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, 66 insertions, 0 deletions

diff --git a/net/wireless/tests/util.h b/net/wireless/tests/util.h
new file mode 100644
index 000000000..6de712e0d
--- /dev/null
+++ b/net/wireless/tests/util.h
@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Utilities for cfg80211 unit testing
+ *
+ * Copyright (C) 2023 Intel Corporation
+ */
+#ifndef __CFG80211_UTILS_H
+#define __CFG80211_UTILS_H
+
+#define CHAN2G(_freq)  { \
+	.band = NL80211_BAND_2GHZ, \
+	.center_freq = (_freq), \
+	.hw_value = (_freq), \
+}
+
+static const struct ieee80211_channel channels_2ghz[] = {
+	CHAN2G(2412), /* Channel 1 */
+	CHAN2G(2417), /* Channel 2 */
+	CHAN2G(2422), /* Channel 3 */
+	CHAN2G(2427), /* Channel 4 */
+	CHAN2G(2432), /* Channel 5 */
+	CHAN2G(2437), /* Channel 6 */
+	CHAN2G(2442), /* Channel 7 */
+	CHAN2G(2447), /* Channel 8 */
+	CHAN2G(2452), /* Channel 9 */
+	CHAN2G(2457), /* Channel 10 */
+	CHAN2G(2462), /* Channel 11 */
+	CHAN2G(2467), /* Channel 12 */
+	CHAN2G(2472), /* Channel 13 */
+	CHAN2G(2484), /* Channel 14 */
+};
+
+struct t_wiphy_priv {
+	struct kunit *test;
+	struct cfg80211_ops *ops;
+
+	void *ctx;
+
+	struct ieee80211_supported_band band_2ghz;
+	struct ieee80211_channel channels_2ghz[ARRAY_SIZE(channels_2ghz)];
+};
+
+#define T_WIPHY(test, ctx) ({						\
+		struct wiphy *__wiphy =					\
+			kunit_alloc_resource(test, t_wiphy_init,	\
+					     t_wiphy_exit,		\
+					     GFP_KERNEL, &(ctx));	\
+									\
+		KUNIT_ASSERT_NOT_NULL(test, __wiphy);			\
+		__wiphy;						\
+	})
+#define t_wiphy_ctx(wiphy) (((struct t_wiphy_priv *)wiphy_priv(wiphy))->ctx)
+
+int t_wiphy_init(struct kunit_resource *resource, void *data);
+void t_wiphy_exit(struct kunit_resource *resource);
+
+#define t_skb_remove_member(skb, type, member)	do {				\
+		memmove((skb)->data + (skb)->len - sizeof(type) +		\
+			offsetof(type, member),					\
+			(skb)->data + (skb)->len - sizeof(type) +		\
+			offsetofend(type, member),				\
+			offsetofend(type, member));				\
+		skb_trim(skb, (skb)->len - sizeof_field(type, member));		\
+	} while (0)
+
+#endif /* __CFG80211_UTILS_H */