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, 343 insertions, 0 deletions

diff --git a/net/rfkill/input.c b/net/rfkill/input.c
new file mode 100644
index 000000000..f7cb24ce7
--- /dev/null
+++ b/net/rfkill/input.c
@@ -0,0 +1,343 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Input layer to RF Kill interface connector
+ *
+ * Copyright (c) 2007 Dmitry Torokhov
+ * Copyright 2009 Johannes Berg <johannes@sipsolutions.net>
+ *
+ * If you ever run into a situation in which you have a SW_ type rfkill
+ * input device, then you can revive code that was removed in the patch
+ * "rfkill-input: remove unused code".
+ */
+
+#include <linux/input.h>
+#include <linux/slab.h>
+#include <linux/moduleparam.h>
+#include <linux/workqueue.h>
+#include <linux/init.h>
+#include <linux/rfkill.h>
+#include <linux/sched.h>
+
+#include "rfkill.h"
+
+enum rfkill_input_master_mode {
+	RFKILL_INPUT_MASTER_UNLOCK = 0,
+	RFKILL_INPUT_MASTER_RESTORE = 1,
+	RFKILL_INPUT_MASTER_UNBLOCKALL = 2,
+	NUM_RFKILL_INPUT_MASTER_MODES
+};
+
+/* Delay (in ms) between consecutive switch ops */
+#define RFKILL_OPS_DELAY 200
+
+static enum rfkill_input_master_mode rfkill_master_switch_mode =
+					RFKILL_INPUT_MASTER_UNBLOCKALL;
+module_param_named(master_switch_mode, rfkill_master_switch_mode, uint, 0);
+MODULE_PARM_DESC(master_switch_mode,
+	"SW_RFKILL_ALL ON should: 0=do nothing (only unlock); 1=restore; 2=unblock all");
+
+static DEFINE_SPINLOCK(rfkill_op_lock);
+static bool rfkill_op_pending;
+static unsigned long rfkill_sw_pending[BITS_TO_LONGS(NUM_RFKILL_TYPES)];
+static unsigned long rfkill_sw_state[BITS_TO_LONGS(NUM_RFKILL_TYPES)];
+
+enum rfkill_sched_op {
+	RFKILL_GLOBAL_OP_EPO = 0,
+	RFKILL_GLOBAL_OP_RESTORE,
+	RFKILL_GLOBAL_OP_UNLOCK,
+	RFKILL_GLOBAL_OP_UNBLOCK,
+};
+
+static enum rfkill_sched_op rfkill_master_switch_op;
+static enum rfkill_sched_op rfkill_op;
+
+static void __rfkill_handle_global_op(enum rfkill_sched_op op)
+{
+	unsigned int i;
+
+	switch (op) {
+	case RFKILL_GLOBAL_OP_EPO:
+		rfkill_epo();
+		break;
+	case RFKILL_GLOBAL_OP_RESTORE:
+		rfkill_restore_states();
+		break;
+	case RFKILL_GLOBAL_OP_UNLOCK:
+		rfkill_remove_epo_lock();
+		break;
+	case RFKILL_GLOBAL_OP_UNBLOCK:
+		rfkill_remove_epo_lock();
+		for (i = 0; i < NUM_RFKILL_TYPES; i++)
+			rfkill_switch_all(i, false);
+		break;
+	default:
+		/* memory corruption or bug, fail safely */
+		rfkill_epo();
+		WARN(1, "Unknown requested operation %d! "
+			"rfkill Emergency Power Off activated\n",
+			op);
+	}
+}
+
+static void __rfkill_handle_normal_op(const enum rfkill_type type,
+				      const bool complement)
+{
+	bool blocked;
+
+	blocked = rfkill_get_global_sw_state(type);
+	if (complement)
+		blocked = !blocked;
+
+	rfkill_switch_all(type, blocked);
+}
+
+static void rfkill_op_handler(struct work_struct *work)
+{
+	unsigned int i;
+	bool c;
+
+	spin_lock_irq(&rfkill_op_lock);
+	do {
+		if (rfkill_op_pending) {
+			enum rfkill_sched_op op = rfkill_op;
+			rfkill_op_pending = false;
+			memset(rfkill_sw_pending, 0,
+				sizeof(rfkill_sw_pending));
+			spin_unlock_irq(&rfkill_op_lock);
+
+			__rfkill_handle_global_op(op);
+
+			spin_lock_irq(&rfkill_op_lock);
+
+			/*
+			 * handle global ops first -- during unlocked period
+			 * we might have gotten a new global op.
