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, 53 insertions, 0 deletions

diff --git a/drivers/input/misc/ad714x.h b/drivers/input/misc/ad714x.h
new file mode 100644
index 000000000..dafa12325
--- /dev/null
+++ b/drivers/input/misc/ad714x.h
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * AD714X CapTouch Programmable Controller driver (bus interfaces)
+ *
+ * Copyright 2009-2011 Analog Devices Inc.
+ */
+
+#ifndef _AD714X_H_
+#define _AD714X_H_
+
+#include <linux/pm.h>
+#include <linux/types.h>
+
+#define STAGE_NUM              12
+
+struct device;
+struct ad714x_platform_data;
+struct ad714x_driver_data;
+struct ad714x_chip;
+
+typedef int (*ad714x_read_t)(struct ad714x_chip *, unsigned short, unsigned short *, size_t);
+typedef int (*ad714x_write_t)(struct ad714x_chip *, unsigned short, unsigned short);
+
+struct ad714x_chip {
+	unsigned short l_state;
+	unsigned short h_state;
+	unsigned short c_state;
+	unsigned short adc_reg[STAGE_NUM];
+	unsigned short amb_reg[STAGE_NUM];
+	unsigned short sensor_val[STAGE_NUM];
+
+	struct ad714x_platform_data *hw;
+	struct ad714x_driver_data *sw;
+
+	int irq;
+	struct device *dev;
+	ad714x_read_t read;
+	ad714x_write_t write;
+
+	struct mutex mutex;
+
+	unsigned product;
+	unsigned version;
+
+	__be16 xfer_buf[16] ____cacheline_aligned;
+
+};
+
+extern const struct dev_pm_ops ad714x_pm;
+struct ad714x_chip *ad714x_probe(struct device *dev, u16 bus_type, int irq,
+				 ad714x_read_t read, ad714x_write_t write);
+
+#endif