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, 139 insertions, 0 deletions

diff --git a/net/mac80211/drop.h b/net/mac80211/drop.h
new file mode 100644
index 000000000..f06a8aa90
--- /dev/null
+++ b/net/mac80211/drop.h
@@ -0,0 +1,139 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * mac80211 drop reason list
+ *
+ * Copyright (C) 2023-2024, 2026 Intel Corporation
+ */
+
+#ifndef MAC80211_DROP_H
+#define MAC80211_DROP_H
+#include <net/dropreason.h>
+
+typedef unsigned int __bitwise ieee80211_rx_result;
+
+#define MAC80211_DROP_REASONS_UNUSABLE(R)	\
+	/* 0x00 == ___RX_DROP_UNUSABLE */	\
+	R(RX_DROP_U_MIC_FAIL)			\
+	R(RX_DROP_U_REPLAY)			\
+	R(RX_DROP_U_BAD_MMIE)			\
+	R(RX_DROP_U_DUP)			\
+	R(RX_DROP_U_SPURIOUS)			\
+	R(RX_DROP_U_DECRYPT_FAIL)		\
+	R(RX_DROP_U_NO_KEY_ID)			\
+	R(RX_DROP_U_BAD_CIPHER)			\
+	R(RX_DROP_U_OOM)			\
+	R(RX_DROP_U_NONSEQ_PN)			\
+	R(RX_DROP_U_BAD_KEY_COLOR)		\
+	R(RX_DROP_U_BAD_4ADDR)			\
+	R(RX_DROP_U_BAD_AMSDU)			\
+	R(RX_DROP_U_BAD_AMSDU_CIPHER)		\
+	R(RX_DROP_U_INVALID_8023)		\
+	/* 0x10 */				\
+	R(RX_DROP_U_RUNT_ACTION)		\
+	R(RX_DROP_U_UNPROT_ACTION)		\
+	R(RX_DROP_U_UNPROT_DUAL)		\
+	R(RX_DROP_U_UNPROT_UCAST_MGMT)		\
+	R(RX_DROP_U_UNPROT_MCAST_MGMT)		\
+	R(RX_DROP_U_UNPROT_BEACON)		\
+	R(RX_DROP_U_UNPROT_UNICAST_PUB_ACTION)	\
+	R(RX_DROP_U_UNPROT_ROBUST_ACTION)	\
+	R(RX_DROP_U_ACTION_UNKNOWN_SRC)		\
+	R(RX_DROP_U_REJECTED_ACTION_RESPONSE)	\
+	R(RX_DROP_U_EXPECT_DEFRAG_PROT)		\
+	R(RX_DROP_U_WEP_DEC_FAIL)		\
+	R(RX_DROP_U_NO_IV)			\
+	R(RX_DROP_U_NO_ICV)			\
+	R(RX_DROP_U_AP_RX_GROUPCAST)		\
+	R(RX_DROP_U_SHORT_MMIC)			\
+	/* 0x20 */				\
+	R(RX_DROP_U_MMIC_FAIL)			\
+	R(RX_DROP_U_SHORT_TKIP)			\
+	R(RX_DROP_U_TKIP_FAIL)			\
+	R(RX_DROP_U_SHORT_CCMP)			\
+	R(RX_DROP_U_SHORT_CCMP_MIC)		\
+	R(RX_DROP_U_SHORT_GCMP)			\
+	R(RX_DROP_U_SHORT_GCMP_MIC)		\
+	R(RX_DROP_U_SHORT_CMAC)			\
+	R(RX_DROP_U_SHORT_CMAC256)		\
+	R(RX_DROP_U_SHORT_GMAC)			\
+	R(RX_DROP_U_UNEXPECTED_VLAN_4ADDR)	\
+	R(RX_DROP_U_UNEXPECTED_STA_4ADDR)	\
+	R(RX_DROP_U_UNEXPECTED_VLAN_MCAST)	\
+	R(RX_DROP_U_NOT_PORT_CONTROL)		\
+	R(RX_DROP_U_UNEXPECTED_4ADDR_FRAME)	\
+	R(RX_DROP_U_BAD_BCN_KEYIDX)		\
+	/* 0x30 */				\
+	R(RX_DROP_U_BAD_MGMT_KEYIDX)		\
+	R(RX_DROP_U_UNKNOWN_ACTION_REJECTED)	\
+	R(RX_DROP_U_MESH_DS_BITS)		\
+	R(RX_DROP_U_MESH_A3_MISMATCH)		\
