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, 112 insertions, 0 deletions

diff --git a/net/mac80211/rate.h b/net/mac80211/rate.h
new file mode 100644
index 000000000..5e4bde598
--- /dev/null
+++ b/net/mac80211/rate.h
@@ -0,0 +1,112 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2002-2005, Instant802 Networks, Inc.
+ * Copyright 2005, Devicescape Software, Inc.
+ * Copyright (c) 2006 Jiri Benc <jbenc@suse.cz>
+ * Copyright (C) 2022, 2024 Intel Corporation
+ */
+
+#ifndef IEEE80211_RATE_H
+#define IEEE80211_RATE_H
+
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/types.h>
+#include <net/mac80211.h>
+#include "ieee80211_i.h"
+#include "sta_info.h"
+#include "driver-ops.h"
+
+struct rate_control_ref {
+	const struct rate_control_ops *ops;
+	void *priv;
+};
+
+void rate_control_get_rate(struct ieee80211_sub_if_data *sdata,
+			   struct sta_info *sta,
+			   struct ieee80211_tx_rate_control *txrc);
+
+void rate_control_tx_status(struct ieee80211_local *local,
+			    struct ieee80211_tx_status *st);
+
+void rate_control_rate_init(struct link_sta_info *link_sta);
+void rate_control_rate_init_all_links(struct sta_info *sta);
+void rate_control_rate_update(struct ieee80211_local *local,
+			      struct ieee80211_supported_band *sband,
+			      struct link_sta_info *link_sta,
+			      u32 changed);
+
+static inline void *rate_control_alloc_sta(struct rate_control_ref *ref,
+					   struct sta_info *sta, gfp_t gfp)
+{
+	spin_lock_init(&sta->rate_ctrl_lock);
+	return ref->ops->alloc_sta(ref->priv, &sta->sta, gfp);
+}
+
+static inline void rate_control_free_sta(struct sta_info *sta)
+{
+	struct rate_control_ref *ref = sta->rate_ctrl;
+	struct ieee80211_sta *ista = &sta->sta;
+	void *priv_sta = sta->rate_ctrl_priv;
+
+	ref->ops->free_sta(ref->priv, ista, priv_sta);
+}
+
+static inline void rate_control_add_sta_debugfs(struct sta_info *sta)
+{
+#ifdef CONFIG_MAC80211_DEBUGFS
+	struct rate_control_ref *ref = sta->rate_ctrl;
+	if (ref && sta->debugfs_dir && ref->ops->add_sta_debugfs)
+		ref->ops->add_sta_debugfs(ref->priv, sta->rate_ctrl_priv,
+					  sta->debugfs_dir);
+#endif
+}
+
+extern const struct debugfs_short_fops rcname_ops;
+
+static inline void rate_control_add_debugfs(struct ieee80211_local *local)
+{
+#ifdef CONFIG_MAC80211_DEBUGFS
+	struct dentry *debugfsdir;
+
+	if (!local->rate_ctrl)
+		return;
+
+	if (!local->rate_ctrl->ops->add_debugfs)
+		return;
+
+	debugfsdir = debugfs_create_dir("rc", local->hw.wiphy->debugfsdir);
+	local->debugfs.rcdir = debugfsdir;
+	debugfs_create_file("name", 0400, debugfsdir,
+			    local->rate_ctrl, &rcname_ops);
+
+	local->rate_ctrl->ops->add_debugfs(&local->hw, local->rate_ctrl->priv,
+					   debugfsdir);
+#endif
+}
+
+void ieee80211_check_rate_mask(struct ieee80211_link_data *link);
+
+/* Get a reference to the rate control algorithm. If `name' is NULL, get the
+ * first available algorithm. */
+int ieee80211_init_rate_ctrl_alg(struct ieee80211_local *local,
+				 const char *name);
+void rate_control_deinitialize(struct ieee80211_local *local);
+
+
+/* Rate control algorithms */
+#ifdef CONFIG_MAC80211_RC_MINSTREL
+int rc80211_minstrel_init(void);
+void rc80211_minstrel_exit(void);
+#else
+static inline int rc80211_minstrel_init(void)
+{
+	return 0;
+}
+static inline void rc80211_minstrel_exit(void)
+{
+}
+#endif
+
+
+#endif /* IEEE80211_RATE_H */