 insertions, 0 deletions

diff --git a/drivers/gpib/common/ibsys.h b/drivers/gpib/common/ibsys.h
new file mode 100644
index 000000000..e5a148f51
--- /dev/null
+++ b/drivers/gpib/common/ibsys.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include "gpibP.h"
+
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/errno.h>
+#include <linux/major.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/mm.h>
+#include <linux/timer.h>
+
+#include <linux/io.h>
+#include <linux/uaccess.h>
+#include <asm/irq.h>
+#include <asm/dma.h>
+
+#define MAX_GPIB_PRIMARY_ADDRESS 30
+#define MAX_GPIB_SECONDARY_ADDRESS 31
+
+int gpib_allocate_board(struct gpib_board *board);
+void gpib_deallocate_board(struct gpib_board *board);
+
+unsigned int num_status_bytes(const struct gpib_status_queue *dev);
+int push_status_byte(struct gpib_board *board, struct gpib_status_queue *device,
+		     u8 poll_byte);
+int pop_status_byte(struct gpib_board *board, struct gpib_status_queue *device,
+		    u8 *poll_byte);
+struct gpib_status_queue *get_gpib_status_queue(struct gpib_board *board,
+						unsigned int pad, int sad);
+int get_serial_poll_byte(struct gpib_board *board, unsigned int pad, int sad,
+			 unsigned int usec_timeout, u8 *poll_byte);
+int autopoll_all_devices(struct gpib_board *board);