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, 215 insertions, 0 deletions

diff --git a/net/mac80211/mesh_sync.c b/net/mac80211/mesh_sync.c
new file mode 100644
index 000000000..24a68eef7
--- /dev/null
+++ b/net/mac80211/mesh_sync.c
@@ -0,0 +1,215 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2011-2012, Pavel Zubarev <pavel.zubarev@gmail.com>
+ * Copyright 2011-2012, Marco Porsch <marco.porsch@s2005.tu-chemnitz.de>
+ * Copyright 2011-2012, cozybit Inc.
+ * Copyright (C) 2021,2023 Intel Corporation
+ */
+
+#include "ieee80211_i.h"
+#include "mesh.h"
+#include "driver-ops.h"
+
+/* This is not in the standard.  It represents a tolerable tsf drift below
+ * which we do no TSF adjustment.
+ */
+#define TOFFSET_MINIMUM_ADJUSTMENT 10
+
+/* This is not in the standard. It is a margin added to the
+ * Toffset setpoint to mitigate TSF overcorrection
+ * introduced by TSF adjustment latency.
+ */
+#define TOFFSET_SET_MARGIN 20
+
+/* This is not in the standard.  It represents the maximum Toffset jump above
+ * which we'll invalidate the Toffset setpoint and choose a new setpoint.  This
+ * could be, for instance, in case a neighbor is restarted and its TSF counter
+ * reset.
+ */
+#define TOFFSET_MAXIMUM_ADJUSTMENT 800		/* 0.8 ms */
+
+struct sync_method {
+	u8 method;
+	struct ieee80211_mesh_sync_ops ops;
+};
+
+/**
+ * mesh_peer_tbtt_adjusting - check if an mp is currently adjusting its TBTT
+ *
+ * @cfg: mesh config element from the mesh peer (or %NULL)
+ *
+ * Returns: If the mesh peer is currently adjusting its TBTT
+ */
+static bool mesh_peer_tbtt_adjusting(const struct ieee80211_meshconf_ie *cfg)
+{
+	return cfg &&
+	       (cfg->meshconf_cap & IEEE80211_MESHCONF_CAPAB_TBTT_ADJUSTING);
+}
+
+void mesh_sync_adjust_tsf(struct ieee80211_sub_if_data *sdata)
+{
+	struct ieee80211_local *local = sdata->local;
+	struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
+	/* sdata->vif.bss_conf.beacon_int in 1024us units, 0.04% */
+	u64 beacon_int_fraction = sdata->vif.bss_conf.beacon_int * 1024 / 2500;
+	u64 tsf;
+	u64 tsfdelta;
+
+	spin_lock_bh(&ifmsh->sync_offset_lock);
+	if (ifmsh->sync_offset_clockdrift_max < beacon_int_fraction) {
+		msync_dbg(sdata, "TSF : max clockdrift=%lld; adjusting\n",
+			  (long long) ifmsh->sync_offset_clockdrift_max);
+		tsfdelta = -ifmsh->sync_offset_clockdrift_max;
+		ifmsh->sync_offset_clockdrift_max = 0;
+	} else {
+		msync_dbg(sdata, "TSF : max clockdrift=%lld; adjusting by %llu\n",
+			  (long long) ifmsh->sync_offset_clockdrift_max,
+			  (unsigned long long) beacon_int_fraction);
+		tsfdelta = -beacon_int_fraction;
+		ifmsh->sync_offset_clockdrift_max -= beacon_int_fraction;
+	}
+	spin_unlock_bh(&ifmsh->sync_offset_lock);
+
+	if (local->ops->offset_tsf) {
+		drv_offset_tsf(local, sdata, tsfdelta);
+	} else {
+		tsf = drv_get_tsf(local, sdata);
+		if (tsf != -1ULL)
+			drv_set_tsf(local, sdata, tsf + tsfdelta);
+	}
+}
+
+static void
+mesh_sync_offset_rx_bcn_presp(struct ieee80211_sub_if_data *sdata, u16 stype,
+			      struct ieee80211_mgmt *mgmt, unsigned int len,
+			      const struct ieee80211_meshconf_ie *mesh_cfg,
+			      struct ieee80211_rx_status *rx_status)
+{
+	struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
+	struct ieee80211_local *local = sdata->local;
+	struct sta_info *sta;
+	u64 t_t, t_r;
+
+	WARN_ON(ifmsh->mesh_sp_id != IEEE80211_SYNC_METHOD_NEIGHBOR_OFFSET);
+
+	/* standard mentions only beacons */
+	if (stype != IEEE80211_STYPE_BEACON)
+		return;
+
+	/*
+	 * Get time when timestamp field was received.  If we don't
+	 * have rx timestamps, then use current tsf as an approximation.
+	 * drv_get_tsf() must be called before entering the rcu-read
+	 * section.
