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, 354 insertions, 0 deletions

diff --git a/net/mac802154/driver-ops.h b/net/mac802154/driver-ops.h
new file mode 100644
index 000000000..a7af3f0dd
--- /dev/null
+++ b/net/mac802154/driver-ops.h
@@ -0,0 +1,354 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __MAC802154_DRIVER_OPS
+#define __MAC802154_DRIVER_OPS
+
+#include <linux/types.h>
+#include <linux/rtnetlink.h>
+
+#include <net/mac802154.h>
+
+#include "ieee802154_i.h"
+#include "trace.h"
+
+static inline int
+drv_xmit_async(struct ieee802154_local *local, struct sk_buff *skb)
+{
+	return local->ops->xmit_async(&local->hw, skb);
+}
+
+static inline int
+drv_xmit_sync(struct ieee802154_local *local, struct sk_buff *skb)
+{
+	might_sleep();
+
+	return local->ops->xmit_sync(&local->hw, skb);
+}
+
+static inline int drv_set_pan_id(struct ieee802154_local *local, __le16 pan_id)
+{
+	struct ieee802154_hw_addr_filt filt;
+	int ret;
+
+	might_sleep();
+
+	if (!local->ops->set_hw_addr_filt) {
+		WARN_ON(1);
+		return -EOPNOTSUPP;
+	}
+
+	filt.pan_id = pan_id;
+
+	trace_802154_drv_set_pan_id(local, pan_id);
+	ret = local->ops->set_hw_addr_filt(&local->hw, &filt,
+					    IEEE802154_AFILT_PANID_CHANGED);
+	trace_802154_drv_return_int(local, ret);
+	return ret;
+}
+
+static inline int
+drv_set_extended_addr(struct ieee802154_local *local, __le64 extended_addr)
+{
+	struct ieee802154_hw_addr_filt filt;
+	int ret;
+
+	might_sleep();
+
+	if (!local->ops->set_hw_addr_filt) {
+		WARN_ON(1);
+		return -EOPNOTSUPP;
+	}
+
+	filt.ieee_addr = extended_addr;
+
+	trace_802154_drv_set_extended_addr(local, extended_addr);
+	ret = local->ops->set_hw_addr_filt(&local->hw, &filt,
+					    IEEE802154_AFILT_IEEEADDR_CHANGED);
+	trace_802154_drv_return_int(local, ret);
+	return ret;
+}
+
+static inline int
+drv_set_short_addr(struct ieee802154_local *local, __le16 short_addr)
+{
+	struct ieee802154_hw_addr_filt filt;
+	int ret;
+
+	might_sleep();
+
+	if (!local->ops->set_hw_addr_filt) {
+		WARN_ON(1);
+		return -EOPNOTSUPP;
+	}
+
+	filt.short_addr = short_addr;
+
+	trace_802154_drv_set_short_addr(local, short_addr);
+	ret = local->ops->set_hw_addr_filt(&local->hw, &filt,
+					    IEEE802154_AFILT_SADDR_CHANGED);
+	trace_802154_drv_return_int(local, ret);
+	return ret;
+}
+
+static inline int
+drv_set_pan_coord(struct ieee802154_local *local, bool is_coord)
+{
+	struct ieee802154_hw_addr_filt filt;
+	int ret;
+
+	might_sleep();
+
+	if (!local->ops->set_hw_addr_filt) {
+		WARN_ON(1);
+		return -EOPNOTSUPP;
+	}
+
+	filt.pan_coord = is_coord;
+
+	trace_802154_drv_set_pan_coord(local, is_coord);
+	ret = local->ops->set_hw_addr_filt(&local->hw, &filt,
+					    IEEE802154_AFILT_PANC_CHANGED);
+	trace_802154_drv_return_int(local, ret);
+	return ret;
+}
+
+static inline int
+drv_set_promiscuous_mode(struct ieee802154_local *local, bool on)
+{
+	int ret;
+
+	might_sleep();
+
+	if (!local->ops->set_promiscuous_mode) {
+		WARN_ON(1);
+		return -EOPNOTSUPP;
+	}
+
+	trace_802154_drv_set_promiscuous_mode(local, on);
+	ret = local->ops->set_promiscuous_mode(&local->hw, on);
+	trace_802154_drv_return_int(local, ret);
+	return ret;
+}
+
+static inline int drv_start(struct ieee802154_local *local,
+			    enum ieee802154_filtering_level level,
+			    const struct ieee802154_hw_addr_filt *addr_filt)
+{
+	int ret;
+
+	might_sleep();
+
+	/* setup receive mode parameters e.g. address mode */
+	if (local->hw.flags & IEEE802154_HW_AFILT) {
+		ret = drv_set_pan_id(local, addr_filt->pan_id);
+		if (ret < 0)
+			return ret;
+
+		ret = drv_set_short_addr(local, addr_filt->short_addr);
+		if (ret < 0)
+			return ret;
+
+		ret = drv_set_extended_addr(local, addr_filt->ieee_addr);
+		if (ret < 0)
+			return ret;
+	}
+
+	switch (level) {
+	case IEEE802154_FILTERING_NONE:
+		fallthrough;
+	case IEEE802154_FILTERING_1_FCS:
+		fallthrough;
+	case IEEE802154_FILTERING_2_PROMISCUOUS:
+		/* TODO: Requires a different receive mode setup e.g.
+		 * at86rf233 hardware.
+		 */
+		fallthrough;
+	case IEEE802154_FILTERING_3_SCAN:
+		if (local->hw.flags & IEEE802154_HW_PROMISCUOUS) {
+			ret = drv_set_promiscuous_mode(local, true);
+			if (ret < 0)
+				return ret;
+		} else {
+			return -EOPNOTSUPP;
+		}
+
+		/* In practice other filtering levels can be requested, but as
+		 * for now most hardware/drivers only support
+		 * IEEE802154_FILTERING_NONE, we fallback to this actual
+		 * filtering level in hardware and make our own additional
+		 * filtering in mac802154 receive path.
