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, 46 insertions, 0 deletions

diff --git a/drivers/tty/ipwireless/tty.h b/drivers/tty/ipwireless/tty.h
new file mode 100644
index 000000000..ec698d9f3
--- /dev/null
+++ b/drivers/tty/ipwireless/tty.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * IPWireless 3G PCMCIA Network Driver
+ *
+ * Original code
+ *   by Stephen Blackheath <stephen@blacksapphire.com>,
+ *      Ben Martel <benm@symmetric.co.nz>
+ *
+ * Copyrighted as follows:
+ *   Copyright (C) 2004 by Symmetric Systems Ltd (NZ)
+ *
+ * Various driver changes and rewrites, port to new kernels
+ *   Copyright (C) 2006-2007 Jiri Kosina
+ *
+ * Misc code cleanups and updates
+ *   Copyright (C) 2007 David Sterba
+ */
+
+#ifndef _IPWIRELESS_CS_TTY_H_
+#define _IPWIRELESS_CS_TTY_H_
+
+#include <linux/types.h>
+#include <linux/sched.h>
+
+#include <pcmcia/cistpl.h>
+#include <pcmcia/ds.h>
+
+struct ipw_tty;
+struct ipw_network;
+struct ipw_hardware;
+
+int ipwireless_tty_init(void);
+void ipwireless_tty_release(void);
+
+struct ipw_tty *ipwireless_tty_create(struct ipw_hardware *hw,
+				      struct ipw_network *net);
+void ipwireless_tty_free(struct ipw_tty *tty);
+void ipwireless_tty_received(struct ipw_tty *tty, unsigned char *data,
+			     unsigned int length);
+int ipwireless_tty_is_modem(struct ipw_tty *tty);
+void ipwireless_tty_notify_control_line_change(struct ipw_tty *tty,
+					       unsigned int channel_idx,
+					       unsigned int control_lines,
+					       unsigned int changed_mask);
+
+#endif