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, 396 insertions, 0 deletions

diff --git a/drivers/nfc/mei_phy.c b/drivers/nfc/mei_phy.c
new file mode 100644
index 000000000..0ea28597e
--- /dev/null
+++ b/drivers/nfc/mei_phy.c
@@ -0,0 +1,396 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2013, Intel Corporation.
+ *
+ * MEI Library for mei bus nfc device access
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/nfc.h>
+
+#include "mei_phy.h"
+
+struct mei_nfc_hdr {
+	u8 cmd;
+	u8 status;
+	u16 req_id;
+	u32 reserved;
+	u16 data_size;
+} __packed;
+
+struct mei_nfc_cmd {
+	struct mei_nfc_hdr hdr;
+	u8 sub_command;
+	u8 data[];
+} __packed;
+
+struct mei_nfc_reply {
+	struct mei_nfc_hdr hdr;
+	u8 sub_command;
+	u8 reply_status;
+	u8 data[];
+} __packed;
+
+struct mei_nfc_if_version {
+	u8 radio_version_sw[3];
+	u8 reserved[3];
+	u8 radio_version_hw[3];
+	u8 i2c_addr;
+	u8 fw_ivn;
+	u8 vendor_id;
+	u8 radio_type;
+} __packed;
+
+struct mei_nfc_connect {
+	u8 fw_ivn;
+	u8 vendor_id;
+} __packed;
+
+struct mei_nfc_connect_resp {
+	u8 fw_ivn;
+	u8 vendor_id;
+	u16 me_major;
+	u16 me_minor;
+	u16 me_hotfix;
+	u16 me_build;
+} __packed;
+
+
+#define MEI_NFC_CMD_MAINTENANCE 0x00
+#define MEI_NFC_CMD_HCI_SEND 0x01
+#define MEI_NFC_CMD_HCI_RECV 0x02
+
+#define MEI_NFC_SUBCMD_CONNECT    0x00
+#define MEI_NFC_SUBCMD_IF_VERSION 0x01
+
+#define MEI_NFC_MAX_READ (MEI_NFC_HEADER_SIZE + MEI_NFC_MAX_HCI_PAYLOAD)
+
+#define MEI_DUMP_SKB_IN(info, skb)				\
+do {								\
+	pr_debug("%s:\n", info);				\
+	print_hex_dump_debug("mei in : ", DUMP_PREFIX_OFFSET,	\
+			16, 1, (skb)->data, (skb)->len, false);	\
+} while (0)
+
+#define MEI_DUMP_SKB_OUT(info, skb)				\
+do {								\
+	pr_debug("%s:\n", info);				\
+	print_hex_dump_debug("mei out: ", DUMP_PREFIX_OFFSET,	\
+			16, 1, (skb)->data, (skb)->len, false);	\
+} while (0)
+
+#define MEI_DUMP_NFC_HDR(info, _hdr)                                \
+do {                                                                \
+	pr_debug("%s:\n", info);                                    \
+	pr_debug("cmd=%02d status=%d req_id=%d rsvd=%d size=%d\n",  \
+		 (_hdr)->cmd, (_hdr)->status, (_hdr)->req_id,       \
+		 (_hdr)->reserved, (_hdr)->data_size);              \
+} while (0)
+
+static int mei_nfc_if_version(struct nfc_mei_phy *phy)
+{
+
+	struct mei_nfc_cmd cmd;
+	struct mei_nfc_reply *reply = NULL;
+	struct mei_nfc_if_version *version;
+	size_t if_version_length;
+	int bytes_recv, r;
+
+	memset(&cmd, 0, sizeof(struct mei_nfc_cmd));
+	cmd.hdr.cmd = MEI_NFC_CMD_MAINTENANCE;
+	cmd.hdr.data_size = 1;
+	cmd.sub_command = MEI_NFC_SUBCMD_IF_VERSION;
+
+	MEI_DUMP_NFC_HDR("version", &cmd.hdr);
+	r = mei_cldev_send(phy->cldev, (u8 *)&cmd, sizeof(struct mei_nfc_cmd));
+	if (r < 0) {
+		pr_err("Could not send IF version cmd\n");
+		return r;
+	}
+
+	/* to be sure on the stack we alloc memory */
+	if_version_length = sizeof(struct mei_nfc_reply) +
+		sizeof(struct mei_nfc_if_version);
+
+	reply = kzalloc(if_version_length, GFP_KERNEL);
+	if (!reply)
+		return -ENOMEM;
+
