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, 305 insertions, 0 deletions

diff --git a/net/nfc/nci/data.c b/net/nfc/nci/data.c
new file mode 100644
index 000000000..5f98c73db
--- /dev/null
+++ b/net/nfc/nci/data.c
@@ -0,0 +1,305 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  The NFC Controller Interface is the communication protocol between an
+ *  NFC Controller (NFCC) and a Device Host (DH).
+ *
+ *  Copyright (C) 2011 Texas Instruments, Inc.
+ *  Copyright (C) 2014 Marvell International Ltd.
+ *
+ *  Written by Ilan Elias <ilane@ti.com>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": %s: " fmt, __func__
+
+#include <linux/types.h>
+#include <linux/interrupt.h>
+#include <linux/wait.h>
+#include <linux/bitops.h>
+#include <linux/skbuff.h>
+
+#include "../nfc.h"
+#include <net/nfc/nci.h>
+#include <net/nfc/nci_core.h>
+#include <linux/nfc.h>
+
+/* Complete data exchange transaction and forward skb to nfc core */
+void nci_data_exchange_complete(struct nci_dev *ndev, struct sk_buff *skb,
+				__u8 conn_id, int err)
+{
+	const struct nci_conn_info *conn_info;
+	data_exchange_cb_t cb;
+	void *cb_context;
+
+	conn_info = nci_get_conn_info_by_conn_id(ndev, conn_id);
+	if (!conn_info) {
+		kfree_skb(skb);
+		clear_bit(NCI_DATA_EXCHANGE, &ndev->flags);
+		return;
+	}
+
+	cb = conn_info->data_exchange_cb;
+	cb_context = conn_info->data_exchange_cb_context;
+
+	pr_debug("len %d, err %d\n", skb ? skb->len : 0, err);
+
+	/* data exchange is complete, stop the data timer */
+	timer_delete_sync(&ndev->data_timer);
+	clear_bit(NCI_DATA_EXCHANGE_TO, &ndev->flags);
+
+	/* Mark the exchange as done before calling the callback.
+	 * The callback (e.g. rawsock_data_exchange_complete) may
+	 * want to immediately queue another data exchange.
+	 */
+	clear_bit(NCI_DATA_EXCHANGE, &ndev->flags);
+
+	if (cb) {
+		/* forward skb to nfc core */
+		cb(cb_context, skb, err);
+	} else if (skb) {
+		pr_err("no rx callback, dropping rx data...\n");
+
+		/* no waiting callback, free skb */
+		kfree_skb(skb);
+	}
+}
+
+/* ----------------- NCI TX Data ----------------- */
+
+static inline void nci_push_data_hdr(struct nci_dev *ndev,
+				     __u8 conn_id,
+				     struct sk_buff *skb,
+				     __u8 pbf)
+{
+	struct nci_data_hdr *hdr;
+	int plen = skb->len;
+
+	hdr = skb_push(skb, NCI_DATA_HDR_SIZE);
+	hdr->conn_id = conn_id;
+	hdr->rfu = 0;
+	hdr->plen = plen;
+
+	nci_mt_set((__u8 *)hdr, NCI_MT_DATA_PKT);
+	nci_pbf_set((__u8 *)hdr, pbf);
+}
+
+int nci_conn_max_data_pkt_payload_size(struct nci_dev *ndev, __u8 conn_id)
+{
+	const struct nci_conn_info *conn_info;
+
+	conn_info = nci_get_conn_info_by_conn_id(ndev, conn_id);
+	if (!conn_info)
+		return -EPROTO;
+
+	return conn_info->max_pkt_payload_len;
+}
+EXPORT_SYMBOL(nci_conn_max_data_pkt_payload_size);
+
+static int nci_queue_tx_data_frags(struct nci_dev *ndev,
+				   __u8 conn_id,
+				   struct sk_buff *skb) {
+	const struct nci_conn_info *conn_info;
+	int total_len = skb->len;
+	const unsigned char *data = skb->data;
+	unsigned long flags;
+	struct sk_buff_head frags_q;
+	struct sk_buff *skb_frag;
+	int frag_len;
+	int rc = 0;
+
+	pr_debug("conn_id 0x%x, total_len %d\n", conn_id, total_len);
+
+	conn_info = nci_get_conn_info_by_conn_id(ndev, conn_id);
+	if (!conn_info) {
+		rc = -EPROTO;
+		goto exit;
+	}
+
+	__skb_queue_head_init(&frags_q);
+
+	while (total_len) {
+		frag_len =
+			min_t(int, total_len, conn_info->max_pkt_payload_len);
+
+		skb_frag = nci_skb_alloc(ndev,
+					 (NCI_DATA_HDR_SIZE + frag_len),
+					 GFP_ATOMIC);
+		if (skb_frag == NULL) {
+			rc = -ENOMEM;
+			goto free_exit;
+		}
+		skb_reserve(skb_frag, NCI_DATA_HDR_SIZE);
+
+		/* first, copy the data */
+		skb_put_data(skb_frag, data, frag_len);
+
+		/* second, set the header */
+		nci_push_data_hdr(ndev, conn_id, skb_frag,
+				  ((total_len == frag_len) ?
