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, 308 insertions, 0 deletions

diff --git a/net/mac802154/main.c b/net/mac802154/main.c
new file mode 100644
index 000000000..ea1efef35
--- /dev/null
+++ b/net/mac802154/main.c
@@ -0,0 +1,308 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2007-2012 Siemens AG
+ *
+ * Written by:
+ * Alexander Smirnov <alex.bluesman.smirnov@gmail.com>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/netdevice.h>
+
+#include <net/netlink.h>
+#include <net/nl802154.h>
+#include <net/mac802154.h>
+#include <net/ieee802154_netdev.h>
+#include <net/route.h>
+#include <net/cfg802154.h>
+
+#include "ieee802154_i.h"
+#include "cfg.h"
+
+static void ieee802154_tasklet_handler(struct tasklet_struct *t)
+{
+	struct ieee802154_local *local = from_tasklet(local, t, tasklet);
+	struct sk_buff *skb;
+
+	while ((skb = skb_dequeue(&local->skb_queue))) {
+		switch (skb->pkt_type) {
+		case IEEE802154_RX_MSG:
+			/* Clear skb->pkt_type in order to not confuse kernel
+			 * netstack.
+			 */
+			skb->pkt_type = 0;
+			ieee802154_rx(local, skb);
+			break;
+		default:
+			WARN(1, "mac802154: Packet is of unknown type %d\n",
+			     skb->pkt_type);
+			kfree_skb(skb);
+			break;
+		}
+	}
+}
+
+struct ieee802154_hw *
+ieee802154_alloc_hw(size_t priv_data_len, const struct ieee802154_ops *ops)
+{
+	struct wpan_phy *phy;
+	struct ieee802154_local *local;
+	size_t priv_size;
+
+	if (WARN_ON(!ops || !(ops->xmit_async || ops->xmit_sync) || !ops->ed ||
+		    !ops->start || !ops->stop || !ops->set_channel))
+		return NULL;
+
+	/* Ensure 32-byte alignment of our private data and hw private data.
+	 * We use the wpan_phy priv data for both our ieee802154_local and for
+	 * the driver's private data
+	 *
+	 * in memory it'll be like this:
+	 *
+	 * +-------------------------+
+	 * | struct wpan_phy         |
+	 * +-------------------------+
+	 * | struct ieee802154_local |
+	 * +-------------------------+
+	 * | driver's private data   |
+	 * +-------------------------+
+	 *
+	 * Due to ieee802154 layer isn't aware of driver and MAC structures,
+	 * so lets align them here.
+	 */
+
+	priv_size = ALIGN(sizeof(*local), NETDEV_ALIGN) + priv_data_len;
+
+	phy = wpan_phy_new(&mac802154_config_ops, priv_size);
+	if (!phy) {
+		pr_err("failure to allocate master IEEE802.15.4 device\n");
+		return NULL;
+	}
+
+	phy->privid = mac802154_wpan_phy_privid;
+
+	local = wpan_phy_priv(phy);
+	local->phy = phy;
+	local->hw.phy = local->phy;
+	local->hw.priv = (char *)local + ALIGN(sizeof(*local), NETDEV_ALIGN);
+	local->ops = ops;
+
+	INIT_LIST_HEAD(&local->interfaces);
+	INIT_LIST_HEAD(&local->rx_beacon_list);
+	INIT_LIST_HEAD(&local->rx_mac_cmd_list);
