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/leds/leds.h b/drivers/leds/leds.h
new file mode 100644
index 000000000..bee46651e
--- /dev/null
+++ b/drivers/leds/leds.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * LED Core
+ *
+ * Copyright 2005 Openedhand Ltd.
+ *
+ * Author: Richard Purdie <rpurdie@openedhand.com>
+ */
+#ifndef __LEDS_H_INCLUDED
+#define __LEDS_H_INCLUDED
+
+#include <linux/rwsem.h>
+#include <linux/leds.h>
+
+static inline int led_get_brightness(struct led_classdev *led_cdev)
+{
+	return led_cdev->brightness;
+}
+
+void led_init_core(struct led_classdev *led_cdev);
+void led_stop_software_blink(struct led_classdev *led_cdev);
+void led_set_brightness_nopm(struct led_classdev *led_cdev, unsigned int value);
+void led_set_brightness_nosleep(struct led_classdev *led_cdev, unsigned int value);
+ssize_t led_trigger_read(struct file *filp, struct kobject *kobj,
+			const struct bin_attribute *attr, char *buf,
+			loff_t pos, size_t count);
+ssize_t led_trigger_write(struct file *filp, struct kobject *kobj,
+			const struct bin_attribute *bin_attr, char *buf,
+			loff_t pos, size_t count);
+
+extern struct rw_semaphore leds_list_lock;
+extern struct list_head leds_list;
+
+#endif	/* __LEDS_H_INCLUDED */