+	bytes_recv = mei_cldev_recv(phy->cldev, (u8 *)reply, if_version_length);
+	if (bytes_recv < 0 || bytes_recv < if_version_length) {
+		pr_err("Could not read IF version\n");
+		r = -EIO;
+		goto err;
+	}
+
+	version = (struct mei_nfc_if_version *)reply->data;
+
+	phy->fw_ivn = version->fw_ivn;
+	phy->vendor_id = version->vendor_id;
+	phy->radio_type = version->radio_type;
+
+err:
+	kfree(reply);
+	return r;
+}
+
+static int mei_nfc_connect(struct nfc_mei_phy *phy)
+{
+	struct mei_nfc_cmd *cmd, *reply;
+	struct mei_nfc_connect *connect;
+	struct mei_nfc_connect_resp *connect_resp;
+	size_t connect_length, connect_resp_length;
+	int bytes_recv, r;
+
+	connect_length = sizeof(struct mei_nfc_cmd) +
+			sizeof(struct mei_nfc_connect);
+
+	connect_resp_length = sizeof(struct mei_nfc_cmd) +
+			sizeof(struct mei_nfc_connect_resp);
+
+	cmd = kzalloc(connect_length, GFP_KERNEL);
+	if (!cmd)
+		return -ENOMEM;
+	connect = (struct mei_nfc_connect *)cmd->data;
+
+	reply = kzalloc(connect_resp_length, GFP_KERNEL);
+	if (!reply) {
+		kfree(cmd);
+		return -ENOMEM;
+	}
+
+	connect_resp = (struct mei_nfc_connect_resp *)reply->data;
+
+	cmd->hdr.cmd = MEI_NFC_CMD_MAINTENANCE;
+	cmd->hdr.data_size = 3;
+	cmd->sub_command = MEI_NFC_SUBCMD_CONNECT;
+	connect->fw_ivn = phy->fw_ivn;
+	connect->vendor_id = phy->vendor_id;
+
+	MEI_DUMP_NFC_HDR("connect request", &cmd->hdr);
+	r = mei_cldev_send(phy->cldev, (u8 *)cmd, connect_length);
+	if (r < 0) {
+		pr_err("Could not send connect cmd %d\n", r);
+		goto err;
+	}
+
+	bytes_recv = mei_cldev_recv(phy->cldev, (u8 *)reply,
+				    connect_resp_length);
+	if (bytes_recv < 0) {
+		r = bytes_recv;
+		pr_err("Could not read connect response %d\n", r);
+		goto err;
+	}
+
+	MEI_DUMP_NFC_HDR("connect reply", &reply->hdr);
+
+	pr_info("IVN 0x%x Vendor ID 0x%x\n",
+		 connect_resp->fw_ivn, connect_resp->vendor_id);
+
+	pr_info("ME FW %d.%d.%d.%d\n",
+		connect_resp->me_major, connect_resp->me_minor,
+		connect_resp->me_hotfix, connect_resp->me_build);
+
+	r = 0;
+
+err:
+	kfree(reply);
+	kfree(cmd);
+
+	return r;
+}
+
+static int mei_nfc_send(struct nfc_mei_phy *phy, const u8 *buf, size_t length)
+{
+	struct mei_nfc_hdr *hdr;
+	u8 *mei_buf;
+	int err;
+
+	err = -ENOMEM;
+	mei_buf = kzalloc(length + MEI_NFC_HEADER_SIZE, GFP_KERNEL);
+	if (!mei_buf)
+		goto out;
+
+	hdr = (struct mei_nfc_hdr *)mei_buf;
+	hdr->cmd = MEI_NFC_CMD_HCI_SEND;
+	hdr->status = 0;
+	hdr->req_id = phy->req_id;
+	hdr->reserved = 0;
+	hdr->data_size = length;
+
+	MEI_DUMP_NFC_HDR("send", hdr);
+
+	memcpy(mei_buf + MEI_NFC_HEADER_SIZE, buf, length);
+	err = mei_cldev_send(phy->cldev, mei_buf, length + MEI_NFC_HEADER_SIZE);
+	if (err < 0)
+		goto out;
+
+	if (!wait_event_interruptible_timeout(phy->send_wq,
+				phy->recv_req_id == phy->req_id, HZ)) {
+		pr_err("NFC MEI command timeout\n");
+		err = -ETIME;
+	} else {
+		phy->req_id++;
+	}
+out:
+	kfree(mei_buf);
+	return err;
+}
+
+/*
+ * Writing a frame must not return the number of written bytes.
+ * It must return either zero for success, or <0 for error.