+				   (NCI_PBF_LAST) : (NCI_PBF_CONT)));
+
+		__skb_queue_tail(&frags_q, skb_frag);
+
+		data += frag_len;
+		total_len -= frag_len;
+
+		pr_debug("frag_len %d, remaining total_len %d\n",
+			 frag_len, total_len);
+	}
+
+	/* queue all fragments atomically */
+	spin_lock_irqsave(&ndev->tx_q.lock, flags);
+
+	while ((skb_frag = __skb_dequeue(&frags_q)) != NULL)
+		__skb_queue_tail(&ndev->tx_q, skb_frag);
+
+	spin_unlock_irqrestore(&ndev->tx_q.lock, flags);
+
+	/* free the original skb */
+	kfree_skb(skb);
+
+	goto exit;
+
+free_exit:
+	while ((skb_frag = __skb_dequeue(&frags_q)) != NULL)
+		kfree_skb(skb_frag);
+
+exit:
+	return rc;
+}
+
+/* Send NCI data */
+int nci_send_data(struct nci_dev *ndev, __u8 conn_id, struct sk_buff *skb)
+{
+	const struct nci_conn_info *conn_info;
+	int rc = 0;
+
+	pr_debug("conn_id 0x%x, plen %d\n", conn_id, skb->len);
+
+	conn_info = nci_get_conn_info_by_conn_id(ndev, conn_id);
+	if (!conn_info) {
+		rc = -EPROTO;
+		goto free_exit;
+	}
+
+	/* check if the packet need to be fragmented */
+	if (skb->len <= conn_info->max_pkt_payload_len) {
+		/* no need to fragment packet */
+		nci_push_data_hdr(ndev, conn_id, skb, NCI_PBF_LAST);
+
+		skb_queue_tail(&ndev->tx_q, skb);
+	} else {
+		/* fragment packet and queue the fragments */
+		rc = nci_queue_tx_data_frags(ndev, conn_id, skb);
+		if (rc) {
+			pr_err("failed to fragment tx data packet\n");
+			goto free_exit;
+		}
+	}
+
+	ndev->cur_conn_id = conn_id;
+	queue_work(ndev->tx_wq, &ndev->tx_work);
+
+	goto exit;
+
+free_exit:
+	kfree_skb(skb);
+
+exit:
+	return rc;
+}
+EXPORT_SYMBOL(nci_send_data);
+
+/* ----------------- NCI RX Data ----------------- */
+
+static void nci_add_rx_data_frag(struct nci_dev *ndev,
+				 struct sk_buff *skb,
+				 __u8 pbf, __u8 conn_id, __u8 status)
+{
+	int reassembly_len;
+	int err = 0;
+
+	if (status) {
+		err = status;
+		goto exit;
+	}
+
+	if (ndev->rx_data_reassembly) {
+		reassembly_len = ndev->rx_data_reassembly->len;
+
+		/* first, make enough room for the already accumulated data */
+		if (skb_cow_head(skb, reassembly_len)) {
+			pr_err("error adding room for accumulated rx data\n");
+
+			kfree_skb(skb);
+			skb = NULL;
+
+			kfree_skb(ndev->rx_data_reassembly);
+			ndev->rx_data_reassembly = NULL;
+
+			err = -ENOMEM;
+			goto exit;
+		}
+
+		/* second, combine the two fragments */
+		memcpy(skb_push(skb, reassembly_len),
+		       ndev->rx_data_reassembly->data,
+		       reassembly_len);
+
+		/* third, free old reassembly */
+		kfree_skb(ndev->rx_data_reassembly);
+		ndev->rx_data_reassembly = NULL;
+	}
+
+	if (pbf == NCI_PBF_CONT) {
+		/* need to wait for next fragment, store skb and exit */
+		ndev->rx_data_reassembly = skb;
+		return;
+	}
+
+exit:
+	if (ndev->nfc_dev->rf_mode == NFC_RF_TARGET) {
+		/* Data received in Target mode, forward to nfc core */
+		err = nfc_tm_data_received(ndev->nfc_dev, skb);
+		if (err)
+			pr_err("unable to handle received data\n");
+	} else {
+		nci_data_exchange_complete(ndev, skb, conn_id, err);
+	}
+}
+
+/* Rx Data packet */
+void nci_rx_data_packet(struct nci_dev *ndev, struct sk_buff *skb)
+{
+	__u8 pbf = nci_pbf(skb->data);
+	__u8 status = 0;
+	__u8 conn_id = nci_conn_id(skb->data);
+	const struct nci_conn_info *conn_info;
+
+	pr_debug("len %d\n", skb->len);
+
+	pr_debug("NCI RX: MT=data, PBF=%d, conn_id=%d, plen=%d\n",
+		 nci_pbf(skb->data),
+		 nci_conn_id(skb->data),
+		 nci_plen(skb->data));
+
+	conn_info = nci_get_conn_info_by_conn_id(ndev, nci_conn_id(skb->data));
+	if (!conn_info) {
+		kfree_skb(skb);
+		return;
+	}
+
+	/* strip the nci data header */
+	skb_pull(skb, NCI_DATA_HDR_SIZE);
+
+	if (ndev->target_active_prot == NFC_PROTO_MIFARE ||
+	    ndev->target_active_prot == NFC_PROTO_JEWEL ||
+	    ndev->target_active_prot == NFC_PROTO_FELICA ||
+	    ndev->target_active_prot == NFC_PROTO_ISO15693) {
+		/* frame I/F => remove the status byte */
+		pr_debug("frame I/F => remove the status byte\n");
+		status = skb->data[skb->len - 1];
+		skb_trim(skb, (skb->len - 1));
+	}
+
+	nci_add_rx_data_frag(ndev, skb, pbf, conn_id, nci_to_errno(status));
+}