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, 495 insertions, 0 deletions

diff --git a/drivers/nfc/nfcsim.c b/drivers/nfc/nfcsim.c
new file mode 100644
index 000000000..f8e5c4da3
--- /dev/null
+++ b/drivers/nfc/nfcsim.c
@@ -0,0 +1,495 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * NFC hardware simulation driver
+ * Copyright (c) 2013, Intel Corporation.
+ */
+
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/ctype.h>
+#include <linux/debugfs.h>
+#include <linux/nfc.h>
+#include <net/nfc/nfc.h>
+#include <net/nfc/digital.h>
+
+#define NFCSIM_ERR(d, fmt, args...) nfc_err(&d->nfc_digital_dev->nfc_dev->dev, \
+					    "%s: " fmt, __func__, ## args)
+
+#define NFCSIM_DBG(d, fmt, args...) dev_dbg(&d->nfc_digital_dev->nfc_dev->dev, \
+					    "%s: " fmt, __func__, ## args)
+
+#define NFCSIM_VERSION "0.2"
+
+#define NFCSIM_MODE_NONE	0
+#define NFCSIM_MODE_INITIATOR	1
+#define NFCSIM_MODE_TARGET	2
+
+#define NFCSIM_CAPABILITIES (NFC_DIGITAL_DRV_CAPS_IN_CRC   | \
+			     NFC_DIGITAL_DRV_CAPS_TG_CRC)
+
+struct nfcsim {
+	struct nfc_digital_dev *nfc_digital_dev;
+
+	struct work_struct recv_work;
+	struct delayed_work send_work;
+
+	struct nfcsim_link *link_in;
+	struct nfcsim_link *link_out;
+
+	bool up;
+	u8 mode;
+	u8 rf_tech;
+
+	u16 recv_timeout;
+
+	nfc_digital_cmd_complete_t cb;
+	void *arg;
+
+	u8 dropframe;
+};
+
+struct nfcsim_link {
+	struct mutex lock;
+
+	u8 rf_tech;
+	u8 mode;
+
+	u8 shutdown;
+
+	struct sk_buff *skb;
+	wait_queue_head_t recv_wait;
+	u8 cond;
+};
+
+static struct nfcsim_link *nfcsim_link_new(void)
+{
+	struct nfcsim_link *link;
+
+	link = kzalloc_obj(struct nfcsim_link);
+	if (!link)
+		return NULL;
+
+	mutex_init(&link->lock);
+	init_waitqueue_head(&link->recv_wait);
+
+	return link;
+}
+
+static void nfcsim_link_free(struct nfcsim_link *link)
+{
+	dev_kfree_skb(link->skb);
+	kfree(link);
+}
+
+static void nfcsim_link_recv_wake(struct nfcsim_link *link)
+{
+	link->cond = 1;
+	wake_up_interruptible(&link->recv_wait);
+}
+
+static void nfcsim_link_set_skb(struct nfcsim_link *link, struct sk_buff *skb,
+				u8 rf_tech, u8 mode)
+{
+	mutex_lock(&link->lock);
+
+	dev_kfree_skb(link->skb);
+	link->skb = skb;
+	link->rf_tech = rf_tech;
+	link->mode = mode;
+
+	mutex_unlock(&link->lock);
+}
+
+static void nfcsim_link_recv_cancel(struct nfcsim_link *link)
+{
+	mutex_lock(&link->lock);
+
+	link->mode = NFCSIM_MODE_NONE;
+
+	mutex_unlock(&link->lock);
+
+	nfcsim_link_recv_wake(link);
+}
+
+static void nfcsim_link_shutdown(struct nfcsim_link *link)
+{
+	mutex_lock(&link->lock);
+
+	link->shutdown = 1;
+	link->mode = NFCSIM_MODE_NONE;
+
+	mutex_unlock(&link->lock);
+
+	nfcsim_link_recv_wake(link);
