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, 127 insertions, 0 deletions

diff --git a/net/wireless/of.c b/net/wireless/of.c
new file mode 100644
index 000000000..99acbea3b
--- /dev/null
+++ b/net/wireless/of.c
@@ -0,0 +1,127 @@
+// SPDX-License-Identifier: ISC
+/*
+ * Copyright (C) 2017 Rafał Miłecki <rafal@milecki.pl>
+ */
+
+#include <linux/of.h>
+#include <net/cfg80211.h>
+#include "core.h"
+
+static bool wiphy_freq_limits_valid_chan(struct wiphy *wiphy,
+					 struct ieee80211_freq_range *freq_limits,
+					 unsigned int n_freq_limits,
+					 struct ieee80211_channel *chan)
+{
+	u32 bw = MHZ_TO_KHZ(20);
+	int i;
+
+	for (i = 0; i < n_freq_limits; i++) {
+		struct ieee80211_freq_range *limit = &freq_limits[i];
+
+		if (cfg80211_does_bw_fit_range(limit,
+					       MHZ_TO_KHZ(chan->center_freq),
+					       bw))
+			return true;
+	}
+
+	return false;
+}
+
+static void wiphy_freq_limits_apply(struct wiphy *wiphy,
+				    struct ieee80211_freq_range *freq_limits,
+				    unsigned int n_freq_limits)
+{
+	enum nl80211_band band;
+	int i;
+
+	if (WARN_ON(!n_freq_limits))
+		return;
+
+	for (band = 0; band < NUM_NL80211_BANDS; band++) {
+		struct ieee80211_supported_band *sband = wiphy->bands[band];
+
+		if (!sband)
+			continue;
+
+		for (i = 0; i < sband->n_channels; i++) {
+			struct ieee80211_channel *chan = &sband->channels[i];
+
+			if (chan->flags & IEEE80211_CHAN_DISABLED)
+				continue;
+
+			if (!wiphy_freq_limits_valid_chan(wiphy, freq_limits,
+							  n_freq_limits,
+							  chan)) {
+				pr_debug("Disabling freq %d MHz as it's out of OF limits\n",
+					 chan->center_freq);
+				chan->flags |= IEEE80211_CHAN_DISABLED;
+			}
+		}
+	}
+}
+
+void wiphy_read_of_freq_limits(struct wiphy *wiphy)
+{
+	struct device *dev = wiphy_dev(wiphy);
+	struct device_node *np;
+	struct property *prop;
+	struct ieee80211_freq_range *freq_limits;
+	unsigned int n_freq_limits;
+	const __be32 *p;
+	int len, i;
+	int err = 0;
+
+	if (!dev)
+		return;
+	np = dev_of_node(dev);
+	if (!np)
+		return;
+
+	prop = of_find_property(np, "ieee80211-freq-limit", &len);
+	if (!prop)
+		return;
+
+	if (!len || len % sizeof(u32) || len / sizeof(u32) % 2) {
+		dev_err(dev, "ieee80211-freq-limit wrong format");
+		return;
+	}
+	n_freq_limits = len / sizeof(u32) / 2;
+
+	freq_limits = kzalloc_objs(*freq_limits, n_freq_limits);
+	if (!freq_limits) {
+		err = -ENOMEM;
+		goto out_kfree;
+	}
+
+	p = NULL;
+	for (i = 0; i < n_freq_limits; i++) {
+		struct ieee80211_freq_range *limit = &freq_limits[i];
+
+		p = of_prop_next_u32(prop, p, &limit->start_freq_khz);
+		if (!p) {
+			err = -EINVAL;
+			goto out_kfree;
+		}
+
+		p = of_prop_next_u32(prop, p, &limit->end_freq_khz);
+		if (!p) {
+			err = -EINVAL;
+			goto out_kfree;
+		}
+
+		if (!limit->start_freq_khz ||
+		    !limit->end_freq_khz ||
+		    limit->start_freq_khz >= limit->end_freq_khz) {
+			err = -EINVAL;
+			goto out_kfree;
+		}
+	}
+
+	wiphy_freq_limits_apply(wiphy, freq_limits, n_freq_limits);
+
+out_kfree:
+	kfree(freq_limits);
+	if (err)
+		dev_err(dev, "Failed to get limits: %d\n", err);
+}
+EXPORT_SYMBOL(wiphy_read_of_freq_limits);