+	mutex_init(&local->iflist_mtx);
+
+	tasklet_setup(&local->tasklet, ieee802154_tasklet_handler);
+
+	skb_queue_head_init(&local->skb_queue);
+
+	INIT_WORK(&local->sync_tx_work, ieee802154_xmit_sync_worker);
+	INIT_DELAYED_WORK(&local->scan_work, mac802154_scan_worker);
+	INIT_WORK(&local->rx_beacon_work, mac802154_rx_beacon_worker);
+	INIT_DELAYED_WORK(&local->beacon_work, mac802154_beacon_worker);
+	INIT_WORK(&local->rx_mac_cmd_work, mac802154_rx_mac_cmd_worker);
+
+	init_completion(&local->assoc_done);
+
+	/* init supported flags with 802.15.4 default ranges */
+	phy->supported.max_minbe = 8;
+	phy->supported.min_maxbe = 3;
+	phy->supported.max_maxbe = 8;
+	phy->supported.min_frame_retries = 0;
+	phy->supported.max_frame_retries = 7;
+	phy->supported.max_csma_backoffs = 5;
+	phy->supported.lbt = NL802154_SUPPORTED_BOOL_FALSE;
+
+	/* always supported */
+	phy->supported.iftypes = BIT(NL802154_IFTYPE_NODE) | BIT(NL802154_IFTYPE_COORD);
+
+	return &local->hw;
+}
+EXPORT_SYMBOL(ieee802154_alloc_hw);
+
+void ieee802154_configure_durations(struct wpan_phy *phy,
+				    unsigned int page, unsigned int channel)
+{
+	u32 duration = 0;
+
+	switch (page) {
+	case 0:
+		if (BIT(channel) & 0x1)
+			/* 868 MHz BPSK 802.15.4-2003: 20 ksym/s */
+			duration = 50 * NSEC_PER_USEC;
+		else if (BIT(channel) & 0x7FE)
+			/* 915 MHz BPSK	802.15.4-2003: 40 ksym/s */
+			duration = 25 * NSEC_PER_USEC;
+		else if (BIT(channel) & 0x7FFF800)
+			/* 2400 MHz O-QPSK 802.15.4-2006: 62.5 ksym/s */
+			duration = 16 * NSEC_PER_USEC;
+		break;
+	case 2:
+		if (BIT(channel) & 0x1)
+			/* 868 MHz O-QPSK 802.15.4-2006: 25 ksym/s */
+			duration = 40 * NSEC_PER_USEC;
+		else if (BIT(channel) & 0x7FE)
+			/* 915 MHz O-QPSK 802.15.4-2006: 62.5 ksym/s */
+			duration = 16 * NSEC_PER_USEC;
+		break;
+	case 3:
+		if (BIT(channel) & 0x3FFF)
+			/* 2.4 GHz CSS 802.15.4a-2007: 1/6 Msym/s */
+			duration = 6 * NSEC_PER_USEC;
+		break;
+	default:
+		break;
+	}
+
+	if (!duration) {
+		pr_debug("Unknown PHY symbol duration\n");
+		return;
+	}
+
+	phy->symbol_duration = duration;
+	phy->lifs_period =
+		(IEEE802154_LIFS_PERIOD * phy->symbol_duration) / NSEC_PER_USEC;
+	phy->sifs_period =
+		(IEEE802154_SIFS_PERIOD * phy->symbol_duration) / NSEC_PER_USEC;
+}
+EXPORT_SYMBOL(ieee802154_configure_durations);
+
+void ieee802154_free_hw(struct ieee802154_hw *hw)
+{
+	struct ieee802154_local *local = hw_to_local(hw);
+
+	BUG_ON(!list_empty(&local->interfaces));
+
+	mutex_destroy(&local->iflist_mtx);
+
+	wpan_phy_free(local->phy);
+}
+EXPORT_SYMBOL(ieee802154_free_hw);
+
+static void ieee802154_setup_wpan_phy_pib(struct wpan_phy *wpan_phy)
+{
+	/* TODO warn on empty symbol_duration
+	 * Should be done when all drivers sets this value.
