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, 230 insertions, 0 deletions

diff --git a/drivers/bluetooth/btqcomsmd.c b/drivers/bluetooth/btqcomsmd.c
new file mode 100644
index 000000000..d2e13fcb6
--- /dev/null
+++ b/drivers/bluetooth/btqcomsmd.c
@@ -0,0 +1,230 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2016, Linaro Ltd.
+ * Copyright (c) 2015, Sony Mobile Communications Inc.
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/rpmsg.h>
+#include <linux/of.h>
+
+#include <linux/soc/qcom/wcnss_ctrl.h>
+#include <linux/platform_device.h>
+
+#include <net/bluetooth/bluetooth.h>
+#include <net/bluetooth/hci_core.h>
+
+#include "btqca.h"
+
+struct btqcomsmd {
+	struct hci_dev *hdev;
+
+	struct rpmsg_endpoint *acl_channel;
+	struct rpmsg_endpoint *cmd_channel;
+};
+
+static int btqcomsmd_recv(struct hci_dev *hdev, unsigned int type,
+			   const void *data, size_t count)
+{
+	struct sk_buff *skb;
+
+	/* Use GFP_ATOMIC as we're in IRQ context */
+	skb = bt_skb_alloc(count, GFP_ATOMIC);
+	if (!skb) {
+		hdev->stat.err_rx++;
+		return -ENOMEM;
+	}
+
+	hci_skb_pkt_type(skb) = type;
+	skb_put_data(skb, data, count);
+
+	return hci_recv_frame(hdev, skb);
+}
+
+static int btqcomsmd_acl_callback(struct rpmsg_device *rpdev, void *data,
+				  int count, void *priv, u32 addr)
+{
+	struct btqcomsmd *btq = priv;
+
+	btq->hdev->stat.byte_rx += count;
+	return btqcomsmd_recv(btq->hdev, HCI_ACLDATA_PKT, data, count);
+}
+
+static int btqcomsmd_cmd_callback(struct rpmsg_device *rpdev, void *data,
+				  int count, void *priv, u32 addr)
+{
+	struct btqcomsmd *btq = priv;
+
+	btq->hdev->stat.byte_rx += count;
+	return btqcomsmd_recv(btq->hdev, HCI_EVENT_PKT, data, count);
+}
+
+static int btqcomsmd_send(struct hci_dev *hdev, struct sk_buff *skb)
+{
+	struct btqcomsmd *btq = hci_get_drvdata(hdev);
+	int ret;
+
+	switch (hci_skb_pkt_type(skb)) {
+	case HCI_ACLDATA_PKT:
+		ret = rpmsg_send(btq->acl_channel, skb->data, skb->len);
+		if (ret) {
+			hdev->stat.err_tx++;
+			break;
+		}
+		hdev->stat.acl_tx++;
+		hdev->stat.byte_tx += skb->len;
+		break;
+	case HCI_COMMAND_PKT:
+		ret = rpmsg_send(btq->cmd_channel, skb->data, skb->len);
+		if (ret) {
+			hdev->stat.err_tx++;
+			break;
+		}
+		hdev->stat.cmd_tx++;
+		hdev->stat.byte_tx += skb->len;
+		break;
+	default:
+		ret = -EILSEQ;
+		break;
+	}
+
+	if (!ret)
+		kfree_skb(skb);
+
+	return ret;
+}
+
+static int btqcomsmd_open(struct hci_dev *hdev)
+{
+	return 0;
+}
+
+static int btqcomsmd_close(struct hci_dev *hdev)
+{
+	return 0;
+}
+
+static int btqcomsmd_setup(struct hci_dev *hdev)
+{
+	struct sk_buff *skb;
+
+	skb = __hci_cmd_sync(hdev, HCI_OP_RESET, 0, NULL, HCI_INIT_TIMEOUT);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+	kfree_skb(skb);
+
+	/* Devices do not have persistent storage for BD address. Retrieve
+	 * it from the firmware node property.