+	R(RX_DROP_U_MESH_NO_A4)			\
+	R(RX_DROP_U_MESH_A4_MISMATCH)		\
+	R(RX_DROP_U_MESH_UNEXP_DATA)		\
+	R(RX_DROP_U_MESH_WRONG_ACTION)		\
+	R(RX_DROP_U_MESH_UNEXP_MGMT)		\
+	R(RX_DROP_U_SPURIOUS_NOTIF)		\
+	R(RX_DROP_U_RUNT_DATA)			\
+	R(RX_DROP_U_KEY_TAINTED)		\
+	R(RX_DROP_U_UNPROTECTED)		\
+	R(RX_DROP_U_MCAST_FRAGMENT)		\
+	R(RX_DROP_U_DEFRAG_MISMATCH)		\
+	R(RX_DROP_U_RUNT_MESH_DATA)		\
+	/* 0x40 */				\
+	R(RX_DROP_U_MESH_NO_TTL)		\
+	R(RX_DROP_U_MESH_RMC)			\
+	R(RX_DROP_U_MESH_BAD_AE)		\
+	R(RX_DROP_U_MESH_TTL_EXPIRED)		\
+	R(RX_DROP_U_MESH_NOT_FORWARDING)	\
+	R(RX_DROP_U_AMSDU_WITHOUT_DATA)		\
+	R(RX_DROP_U_NULL_DATA)			\
+	R(RX_DROP_U_UNEXPECTED_4ADDR)		\
+	R(RX_DROP_U_PORT_CONTROL)		\
+	R(RX_DROP_U_UNKNOWN_STA)		\
+	R(RX_DROP_U_RUNT_BAR)			\
+	R(RX_DROP_U_BAR_OUTSIDE_SESSION)	\
+	R(RX_DROP_U_CTRL_FRAME)			\
+	R(RX_DROP_U_RUNT_MGMT)			\
+	R(RX_DROP_U_EXPECTED_MGMT)		\
+	R(RX_DROP_U_NONBCAST_BEACON)		\
+	/* 0x50 */				\
+	R(RX_DROP_U_MALFORMED_ACTION)		\
+	R(RX_DROP_U_UNKNOWN_MCAST_ACTION)	\
+	R(RX_DROP_U_UNEXPECTED_EXT_FRAME)	\
+	R(RX_DROP_U_UNHANDLED_MGMT)		\
+	R(RX_DROP_U_MCAST_DEAUTH)		\
+	R(RX_DROP_U_UNHANDLED_DEAUTH)		\
+	R(RX_DROP_U_MCAST_DISASSOC)		\
+	R(RX_DROP_U_UNHANDLED_DISASSOC)		\
+	R(RX_DROP_U_UNHANDLED_PREQ)		\
+	R(RX_DROP_U_UNHANDLED_MGMT_STYPE)	\
+	R(RX_DROP_U_NO_LINK)			\
+/* this line for the trailing \ - add before this */
+
+/* having two enums allows for checking ieee80211_rx_result use with sparse */
+enum ___mac80211_drop_reason {
+/* if we get to the end of handlers with RX_CONTINUE this will be the reason */
+	___RX_CONTINUE	= SKB_CONSUMED,
+
+/* this never gets used as an argument to kfree_skb_reason() */
+	___RX_QUEUED	= SKB_NOT_DROPPED_YET,
+
+#define ENUM(x) ___ ## x,
+	___RX_DROP_UNUSABLE = SKB_DROP_REASON_SUBSYS_MAC80211_UNUSABLE <<
+		SKB_DROP_REASON_SUBSYS_SHIFT,
+	MAC80211_DROP_REASONS_UNUSABLE(ENUM)
+#undef ENUM
+};
+
+enum mac80211_drop_reason {
+	RX_CONTINUE	= (__force ieee80211_rx_result)___RX_CONTINUE,
+	RX_QUEUED	= (__force ieee80211_rx_result)___RX_QUEUED,
+#define DEF(x) x = (__force ieee80211_rx_result)___ ## x,
+	MAC80211_DROP_REASONS_UNUSABLE(DEF)
+#undef DEF
+};
+
+#define RX_RES_IS_UNUSABLE(result)	\
+	(((__force u32)(result) & SKB_DROP_REASON_SUBSYS_MASK) == ___RX_DROP_UNUSABLE)
+
+#endif /* MAC80211_DROP_H */