+	 */
+
+	wpan_phy->lifs_period =	(IEEE802154_LIFS_PERIOD *
+				 wpan_phy->symbol_duration) / NSEC_PER_USEC;
+	wpan_phy->sifs_period =	(IEEE802154_SIFS_PERIOD *
+				 wpan_phy->symbol_duration) / NSEC_PER_USEC;
+}
+
+int ieee802154_register_hw(struct ieee802154_hw *hw)
+{
+	struct ieee802154_local *local = hw_to_local(hw);
+	char mac_wq_name[IFNAMSIZ + 10] = {};
+	struct net_device *dev;
+	int rc = -ENOSYS;
+
+	local->workqueue =
+		create_singlethread_workqueue(wpan_phy_name(local->phy));
+	if (!local->workqueue) {
+		rc = -ENOMEM;
+		goto out;
+	}
+
+	snprintf(mac_wq_name, IFNAMSIZ + 10, "%s-mac-cmds", wpan_phy_name(local->phy));
+	local->mac_wq =	create_singlethread_workqueue(mac_wq_name);
+	if (!local->mac_wq) {
+		rc = -ENOMEM;
+		goto out_wq;
+	}
+
+	hrtimer_setup(&local->ifs_timer, ieee802154_xmit_ifs_timer, CLOCK_MONOTONIC,
+		      HRTIMER_MODE_REL);
+
+	wpan_phy_set_dev(local->phy, local->hw.parent);
+
+	ieee802154_setup_wpan_phy_pib(local->phy);
+
+	ieee802154_configure_durations(local->phy, local->phy->current_page,
+				       local->phy->current_channel);
+
+	if (!(hw->flags & IEEE802154_HW_CSMA_PARAMS)) {
+		local->phy->supported.min_csma_backoffs = 4;
+		local->phy->supported.max_csma_backoffs = 4;
+		local->phy->supported.min_maxbe = 5;
+		local->phy->supported.max_maxbe = 5;
+		local->phy->supported.min_minbe = 3;
+		local->phy->supported.max_minbe = 3;
+	}
+
+	if (!(hw->flags & IEEE802154_HW_FRAME_RETRIES)) {
+		local->phy->supported.min_frame_retries = 3;
+		local->phy->supported.max_frame_retries = 3;
+	}
+
+	if (hw->flags & IEEE802154_HW_PROMISCUOUS)
+		local->phy->supported.iftypes |= BIT(NL802154_IFTYPE_MONITOR);
+
+	rc = wpan_phy_register(local->phy);
+	if (rc < 0)
+		goto out_mac_wq;
+
+	rtnl_lock();
+
+	dev = ieee802154_if_add(local, "wpan%d", NET_NAME_ENUM,
+				NL802154_IFTYPE_NODE,
+				cpu_to_le64(0x0000000000000000ULL));
+	if (IS_ERR(dev)) {
+		rtnl_unlock();
+		rc = PTR_ERR(dev);
+		goto out_phy;
+	}
+
+	rtnl_unlock();
+
+	return 0;
+
+out_phy:
+	wpan_phy_unregister(local->phy);
+out_mac_wq:
+	destroy_workqueue(local->mac_wq);
+out_wq:
+	destroy_workqueue(local->workqueue);
+out:
+	return rc;
+}
+EXPORT_SYMBOL(ieee802154_register_hw);
+
+void ieee802154_unregister_hw(struct ieee802154_hw *hw)
+{
+	struct ieee802154_local *local = hw_to_local(hw);
+
+	tasklet_kill(&local->tasklet);
+	flush_workqueue(local->workqueue);
+
+	rtnl_lock();
+
+	ieee802154_remove_interfaces(local);
+
+	rtnl_unlock();
+
+	destroy_workqueue(local->mac_wq);
+	destroy_workqueue(local->workqueue);
+	wpan_phy_unregister(local->phy);
+}
+EXPORT_SYMBOL(ieee802154_unregister_hw);
+
+static int __init ieee802154_init(void)
+{
+	return ieee802154_iface_init();
+}
+
+static void __exit ieee802154_exit(void)
+{
+	ieee802154_iface_exit();
+
+	rcu_barrier();
+}
+
+subsys_initcall(ieee802154_init);
+module_exit(ieee802154_exit);
+
+MODULE_DESCRIPTION("IEEE 802.15.4 subsystem");
+MODULE_LICENSE("GPL v2");