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, 173 insertions, 0 deletions

diff --git a/net/mac802154/util.c b/net/mac802154/util.c
new file mode 100644
index 000000000..ebc9a8521
--- /dev/null
+++ b/net/mac802154/util.c
@@ -0,0 +1,173 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *
+ * Authors:
+ * Alexander Aring <aar@pengutronix.de>
+ *
+ * Based on: net/mac80211/util.c
+ */
+
+#include "ieee802154_i.h"
+#include "driver-ops.h"
+
+/* privid for wpan_phys to determine whether they belong to us or not */
+const void *const mac802154_wpan_phy_privid = &mac802154_wpan_phy_privid;
+
+/**
+ * ieee802154_wake_queue - wake ieee802154 queue
+ * @hw: main hardware object
+ *
+ * Tranceivers usually have either one transmit framebuffer or one framebuffer
+ * for both transmitting and receiving. Hence, the core currently only handles
+ * one frame at a time for each phy, which means we had to stop the queue to
+ * avoid new skb to come during the transmission. The queue then needs to be
+ * woken up after the operation.
+ */
+static void ieee802154_wake_queue(struct ieee802154_hw *hw)
+{
+	struct ieee802154_local *local = hw_to_local(hw);
+	struct ieee802154_sub_if_data *sdata;
+
+	rcu_read_lock();
+	clear_bit(WPAN_PHY_FLAG_STATE_QUEUE_STOPPED, &local->phy->flags);
+	list_for_each_entry_rcu(sdata, &local->interfaces, list) {
+		if (!sdata->dev)
+			continue;
+
+		netif_wake_queue(sdata->dev);
+	}
+	rcu_read_unlock();
+}
+
+/**
+ * ieee802154_stop_queue - stop ieee802154 queue
+ * @hw: main hardware object
+ *
+ * Tranceivers usually have either one transmit framebuffer or one framebuffer
+ * for both transmitting and receiving. Hence, the core currently only handles
+ * one frame at a time for each phy, which means we need to tell upper layers to
+ * stop giving us new skbs while we are busy with the transmitted one. The queue
+ * must then be stopped before transmitting.
+ */
+static void ieee802154_stop_queue(struct ieee802154_hw *hw)
+{
+	struct ieee802154_local *local = hw_to_local(hw);
+	struct ieee802154_sub_if_data *sdata;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(sdata, &local->interfaces, list) {
+		if (!sdata->dev)
+			continue;
+
+		netif_stop_queue(sdata->dev);
+	}
+	rcu_read_unlock();
+}
+
+void ieee802154_hold_queue(struct ieee802154_local *local)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&local->phy->queue_lock, flags);
+	if (!atomic_fetch_inc(&local->phy->hold_txs))
+		ieee802154_stop_queue(&local->hw);
+	spin_unlock_irqrestore(&local->phy->queue_lock, flags);
+}
+
+void ieee802154_release_queue(struct ieee802154_local *local)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&local->phy->queue_lock, flags);
+	if (atomic_dec_and_test(&local->phy->hold_txs))
+		ieee802154_wake_queue(&local->hw);
+	spin_unlock_irqrestore(&local->phy->queue_lock, flags);
+}
+
+void ieee802154_disable_queue(struct ieee802154_local *local)
+{
+	struct ieee802154_sub_if_data *sdata;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(sdata, &local->interfaces, list) {
+		if (!sdata->dev)
+			continue;
+
+		netif_tx_disable(sdata->dev);
+	}
+	rcu_read_unlock();
+}
+
+enum hrtimer_restart ieee802154_xmit_ifs_timer(struct hrtimer *timer)
+{
+	struct ieee802154_local *local =
+		container_of(timer, struct ieee802154_local, ifs_timer);
+
+	ieee802154_release_queue(local);
+
+	return HRTIMER_NORESTART;
+}
+
+void ieee802154_xmit_complete(struct ieee802154_hw *hw, struct sk_buff *skb,
+			      bool ifs_handling)
+{
+	struct ieee802154_local *local = hw_to_local(hw);
+
+	local->tx_result = IEEE802154_SUCCESS;
+
+	if (ifs_handling) {
+		u8 max_sifs_size;
+
+		/* If transceiver sets CRC on his own we need to use lifs
+		 * threshold len above 16 otherwise 18, because it's not
+		 * part of skb->len.
+		 */
+		if (hw->flags & IEEE802154_HW_TX_OMIT_CKSUM)
+			max_sifs_size = IEEE802154_MAX_SIFS_FRAME_SIZE -
+					IEEE802154_FCS_LEN;
+		else
+			max_sifs_size = IEEE802154_MAX_SIFS_FRAME_SIZE;
+
+		if (skb->len > max_sifs_size)
+			hrtimer_start(&local->ifs_timer,
+				      hw->phy->lifs_period * NSEC_PER_USEC,
+				      HRTIMER_MODE_REL);
+		else
+			hrtimer_start(&local->ifs_timer,
+				      hw->phy->sifs_period * NSEC_PER_USEC,
+				      HRTIMER_MODE_REL);
+	} else {
+		ieee802154_release_queue(local);
+	}
+
+	dev_consume_skb_any(skb);
+	if (atomic_dec_and_test(&hw->phy->ongoing_txs))
+		wake_up(&hw->phy->sync_txq);
+}
+EXPORT_SYMBOL(ieee802154_xmit_complete);
+
+void ieee802154_xmit_error(struct ieee802154_hw *hw, struct sk_buff *skb,
+			   int reason)
+{
+	struct ieee802154_local *local = hw_to_local(hw);
+
+	local->tx_result = reason;
+	ieee802154_release_queue(local);
+	dev_kfree_skb_any(skb);
+	if (atomic_dec_and_test(&hw->phy->ongoing_txs))
+		wake_up(&hw->phy->sync_txq);
+}
+EXPORT_SYMBOL(ieee802154_xmit_error);
+
+void ieee802154_xmit_hw_error(struct ieee802154_hw *hw, struct sk_buff *skb)
+{
+	ieee802154_xmit_error(hw, skb, IEEE802154_SYSTEM_ERROR);
+}
+EXPORT_SYMBOL(ieee802154_xmit_hw_error);
+
+void ieee802154_stop_device(struct ieee802154_local *local)
+{
+	flush_workqueue(local->workqueue);
+	hrtimer_cancel(&local->ifs_timer);
+	drv_stop(local);
+}