+ * In addition, it must not alter the skb
+ */
+static int nfc_mei_phy_write(void *phy_id, struct sk_buff *skb)
+{
+	struct nfc_mei_phy *phy = phy_id;
+	int r;
+
+	MEI_DUMP_SKB_OUT("mei frame sent", skb);
+
+	r = mei_nfc_send(phy, skb->data, skb->len);
+	if (r > 0)
+		r = 0;
+
+	return r;
+}
+
+static int mei_nfc_recv(struct nfc_mei_phy *phy, u8 *buf, size_t length)
+{
+	struct mei_nfc_hdr *hdr;
+	int received_length;
+
+	received_length = mei_cldev_recv(phy->cldev, buf, length);
+	if (received_length < 0)
+		return received_length;
+
+	hdr = (struct mei_nfc_hdr *) buf;
+
+	MEI_DUMP_NFC_HDR("receive", hdr);
+	if (hdr->cmd == MEI_NFC_CMD_HCI_SEND) {
+		phy->recv_req_id = hdr->req_id;
+		wake_up(&phy->send_wq);
+
+		return 0;
+	}
+
+	return received_length;
+}
+
+
+static void nfc_mei_rx_cb(struct mei_cl_device *cldev)
+{
+	struct nfc_mei_phy *phy = mei_cldev_get_drvdata(cldev);
+	struct sk_buff *skb;
+	int reply_size;
+
+	if (!phy)
+		return;
+
+	if (phy->hard_fault != 0)
+		return;
+
+	skb = alloc_skb(MEI_NFC_MAX_READ, GFP_KERNEL);
+	if (!skb)
+		return;
+
+	reply_size = mei_nfc_recv(phy, skb->data, MEI_NFC_MAX_READ);
+	if (reply_size < MEI_NFC_HEADER_SIZE) {
+		kfree_skb(skb);
+		return;
+	}
+
+	skb_put(skb, reply_size);
+	skb_pull(skb, MEI_NFC_HEADER_SIZE);
+
+	MEI_DUMP_SKB_IN("mei frame read", skb);
+
+	nfc_hci_recv_frame(phy->hdev, skb);
+}
+
+static int nfc_mei_phy_enable(void *phy_id)
+{
+	int r;
+	struct nfc_mei_phy *phy = phy_id;
+
+	if (phy->powered == 1)
+		return 0;
+
+	r = mei_cldev_enable(phy->cldev);
+	if (r < 0) {
+		pr_err("Could not enable device %d\n", r);
+		return r;
+	}
+
+	r = mei_nfc_if_version(phy);
+	if (r < 0) {
+		pr_err("Could not enable device %d\n", r);
+		goto err;
+	}
+
+	r = mei_nfc_connect(phy);
+	if (r < 0) {
+		pr_err("Could not connect to device %d\n", r);
+		goto err;
+	}
+
+	r = mei_cldev_register_rx_cb(phy->cldev, nfc_mei_rx_cb);
+	if (r) {
+		pr_err("Event cb registration failed %d\n", r);
+		goto err;
+	}
+
+	phy->powered = 1;
+
+	return 0;
+
+err:
+	phy->powered = 0;
+	mei_cldev_disable(phy->cldev);
+	return r;
+}
+
+static void nfc_mei_phy_disable(void *phy_id)
+{
+	struct nfc_mei_phy *phy = phy_id;
+
+	mei_cldev_disable(phy->cldev);
+
+	phy->powered = 0;
+}
+
+const struct nfc_phy_ops mei_phy_ops = {
+	.write = nfc_mei_phy_write,
+	.enable = nfc_mei_phy_enable,
+	.disable = nfc_mei_phy_disable,
+};
+EXPORT_SYMBOL_GPL(mei_phy_ops);
+
+struct nfc_mei_phy *nfc_mei_phy_alloc(struct mei_cl_device *cldev)
+{
+	struct nfc_mei_phy *phy;
+
+	phy = kzalloc_obj(struct nfc_mei_phy);
+	if (!phy)
+		return NULL;
+
+	phy->cldev = cldev;
+	init_waitqueue_head(&phy->send_wq);
+	mei_cldev_set_drvdata(cldev, phy);
+
+	return phy;
+}
+EXPORT_SYMBOL_GPL(nfc_mei_phy_alloc);
+
+void nfc_mei_phy_free(struct nfc_mei_phy *phy)
+{
+	mei_cldev_disable(phy->cldev);
+	kfree(phy);
+}
+EXPORT_SYMBOL_GPL(nfc_mei_phy_free);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("mei bus NFC device interface");