+}
+
+static struct sk_buff *nfcsim_link_recv_skb(struct nfcsim_link *link,
+					    int timeout, u8 rf_tech, u8 mode)
+{
+	int rc;
+	struct sk_buff *skb;
+
+	rc = wait_event_interruptible_timeout(link->recv_wait,
+					      link->cond,
+					      msecs_to_jiffies(timeout));
+
+	mutex_lock(&link->lock);
+
+	skb = link->skb;
+	link->skb = NULL;
+
+	if (!rc) {
+		rc = -ETIMEDOUT;
+		goto done;
+	}
+
+	if (!skb || link->rf_tech != rf_tech || link->mode == mode) {
+		rc = -EINVAL;
+		goto done;
+	}
+
+	if (link->shutdown) {
+		rc = -ENODEV;
+		goto done;
+	}
+
+done:
+	mutex_unlock(&link->lock);
+
+	if (rc < 0) {
+		dev_kfree_skb(skb);
+		skb = ERR_PTR(rc);
+	}
+
+	link->cond = 0;
+
+	return skb;
+}
+
+static void nfcsim_send_wq(struct work_struct *work)
+{
+	struct nfcsim *dev = container_of(work, struct nfcsim, send_work.work);
+
+	/*
+	 * To effectively send data, the device just wake up its link_out which
+	 * is the link_in of the peer device. The exchanged skb has already been
+	 * stored in the dev->link_out through nfcsim_link_set_skb().
+	 */
+	nfcsim_link_recv_wake(dev->link_out);
+}
+
+static void nfcsim_recv_wq(struct work_struct *work)
+{
+	struct nfcsim *dev = container_of(work, struct nfcsim, recv_work);
+	struct sk_buff *skb;
+
+	skb = nfcsim_link_recv_skb(dev->link_in, dev->recv_timeout,
+				   dev->rf_tech, dev->mode);
+
+	if (!dev->up) {
+		NFCSIM_ERR(dev, "Device is down\n");
+
+		if (!IS_ERR(skb))
+			dev_kfree_skb(skb);
+		return;
+	}
+
+	dev->cb(dev->nfc_digital_dev, dev->arg, skb);
+}
+
+static int nfcsim_send(struct nfc_digital_dev *ddev, struct sk_buff *skb,
+		       u16 timeout, nfc_digital_cmd_complete_t cb, void *arg)
+{
+	struct nfcsim *dev = nfc_digital_get_drvdata(ddev);
+	u8 delay;
+
+	if (!dev->up) {
+		NFCSIM_ERR(dev, "Device is down\n");
+		return -ENODEV;
+	}
+
+	dev->recv_timeout = timeout;
+	dev->cb = cb;
+	dev->arg = arg;
+
+	schedule_work(&dev->recv_work);
+
+	if (dev->dropframe) {
+		NFCSIM_DBG(dev, "dropping frame (out of %d)\n", dev->dropframe);
+		dev_kfree_skb(skb);
+		dev->dropframe--;
+
+		return 0;
+	}
+
+	if (skb) {
+		nfcsim_link_set_skb(dev->link_out, skb, dev->rf_tech,
+				    dev->mode);
+
+		/* Add random delay (between 3 and 10 ms) before sending data */
+		get_random_bytes(&delay, 1);
+		delay = 3 + (delay & 0x07);
+
+		schedule_delayed_work(&dev->send_work, msecs_to_jiffies(delay));
+	}
+
+	return 0;
+}
+
+static void nfcsim_abort_cmd(struct nfc_digital_dev *ddev)
+{
+	const struct nfcsim *dev = nfc_digital_get_drvdata(ddev);
+
+	nfcsim_link_recv_cancel(dev->link_in);
+}
+
+static int nfcsim_switch_rf(struct nfc_digital_dev *ddev, bool on)
+{