+	 */
+	hci_set_quirk(hdev, HCI_QUIRK_USE_BDADDR_PROPERTY);
+
+	return 0;
+}
+
+static int btqcomsmd_set_bdaddr(struct hci_dev *hdev, const bdaddr_t *bdaddr)
+{
+	int ret;
+
+	ret = qca_set_bdaddr_rome(hdev, bdaddr);
+	if (ret)
+		return ret;
+
+	/* The firmware stops responding for a while after setting the bdaddr,
+	 * causing timeouts for subsequent commands. Sleep a bit to avoid this.
+	 */
+	usleep_range(1000, 10000);
+	return 0;
+}
+
+static int btqcomsmd_probe(struct platform_device *pdev)
+{
+	struct btqcomsmd *btq;
+	struct hci_dev *hdev;
+	void *wcnss;
+	int ret;
+
+	btq = devm_kzalloc(&pdev->dev, sizeof(*btq), GFP_KERNEL);
+	if (!btq)
+		return -ENOMEM;
+
+	wcnss = dev_get_drvdata(pdev->dev.parent);
+
+	btq->acl_channel = qcom_wcnss_open_channel(wcnss, "APPS_RIVA_BT_ACL",
+						   btqcomsmd_acl_callback, btq);
+	if (IS_ERR(btq->acl_channel))
+		return PTR_ERR(btq->acl_channel);
+
+	btq->cmd_channel = qcom_wcnss_open_channel(wcnss, "APPS_RIVA_BT_CMD",
+						   btqcomsmd_cmd_callback, btq);
+	if (IS_ERR(btq->cmd_channel)) {
+		ret = PTR_ERR(btq->cmd_channel);
+		goto destroy_acl_channel;
+	}
+
+	hdev = hci_alloc_dev();
+	if (!hdev) {
+		ret = -ENOMEM;
+		goto destroy_cmd_channel;
+	}
+
+	hci_set_drvdata(hdev, btq);
+	btq->hdev = hdev;
+	SET_HCIDEV_DEV(hdev, &pdev->dev);
+
+	hdev->bus = HCI_SMD;
+	hdev->open = btqcomsmd_open;
+	hdev->close = btqcomsmd_close;
+	hdev->send = btqcomsmd_send;
+	hdev->setup = btqcomsmd_setup;
+	hdev->set_bdaddr = btqcomsmd_set_bdaddr;
+
+	ret = hci_register_dev(hdev);
+	if (ret < 0)
+		goto hci_free_dev;
+
+	platform_set_drvdata(pdev, btq);
+
+	return 0;
+
+hci_free_dev:
+	hci_free_dev(hdev);
+destroy_cmd_channel:
+	rpmsg_destroy_ept(btq->cmd_channel);
+destroy_acl_channel:
+	rpmsg_destroy_ept(btq->acl_channel);
+
+	return ret;
+}
+
+static void btqcomsmd_remove(struct platform_device *pdev)
+{
+	struct btqcomsmd *btq = platform_get_drvdata(pdev);
+
+	hci_unregister_dev(btq->hdev);
+	hci_free_dev(btq->hdev);
+
+	rpmsg_destroy_ept(btq->cmd_channel);
+	rpmsg_destroy_ept(btq->acl_channel);
+}
+
+static const struct of_device_id btqcomsmd_of_match[] = {
+	{ .compatible = "qcom,wcnss-bt", },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, btqcomsmd_of_match);
+
+static struct platform_driver btqcomsmd_driver = {
+	.probe = btqcomsmd_probe,
+	.remove = btqcomsmd_remove,
+	.driver  = {
+		.name  = "btqcomsmd",
+		.of_match_table = btqcomsmd_of_match,
+	},
+};
+
+module_platform_driver(btqcomsmd_driver);
+
+MODULE_AUTHOR("Bjorn Andersson <bjorn.andersson@sonymobile.com>");
+MODULE_DESCRIPTION("Qualcomm SMD HCI driver");
+MODULE_LICENSE("GPL v2");