+			 */
+			if (rfkill_op_pending)
+				continue;
+		}
+
+		if (rfkill_is_epo_lock_active())
+			continue;
+
+		for (i = 0; i < NUM_RFKILL_TYPES; i++) {
+			if (__test_and_clear_bit(i, rfkill_sw_pending)) {
+				c = __test_and_clear_bit(i, rfkill_sw_state);
+				spin_unlock_irq(&rfkill_op_lock);
+
+				__rfkill_handle_normal_op(i, c);
+
+				spin_lock_irq(&rfkill_op_lock);
+			}
+		}
+	} while (rfkill_op_pending);
+	spin_unlock_irq(&rfkill_op_lock);
+}
+
+static DECLARE_DELAYED_WORK(rfkill_op_work, rfkill_op_handler);
+static unsigned long rfkill_last_scheduled;
+
+static unsigned long rfkill_ratelimit(const unsigned long last)
+{
+	const unsigned long delay = msecs_to_jiffies(RFKILL_OPS_DELAY);
+	return time_after(jiffies, last + delay) ? 0 : delay;
+}
+
+static void rfkill_schedule_ratelimited(void)
+{
+	if (schedule_delayed_work(&rfkill_op_work,
+				  rfkill_ratelimit(rfkill_last_scheduled)))
+		rfkill_last_scheduled = jiffies;
+}
+
+static void rfkill_schedule_global_op(enum rfkill_sched_op op)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&rfkill_op_lock, flags);
+	rfkill_op = op;
+	rfkill_op_pending = true;
+	if (op == RFKILL_GLOBAL_OP_EPO && !rfkill_is_epo_lock_active()) {
+		/* bypass the limiter for EPO */
+		mod_delayed_work(system_percpu_wq, &rfkill_op_work, 0);
+		rfkill_last_scheduled = jiffies;
+	} else
+		rfkill_schedule_ratelimited();
+	spin_unlock_irqrestore(&rfkill_op_lock, flags);
+}
+
+static void rfkill_schedule_toggle(enum rfkill_type type)
+{
+	unsigned long flags;
+
+	if (rfkill_is_epo_lock_active())
+		return;
+
+	spin_lock_irqsave(&rfkill_op_lock, flags);
+	if (!rfkill_op_pending) {
+		__set_bit(type, rfkill_sw_pending);
+		__change_bit(type, rfkill_sw_state);
+		rfkill_schedule_ratelimited();
+	}
+	spin_unlock_irqrestore(&rfkill_op_lock, flags);
+}
+
+static void rfkill_schedule_evsw_rfkillall(int state)
+{
+	if (state)
+		rfkill_schedule_global_op(rfkill_master_switch_op);
+	else
+		rfkill_schedule_global_op(RFKILL_GLOBAL_OP_EPO);
+}
+
+static void rfkill_event(struct input_handle *handle, unsigned int type,
+			unsigned int code, int data)
+{
+	if (type == EV_KEY && data == 1) {
+		switch (code) {
+		case KEY_WLAN:
+			rfkill_schedule_toggle(RFKILL_TYPE_WLAN);
+			break;
+		case KEY_BLUETOOTH:
+			rfkill_schedule_toggle(RFKILL_TYPE_BLUETOOTH);
+			break;
+		case KEY_UWB:
+			rfkill_schedule_toggle(RFKILL_TYPE_UWB);
+			break;
+		case KEY_WIMAX:
+			rfkill_schedule_toggle(RFKILL_TYPE_WIMAX);
+			break;
+		case KEY_RFKILL:
+			rfkill_schedule_toggle(RFKILL_TYPE_ALL);
+			break;
+		}
+	} else if (type == EV_SW && code == SW_RFKILL_ALL)
+		rfkill_schedule_evsw_rfkillall(data);
+}
+
+static int rfkill_connect(struct input_handler *handler, struct input_dev *dev,
+			  const struct input_device_id *id)
+{
+	struct input_handle *handle;
+	int error;
+
+	handle = kzalloc_obj(struct input_handle);
+	if (!handle)
+		return -ENOMEM;
+
+	handle->dev = dev;
+	handle->handler = handler;
+	handle->name = "rfkill";
+
+	/* causes rfkill_start() to be called */
+	error = input_register_handle(handle);
+	if (error)
+		goto err_free_handle;
+
+	error = input_open_device(handle);
+	if (error)
+		goto err_unregister_handle;
+
+	return 0;
+
+ err_unregister_handle:
+	input_unregister_handle(handle);
+ err_free_handle:
+	kfree(handle);
+	return error;
+}
+
+static void rfkill_start(struct input_handle *handle)
+{
+	/*
+	 * Take event_lock to guard against configuration changes, we
+	 * should be able to deal with concurrency with rfkill_event()
+	 * just fine (which event_lock will also avoid).
