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, 185 insertions, 0 deletions

diff --git a/drivers/bluetooth/btrsi.c b/drivers/bluetooth/btrsi.c
new file mode 100644
index 000000000..59ad0b9b1
--- /dev/null
+++ b/drivers/bluetooth/btrsi.c
@@ -0,0 +1,185 @@
+// SPDX-License-Identifier: ISC
+/*
+ * Copyright (c) 2017 Redpine Signals Inc.
+ *
+ */
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <net/bluetooth/bluetooth.h>
+#include <net/bluetooth/hci_core.h>
+#include <linux/unaligned.h>
+#include <net/rsi_91x.h>
+
+#define RSI_DMA_ALIGN	8
+#define RSI_FRAME_DESC_SIZE	16
+#define RSI_HEADROOM_FOR_BT_HAL	(RSI_FRAME_DESC_SIZE + RSI_DMA_ALIGN)
+
+struct rsi_hci_adapter {
+	void *priv;
+	struct rsi_proto_ops *proto_ops;
+	struct hci_dev *hdev;
+};
+
+static int rsi_hci_open(struct hci_dev *hdev)
+{
+	return 0;
+}
+
+static int rsi_hci_close(struct hci_dev *hdev)
+{
+	return 0;
+}
+
+static int rsi_hci_flush(struct hci_dev *hdev)
+{
+	return 0;
+}
+
+static int rsi_hci_send_pkt(struct hci_dev *hdev, struct sk_buff *skb)
+{
+	struct rsi_hci_adapter *h_adapter = hci_get_drvdata(hdev);
+	struct sk_buff *new_skb = NULL;
+
+	switch (hci_skb_pkt_type(skb)) {
+	case HCI_COMMAND_PKT:
+		hdev->stat.cmd_tx++;
+		break;
+	case HCI_ACLDATA_PKT:
+		hdev->stat.acl_tx++;
+		break;
+	case HCI_SCODATA_PKT:
+		hdev->stat.sco_tx++;
+		break;
+	}
+
+	if (skb_headroom(skb) < RSI_HEADROOM_FOR_BT_HAL) {
+		/* Insufficient skb headroom - allocate a new skb */
+		new_skb = skb_realloc_headroom(skb, RSI_HEADROOM_FOR_BT_HAL);
+		if (unlikely(!new_skb))
+			return -ENOMEM;
+		bt_cb(new_skb)->pkt_type = hci_skb_pkt_type(skb);
+		kfree_skb(skb);
+		skb = new_skb;
+		if (!IS_ALIGNED((unsigned long)skb->data, RSI_DMA_ALIGN)) {
+			u8 *skb_data = skb->data;
+			int skb_len = skb->len;
+
+			skb_push(skb, RSI_DMA_ALIGN);
+			skb_pull(skb, PTR_ALIGN(skb->data,
+						RSI_DMA_ALIGN) - skb->data);
+			memmove(skb->data, skb_data, skb_len);
+			skb_trim(skb, skb_len);
+		}
+	}
+
+	return h_adapter->proto_ops->coex_send_pkt(h_adapter->priv, skb,
+						   RSI_BT_Q);
+}
+
+static int rsi_hci_recv_pkt(void *priv, const u8 *pkt)
+{
+	struct rsi_hci_adapter *h_adapter = priv;
+	struct hci_dev *hdev = h_adapter->hdev;
+	struct sk_buff *skb;
+	int pkt_len = get_unaligned_le16(pkt) & 0x0fff;
+
+	skb = dev_alloc_skb(pkt_len);
+	if (!skb)
+		return -ENOMEM;
+
+	memcpy(skb->data, pkt + RSI_FRAME_DESC_SIZE, pkt_len);
+	skb_put(skb, pkt_len);
+	h_adapter->hdev->stat.byte_rx += skb->len;
+
+	hci_skb_pkt_type(skb) = pkt[14];
+
+	return hci_recv_frame(hdev, skb);
+}
+
+static int rsi_hci_attach(void *priv, struct rsi_proto_ops *ops)
+{
+	struct rsi_hci_adapter *h_adapter = NULL;
+	struct hci_dev *hdev;
+	int err = 0;
+
+	h_adapter = kzalloc_obj(*h_adapter);
+	if (!h_adapter)
+		return -ENOMEM;
+
+	h_adapter->priv = priv;
+	ops->set_bt_context(priv, h_adapter);
+	h_adapter->proto_ops = ops;
+
+	hdev = hci_alloc_dev();
+	if (!hdev) {
+		BT_ERR("Failed to alloc HCI device");
+		goto err;
+	}
+
+	h_adapter->hdev = hdev;
+
+	if (ops->get_host_intf(priv) == RSI_HOST_INTF_SDIO)
+		hdev->bus = HCI_SDIO;
+	else
+		hdev->bus = HCI_USB;
+
+	hci_set_drvdata(hdev, h_adapter);
+	hdev->open = rsi_hci_open;
+	hdev->close = rsi_hci_close;
+	hdev->flush = rsi_hci_flush;
+	hdev->send = rsi_hci_send_pkt;
+
+	err = hci_register_dev(hdev);
+	if (err < 0) {
+		BT_ERR("HCI registration failed with errcode %d", err);
+		hci_free_dev(hdev);
+		goto err;
+	}
+
+	return 0;
+err:
+	h_adapter->hdev = NULL;
+	kfree(h_adapter);
+	return -EINVAL;
+}
+
+static void rsi_hci_detach(void *priv)
+{
+	struct rsi_hci_adapter *h_adapter = priv;
+	struct hci_dev *hdev;
+
+	if (!h_adapter)
+		return;
+
+	hdev = h_adapter->hdev;
+	if (hdev) {
+		hci_unregister_dev(hdev);
+		hci_free_dev(hdev);
+		h_adapter->hdev = NULL;
+	}
+
+	kfree(h_adapter);
+}
+
+const struct rsi_mod_ops rsi_bt_ops = {
+	.attach	= rsi_hci_attach,
+	.detach	= rsi_hci_detach,
+	.recv_pkt = rsi_hci_recv_pkt,
+};
+EXPORT_SYMBOL(rsi_bt_ops);
+
+static int rsi_91x_bt_module_init(void)
+{
+	return 0;
+}
+
+static void rsi_91x_bt_module_exit(void)
+{
+	return;
+}
+
+module_init(rsi_91x_bt_module_init);
+module_exit(rsi_91x_bt_module_exit);
+MODULE_AUTHOR("Redpine Signals Inc");
+MODULE_DESCRIPTION("RSI BT driver");
+MODULE_LICENSE("Dual BSD/GPL");