+	 */
+	if (ieee80211_have_rx_timestamp(rx_status))
+		t_r = ieee80211_calculate_rx_timestamp(&local->hw, rx_status,
+						       len + FCS_LEN, 24);
+	else
+		t_r = drv_get_tsf(local, sdata);
+
+	rcu_read_lock();
+	sta = sta_info_get(sdata, mgmt->sa);
+	if (!sta)
+		goto no_sync;
+
+	/* check offset sync conditions (13.13.2.2.1)
+	 *
+	 * TODO also sync to
+	 * dot11MeshNbrOffsetMaxNeighbor non-peer non-MBSS neighbors
+	 */
+
+	if (mesh_peer_tbtt_adjusting(mesh_cfg)) {
+		msync_dbg(sdata, "STA %pM : is adjusting TBTT\n",
+			  sta->sta.addr);
+		goto no_sync;
+	}
+
+	/* Timing offset calculation (see 13.13.2.2.2) */
+	t_t = le64_to_cpu(mgmt->u.beacon.timestamp);
+	sta->mesh->t_offset = t_t - t_r;
+
+	if (test_sta_flag(sta, WLAN_STA_TOFFSET_KNOWN)) {
+		s64 t_clockdrift = sta->mesh->t_offset_setpoint - sta->mesh->t_offset;
+		msync_dbg(sdata,
+			  "STA %pM : t_offset=%lld, t_offset_setpoint=%lld, t_clockdrift=%lld\n",
+			  sta->sta.addr, (long long) sta->mesh->t_offset,
+			  (long long) sta->mesh->t_offset_setpoint,
+			  (long long) t_clockdrift);
+
+		if (t_clockdrift > TOFFSET_MAXIMUM_ADJUSTMENT ||
+		    t_clockdrift < -TOFFSET_MAXIMUM_ADJUSTMENT) {
+			msync_dbg(sdata,
+				  "STA %pM : t_clockdrift=%lld too large, setpoint reset\n",
+				  sta->sta.addr,
+				  (long long) t_clockdrift);
+			clear_sta_flag(sta, WLAN_STA_TOFFSET_KNOWN);
+			goto no_sync;
+		}
+
+		spin_lock_bh(&ifmsh->sync_offset_lock);
+		if (t_clockdrift > ifmsh->sync_offset_clockdrift_max)
+			ifmsh->sync_offset_clockdrift_max = t_clockdrift;
+		spin_unlock_bh(&ifmsh->sync_offset_lock);
+	} else {
+		sta->mesh->t_offset_setpoint = sta->mesh->t_offset - TOFFSET_SET_MARGIN;
+		set_sta_flag(sta, WLAN_STA_TOFFSET_KNOWN);
+		msync_dbg(sdata,
+			  "STA %pM : offset was invalid, t_offset=%lld\n",
+			  sta->sta.addr,
+			  (long long) sta->mesh->t_offset);
+	}
+
+no_sync:
+	rcu_read_unlock();
+}
+
+static void mesh_sync_offset_adjust_tsf(struct ieee80211_sub_if_data *sdata,
+					 struct beacon_data *beacon)
+{
+	struct ieee80211_if_mesh *ifmsh = &sdata->u.mesh;
+
+	WARN_ON(ifmsh->mesh_sp_id != IEEE80211_SYNC_METHOD_NEIGHBOR_OFFSET);
+	WARN_ON(!rcu_read_lock_held());
+
+	spin_lock_bh(&ifmsh->sync_offset_lock);
+
+	if (ifmsh->sync_offset_clockdrift_max > TOFFSET_MINIMUM_ADJUSTMENT) {
+		/* Since adjusting the tsf here would
+		 * require a possibly blocking call
+		 * to the driver tsf setter, we punt
+		 * the tsf adjustment to the mesh tasklet
+		 */
+		msync_dbg(sdata,
+			  "TSF : kicking off TSF adjustment with clockdrift_max=%lld\n",
+			  ifmsh->sync_offset_clockdrift_max);
+		set_bit(MESH_WORK_DRIFT_ADJUST, &ifmsh->wrkq_flags);
+	} else {
+		msync_dbg(sdata,
+			  "TSF : max clockdrift=%lld; too small to adjust\n",
+			  (long long)ifmsh->sync_offset_clockdrift_max);
+		ifmsh->sync_offset_clockdrift_max = 0;
+	}
+	spin_unlock_bh(&ifmsh->sync_offset_lock);
+}
+
+static const struct sync_method sync_methods[] = {
+	{
+		.method = IEEE80211_SYNC_METHOD_NEIGHBOR_OFFSET,
+		.ops = {
+			.rx_bcn_presp = &mesh_sync_offset_rx_bcn_presp,
+			.adjust_tsf = &mesh_sync_offset_adjust_tsf,
+		}
+	},
+};
+
+const struct ieee80211_mesh_sync_ops *ieee80211_mesh_sync_ops_get(u8 method)
+{
+	int i;
+
+	for (i = 0 ; i < ARRAY_SIZE(sync_methods); ++i) {
+		if (sync_methods[i].method == method)
+			return &sync_methods[i].ops;
+	}
+	return NULL;
+}