+		 *
+		 * TODO: Move this logic to the device drivers as hardware may
+		 * support more higher level filters. Hardware may also require
+		 * a different order how register are set, which could currently
+		 * be buggy, so all received parameters need to be moved to the
+		 * start() callback and let the driver go into the mode before
+		 * it will turn on receive handling.
+		 */
+		local->phy->filtering = IEEE802154_FILTERING_NONE;
+		break;
+	case IEEE802154_FILTERING_4_FRAME_FIELDS:
+		/* Do not error out if IEEE802154_HW_PROMISCUOUS because we
+		 * expect the hardware to operate at the level
+		 * IEEE802154_FILTERING_4_FRAME_FIELDS anyway.
+		 */
+		if (local->hw.flags & IEEE802154_HW_PROMISCUOUS) {
+			ret = drv_set_promiscuous_mode(local, false);
+			if (ret < 0)
+				return ret;
+		}
+
+		local->phy->filtering = IEEE802154_FILTERING_4_FRAME_FIELDS;
+		break;
+	default:
+		WARN_ON(1);
+		return -EINVAL;
+	}
+
+	trace_802154_drv_start(local);
+	local->started = true;
+	smp_mb();
+	ret = local->ops->start(&local->hw);
+	trace_802154_drv_return_int(local, ret);
+	return ret;
+}
+
+static inline void drv_stop(struct ieee802154_local *local)
+{
+	might_sleep();
+
+	trace_802154_drv_stop(local);
+	local->ops->stop(&local->hw);
+	trace_802154_drv_return_void(local);
+
+	/* sync away all work on the tasklet before clearing started */
+	tasklet_disable(&local->tasklet);
+	tasklet_enable(&local->tasklet);
+
+	barrier();
+
+	local->started = false;
+}
+
+static inline int
+drv_set_channel(struct ieee802154_local *local, u8 page, u8 channel)
+{
+	int ret;
+
+	might_sleep();
+
+	trace_802154_drv_set_channel(local, page, channel);
+	ret = local->ops->set_channel(&local->hw, page, channel);
+	trace_802154_drv_return_int(local, ret);
+	return ret;
+}
+
+static inline int drv_set_tx_power(struct ieee802154_local *local, s32 mbm)
+{
+	int ret;
+
+	might_sleep();
+
+	if (!local->ops->set_txpower) {
+		WARN_ON(1);
+		return -EOPNOTSUPP;
+	}
+
+	trace_802154_drv_set_tx_power(local, mbm);
+	ret = local->ops->set_txpower(&local->hw, mbm);
+	trace_802154_drv_return_int(local, ret);
+	return ret;
+}
+
+static inline int drv_set_cca_mode(struct ieee802154_local *local,
+				   const struct wpan_phy_cca *cca)
+{
+	int ret;
+
+	might_sleep();
+
+	if (!local->ops->set_cca_mode) {
+		WARN_ON(1);
+		return -EOPNOTSUPP;
+	}
+
+	trace_802154_drv_set_cca_mode(local, cca);
+	ret = local->ops->set_cca_mode(&local->hw, cca);
+	trace_802154_drv_return_int(local, ret);
+	return ret;
+}
+
+static inline int drv_set_lbt_mode(struct ieee802154_local *local, bool mode)
+{
+	int ret;
+
+	might_sleep();
+
+	if (!local->ops->set_lbt) {
+		WARN_ON(1);
+		return -EOPNOTSUPP;
+	}
+
+	trace_802154_drv_set_lbt_mode(local, mode);
+	ret = local->ops->set_lbt(&local->hw, mode);
+	trace_802154_drv_return_int(local, ret);
+	return ret;
+}
+
+static inline int
+drv_set_cca_ed_level(struct ieee802154_local *local, s32 mbm)
+{
+	int ret;
+
+	might_sleep();
+
+	if (!local->ops->set_cca_ed_level) {
+		WARN_ON(1);
+		return -EOPNOTSUPP;
+	}
+
+	trace_802154_drv_set_cca_ed_level(local, mbm);
+	ret = local->ops->set_cca_ed_level(&local->hw, mbm);
+	trace_802154_drv_return_int(local, ret);
+	return ret;
+}
+
+static inline int
+drv_set_csma_params(struct ieee802154_local *local, u8 min_be, u8 max_be,
+		    u8 max_csma_backoffs)
+{
+	int ret;
+
+	might_sleep();
+
+	if (!local->ops->set_csma_params) {
+		WARN_ON(1);
+		return -EOPNOTSUPP;
+	}
+
+	trace_802154_drv_set_csma_params(local, min_be, max_be,
+					 max_csma_backoffs);
+	ret = local->ops->set_csma_params(&local->hw, min_be, max_be,
+					   max_csma_backoffs);
+	trace_802154_drv_return_int(local, ret);
+	return ret;
+}
+
+static inline int
+drv_set_max_frame_retries(struct ieee802154_local *local, s8 max_frame_retries)
+{
+	int ret;
+
+	might_sleep();
+
+	if (!local->ops->set_frame_retries) {
+		WARN_ON(1);
+		return -EOPNOTSUPP;
+	}
+
+	trace_802154_drv_set_max_frame_retries(local, max_frame_retries);
+	ret = local->ops->set_frame_retries(&local->hw, max_frame_retries);
+	trace_802154_drv_return_int(local, ret);
+	return ret;
+}
+
+#endif /* __MAC802154_DRIVER_OPS */