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, 36 insertions, 0 deletions

diff --git a/drivers/ipack/devices/ipoctal.h b/drivers/ipack/devices/ipoctal.h
new file mode 100644
index 000000000..773dc41bd
--- /dev/null
+++ b/drivers/ipack/devices/ipoctal.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * driver for the IPOCTAL boards
+ *
+ * Copyright (C) 2009-2012 CERN (www.cern.ch)
+ * Author: Nicolas Serafini, EIC2 SA
+ * Author: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
+ */
+
+#ifndef _IPOCTAL_H_
+#define _IPOCTAL_H_
+
+#define NR_CHANNELS		8
+#define IPOCTAL_MAX_BOARDS	16
+#define MAX_DEVICES		(NR_CHANNELS * IPOCTAL_MAX_BOARDS)
+
+/**
+ * struct ipoctal_stats -- Stats since last reset
+ *
+ * @tx: Number of transmitted bytes
+ * @rx: Number of received bytes
+ * @overrun: Number of overrun errors
+ * @parity_err: Number of parity errors
+ * @framing_err: Number of framing errors
+ * @rcv_break: Number of break received
+ */
+struct ipoctal_stats {
+	unsigned long tx;
+	unsigned long rx;
+	unsigned long overrun_err;
+	unsigned long parity_err;
+	unsigned long framing_err;
+	unsigned long rcv_break;
+};
+
+#endif /* _IPOCTAL_H_ */