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, 72 insertions, 0 deletions

diff --git a/drivers/clocksource/timer-of.h b/drivers/clocksource/timer-of.h
new file mode 100644
index 000000000..74a632b85
--- /dev/null
+++ b/drivers/clocksource/timer-of.h
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __TIMER_OF_H__
+#define __TIMER_OF_H__
+
+#include <linux/clockchips.h>
+
+#define TIMER_OF_BASE	0x1
+#define TIMER_OF_CLOCK	0x2
+#define TIMER_OF_IRQ	0x4
+
+struct of_timer_irq {
+	int irq;
+	int index;
+	const char *name;
+	unsigned long flags;
+	irq_handler_t handler;
+};
+
+struct of_timer_base {
+	void __iomem *base;
+	const char *name;
+	int index;
+};
+
+struct of_timer_clk {
+	struct clk *clk;
+	const char *name;
+	int index;
+	unsigned long rate;
+	unsigned long period;
+};
+
+struct timer_of {
+	unsigned int flags;
+	struct device_node *np;
+	struct clock_event_device clkevt;
+	struct of_timer_base of_base;
+	struct of_timer_irq  of_irq;
+	struct of_timer_clk  of_clk;
+	void *private_data;
+};
+
+static inline struct timer_of *to_timer_of(struct clock_event_device *clkevt)
+{
+	return container_of(clkevt, struct timer_of, clkevt);
+}
+
+static inline void __iomem *timer_of_base(struct timer_of *to)
+{
+	return to->of_base.base;
+}
+
+static inline int timer_of_irq(struct timer_of *to)
+{
+	return to->of_irq.irq;
+}
+
+static inline unsigned long timer_of_rate(struct timer_of *to)
+{
+	return to->of_clk.rate;
+}
+
+static inline unsigned long timer_of_period(struct timer_of *to)
+{
+	return to->of_clk.period;
+}
+
+int timer_of_init(struct device_node *np, struct timer_of *to);
+
+void timer_of_cleanup(struct timer_of *to);
+
+#endif