+	 */
+	spin_lock_irq(&handle->dev->event_lock);
+
+	if (test_bit(EV_SW, handle->dev->evbit) &&
+	    test_bit(SW_RFKILL_ALL, handle->dev->swbit))
+		rfkill_schedule_evsw_rfkillall(test_bit(SW_RFKILL_ALL,
+							handle->dev->sw));
+
+	spin_unlock_irq(&handle->dev->event_lock);
+}
+
+static void rfkill_disconnect(struct input_handle *handle)
+{
+	input_close_device(handle);
+	input_unregister_handle(handle);
+	kfree(handle);
+}
+
+static const struct input_device_id rfkill_ids[] = {
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_EVBIT | INPUT_DEVICE_ID_MATCH_KEYBIT,
+		.evbit = { BIT_MASK(EV_KEY) },
+		.keybit = { [BIT_WORD(KEY_WLAN)] = BIT_MASK(KEY_WLAN) },
+	},
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_EVBIT | INPUT_DEVICE_ID_MATCH_KEYBIT,
+		.evbit = { BIT_MASK(EV_KEY) },
+		.keybit = { [BIT_WORD(KEY_BLUETOOTH)] = BIT_MASK(KEY_BLUETOOTH) },
+	},
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_EVBIT | INPUT_DEVICE_ID_MATCH_KEYBIT,
+		.evbit = { BIT_MASK(EV_KEY) },
+		.keybit = { [BIT_WORD(KEY_UWB)] = BIT_MASK(KEY_UWB) },
+	},
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_EVBIT | INPUT_DEVICE_ID_MATCH_KEYBIT,
+		.evbit = { BIT_MASK(EV_KEY) },
+		.keybit = { [BIT_WORD(KEY_WIMAX)] = BIT_MASK(KEY_WIMAX) },
+	},
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_EVBIT | INPUT_DEVICE_ID_MATCH_KEYBIT,
+		.evbit = { BIT_MASK(EV_KEY) },
+		.keybit = { [BIT_WORD(KEY_RFKILL)] = BIT_MASK(KEY_RFKILL) },
+	},
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_EVBIT | INPUT_DEVICE_ID_MATCH_SWBIT,
+		.evbit = { BIT(EV_SW) },
+		.swbit = { [BIT_WORD(SW_RFKILL_ALL)] = BIT_MASK(SW_RFKILL_ALL) },
+	},
+	{ }
+};
+
+static struct input_handler rfkill_handler = {
+	.name =	"rfkill",
+	.event = rfkill_event,
+	.connect = rfkill_connect,
+	.start = rfkill_start,
+	.disconnect = rfkill_disconnect,
+	.id_table = rfkill_ids,
+};
+
+int __init rfkill_handler_init(void)
+{
+	switch (rfkill_master_switch_mode) {
+	case RFKILL_INPUT_MASTER_UNBLOCKALL:
+		rfkill_master_switch_op = RFKILL_GLOBAL_OP_UNBLOCK;
+		break;
+	case RFKILL_INPUT_MASTER_RESTORE:
+		rfkill_master_switch_op = RFKILL_GLOBAL_OP_RESTORE;
+		break;
+	case RFKILL_INPUT_MASTER_UNLOCK:
+		rfkill_master_switch_op = RFKILL_GLOBAL_OP_UNLOCK;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Avoid delay at first schedule */
+	rfkill_last_scheduled =
+			jiffies - msecs_to_jiffies(RFKILL_OPS_DELAY) - 1;
+	return input_register_handler(&rfkill_handler);
+}
+
+void __exit rfkill_handler_exit(void)
+{
+	input_unregister_handler(&rfkill_handler);
+	cancel_delayed_work_sync(&rfkill_op_work);
+}