+	struct nfcsim *dev = nfc_digital_get_drvdata(ddev);
+
+	dev->up = on;
+
+	return 0;
+}
+
+static int nfcsim_in_configure_hw(struct nfc_digital_dev *ddev,
+					  int type, int param)
+{
+	struct nfcsim *dev = nfc_digital_get_drvdata(ddev);
+
+	switch (type) {
+	case NFC_DIGITAL_CONFIG_RF_TECH:
+		dev->up = true;
+		dev->mode = NFCSIM_MODE_INITIATOR;
+		dev->rf_tech = param;
+		break;
+
+	case NFC_DIGITAL_CONFIG_FRAMING:
+		break;
+
+	default:
+		NFCSIM_ERR(dev, "Invalid configuration type: %d\n", type);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int nfcsim_in_send_cmd(struct nfc_digital_dev *ddev,
+			       struct sk_buff *skb, u16 timeout,
+			       nfc_digital_cmd_complete_t cb, void *arg)
+{
+	return nfcsim_send(ddev, skb, timeout, cb, arg);
+}
+
+static int nfcsim_tg_configure_hw(struct nfc_digital_dev *ddev,
+					  int type, int param)
+{
+	struct nfcsim *dev = nfc_digital_get_drvdata(ddev);
+
+	switch (type) {
+	case NFC_DIGITAL_CONFIG_RF_TECH:
+		dev->up = true;
+		dev->mode = NFCSIM_MODE_TARGET;
+		dev->rf_tech = param;
+		break;
+
+	case NFC_DIGITAL_CONFIG_FRAMING:
+		break;
+
+	default:
+		NFCSIM_ERR(dev, "Invalid configuration type: %d\n", type);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int nfcsim_tg_send_cmd(struct nfc_digital_dev *ddev,
+			       struct sk_buff *skb, u16 timeout,
+			       nfc_digital_cmd_complete_t cb, void *arg)
+{
+	return nfcsim_send(ddev, skb, timeout, cb, arg);
+}
+
+static int nfcsim_tg_listen(struct nfc_digital_dev *ddev, u16 timeout,
+			    nfc_digital_cmd_complete_t cb, void *arg)
+{
+	return nfcsim_send(ddev, NULL, timeout, cb, arg);
+}
+
+static const struct nfc_digital_ops nfcsim_digital_ops = {
+	.in_configure_hw = nfcsim_in_configure_hw,
+	.in_send_cmd = nfcsim_in_send_cmd,
+
+	.tg_listen = nfcsim_tg_listen,
+	.tg_configure_hw = nfcsim_tg_configure_hw,
+	.tg_send_cmd = nfcsim_tg_send_cmd,
+
+	.abort_cmd = nfcsim_abort_cmd,
+	.switch_rf = nfcsim_switch_rf,
+};
+
+static struct dentry *nfcsim_debugfs_root;
+
+static void nfcsim_debugfs_init(void)
+{
+	nfcsim_debugfs_root = debugfs_create_dir("nfcsim", NULL);
+}
+
+static void nfcsim_debugfs_remove(void)
+{
+	debugfs_remove_recursive(nfcsim_debugfs_root);
+}
+
+static void nfcsim_debugfs_init_dev(struct nfcsim *dev)
+{
+	struct dentry *dev_dir;
+	char devname[5]; /* nfcX\0 */
+	u32 idx;
+	int n;
+
+	if (!nfcsim_debugfs_root) {
+		NFCSIM_ERR(dev, "nfcsim debugfs not initialized\n");
+		return;
+	}
+
+	idx = dev->nfc_digital_dev->nfc_dev->idx;
+	n = snprintf(devname, sizeof(devname), "nfc%d", idx);
+	if (n >= sizeof(devname)) {
+		NFCSIM_ERR(dev, "Could not compute dev name for dev %d\n", idx);
+		return;
+	}
+
+	dev_dir = debugfs_create_dir(devname, nfcsim_debugfs_root);
+
+	debugfs_create_u8("dropframe", 0664, dev_dir, &dev->dropframe);
+}
+
+static struct nfcsim *nfcsim_device_new(struct nfcsim_link *link_in,
+					struct nfcsim_link *link_out)
+{
+	struct nfcsim *dev;
+	int rc;
+
+	dev = kzalloc_obj(struct nfcsim);
+	if (!dev)
+		return ERR_PTR(-ENOMEM);
+
+	INIT_DELAYED_WORK(&dev->send_work, nfcsim_send_wq);
+	INIT_WORK(&dev->recv_work, nfcsim_recv_wq);
+
+	dev->nfc_digital_dev =
+			nfc_digital_allocate_device(&nfcsim_digital_ops,
+						    NFC_PROTO_NFC_DEP_MASK,
+						    NFCSIM_CAPABILITIES,
+						    0, 0);
+	if (!dev->nfc_digital_dev) {
+		kfree(dev);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	nfc_digital_set_drvdata(dev->nfc_digital_dev, dev);
+
+	dev->link_in = link_in;
+	dev->link_out = link_out;
+
+	rc = nfc_digital_register_device(dev->nfc_digital_dev);
+	if (rc) {
+		pr_err("Could not register digital device (%d)\n", rc);
+		nfc_digital_free_device(dev->nfc_digital_dev);
+		kfree(dev);
+
+		return ERR_PTR(rc);
+	}
+
+	nfcsim_debugfs_init_dev(dev);
+
+	return dev;
+}
+
+static void nfcsim_device_free(struct nfcsim *dev)
+{
+	nfc_digital_unregister_device(dev->nfc_digital_dev);
+
+	dev->up = false;
+
+	nfcsim_link_shutdown(dev->link_in);
+
+	cancel_delayed_work_sync(&dev->send_work);
+	cancel_work_sync(&dev->recv_work);
+
+	nfc_digital_free_device(dev->nfc_digital_dev);
+
+	kfree(dev);
+}
+
+static struct nfcsim *dev0;
+static struct nfcsim *dev1;
+
+static int __init nfcsim_init(void)
+{
+	struct nfcsim_link *link0, *link1;
+	int rc;
+
+	link0 = nfcsim_link_new();
+	link1 = nfcsim_link_new();
+	if (!link0 || !link1) {
+		rc = -ENOMEM;
+		goto exit_err;
+	}
+
+	nfcsim_debugfs_init();
+
+	dev0 = nfcsim_device_new(link0, link1);
+	if (IS_ERR(dev0)) {
+		rc = PTR_ERR(dev0);
+		goto exit_err;
+	}
+
+	dev1 = nfcsim_device_new(link1, link0);
+	if (IS_ERR(dev1)) {
+		nfcsim_device_free(dev0);
+
+		rc = PTR_ERR(dev1);
+		goto exit_err;
+	}
+
+	pr_info("nfcsim " NFCSIM_VERSION " initialized\n");
+
+	return 0;
+
+exit_err:
+	pr_err("Failed to initialize nfcsim driver (%d)\n", rc);
+
+	if (link0)
+		nfcsim_link_free(link0);
+	if (link1)
+		nfcsim_link_free(link1);
+
+	return rc;
+}
+
+static void __exit nfcsim_exit(void)
+{
+	struct nfcsim_link *link0, *link1;
+
+	link0 = dev0->link_in;
+	link1 = dev0->link_out;
+
+	nfcsim_device_free(dev0);
+	nfcsim_device_free(dev1);
+
+	nfcsim_link_free(link0);
+	nfcsim_link_free(link1);
+
+	nfcsim_debugfs_remove();
+}
+
+module_init(nfcsim_init);
+module_exit(nfcsim_exit);
+
+MODULE_DESCRIPTION("NFCSim driver ver " NFCSIM_VERSION);
+MODULE_VERSION(NFCSIM_VERSION);
+MODULE_LICENSE("GPL");