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, 363 insertions, 0 deletions

diff --git a/net/atm/resources.c b/net/atm/resources.c
new file mode 100644
index 000000000..d94dc8221
--- /dev/null
+++ b/net/atm/resources.c
@@ -0,0 +1,363 @@
+// SPDX-License-Identifier: GPL-2.0
+/* net/atm/resources.c - Statically allocated resources */
+
+/* Written 1995-2000 by Werner Almesberger, EPFL LRC/ICA */
+
+/* Fixes
+ * Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ * 2002/01 - don't free the whole struct sock on sk->destruct time,
+ * 	     use the default destruct function initialized by sock_init_data */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ":%s: " fmt, __func__
+
+#include <linux/ctype.h>
+#include <linux/string.h>
+#include <linux/atmdev.h>
+#include <linux/kernel.h> /* for barrier */
+#include <linux/module.h>
+#include <linux/bitops.h>
+#include <linux/capability.h>
+#include <linux/delay.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+
+#include <net/sock.h>	 /* for struct sock */
+
+#include "common.h"
+#include "resources.h"
+
+
+LIST_HEAD(atm_devs);
+DEFINE_MUTEX(atm_dev_mutex);
+
+static struct atm_dev *__alloc_atm_dev(const char *type)
+{
+	struct atm_dev *dev;
+
+	dev = kzalloc_obj(*dev);
+	if (!dev)
+		return NULL;
+	dev->type = type;
+	dev->signal = ATM_PHY_SIG_UNKNOWN;
+	dev->link_rate = ATM_OC3_PCR;
+
+	return dev;
+}
+
+static struct atm_dev *__atm_dev_lookup(int number)
+{
+	struct atm_dev *dev;
+
+	list_for_each_entry(dev, &atm_devs, dev_list) {
+		if (dev->number == number) {
+			atm_dev_hold(dev);
+			return dev;
+		}
+	}
+	return NULL;
+}
+
+struct atm_dev *atm_dev_lookup(int number)
+{
+	struct atm_dev *dev;
+
+	mutex_lock(&atm_dev_mutex);
+	dev = __atm_dev_lookup(number);
+	mutex_unlock(&atm_dev_mutex);
+	return dev;
+}
+EXPORT_SYMBOL(atm_dev_lookup);
+
+struct atm_dev *atm_dev_register(const char *type, struct device *parent,
+				 const struct atmdev_ops *ops, int number,
+				 unsigned long *flags)
+{
+	struct atm_dev *dev, *inuse;
+
+	dev = __alloc_atm_dev(type);
+	if (!dev) {
+		pr_err("no space for dev %s\n", type);
+		return NULL;
+	}
+	mutex_lock(&atm_dev_mutex);
+	if (number != -1) {
+		inuse = __atm_dev_lookup(number);
+		if (inuse) {
+			atm_dev_put(inuse);
+			mutex_unlock(&atm_dev_mutex);
+			kfree(dev);
+			return NULL;
+		}
+		dev->number = number;
+	} else {
+		dev->number = 0;
+		while ((inuse = __atm_dev_lookup(dev->number))) {
+			atm_dev_put(inuse);
+			dev->number++;
+		}
+	}
+
+	dev->ops = ops;
+	if (flags)
+		dev->flags = *flags;
+	else
+		memset(&dev->flags, 0, sizeof(dev->flags));
+	memset(&dev->stats, 0, sizeof(dev->stats));
+	refcount_set(&dev->refcnt, 1);
+
+	if (atm_proc_dev_register(dev) < 0) {
+		pr_err("atm_proc_dev_register failed for dev %s\n", type);
+		mutex_unlock(&atm_dev_mutex);
+		kfree(dev);
+		return NULL;
+	}
+
+	if (atm_register_sysfs(dev, parent) < 0) {
+		pr_err("atm_register_sysfs failed for dev %s\n", type);
+		atm_proc_dev_deregister(dev);
+		goto out_fail;
+	}
+
+	list_add_tail(&dev->dev_list, &atm_devs);
+
+out:
+	mutex_unlock(&atm_dev_mutex);
+	return dev;
+
+out_fail:
+	put_device(&dev->class_dev);
+	dev = NULL;
+	goto out;
+}
+EXPORT_SYMBOL(atm_dev_register);
+
+void atm_dev_deregister(struct atm_dev *dev)
+{
+	BUG_ON(test_bit(ATM_DF_REMOVED, &dev->flags));
+	set_bit(ATM_DF_REMOVED, &dev->flags);
+
+	/*
+	 * if we remove current device from atm_devs list, new device
+	 * with same number can appear, such we need deregister proc,
+	 * release async all vccs and remove them from vccs list too
+	 */
+	mutex_lock(&atm_dev_mutex);
+	list_del(&dev->dev_list);
+	atm_dev_release_vccs(dev);
+	atm_unregister_sysfs(dev);
+	atm_proc_dev_deregister(dev);
+	mutex_unlock(&atm_dev_mutex);
+
+	atm_dev_put(dev);
+}
+EXPORT_SYMBOL(atm_dev_deregister);
+
+static void copy_aal_stats(struct k_atm_aal_stats *from,
+    struct atm_aal_stats *to)
+{
+#define __HANDLE_ITEM(i) to->i = atomic_read(&from->i)
+	__AAL_STAT_ITEMS
+#undef __HANDLE_ITEM
+}
+
+static void subtract_aal_stats(struct k_atm_aal_stats *from,
+    struct atm_aal_stats *to)
+{
+#define __HANDLE_ITEM(i) atomic_sub(to->i, &from->i)
+	__AAL_STAT_ITEMS
+#undef __HANDLE_ITEM
+}
+
+static int fetch_stats(struct atm_dev *dev, struct atm_dev_stats __user *arg,
+		       int zero)
+{
+	struct atm_dev_stats tmp;
+	int error = 0;
+
+	copy_aal_stats(&dev->stats.aal0, &tmp.aal0);
+	copy_aal_stats(&dev->stats.aal34, &tmp.aal34);
+	copy_aal_stats(&dev->stats.aal5, &tmp.aal5);
+	if (arg)
+		error = copy_to_user(arg, &tmp, sizeof(tmp));
+	if (zero && !error) {
+		subtract_aal_stats(&dev->stats.aal0, &tmp.aal0);
+		subtract_aal_stats(&dev->stats.aal34, &tmp.aal34);
+		subtract_aal_stats(&dev->stats.aal5, &tmp.aal5);
+	}
+	return error ? -EFAULT : 0;
+}
+
+int atm_getnames(void __user *buf, int __user *iobuf_len)
+{
+	int error, len, size = 0;
+	struct atm_dev *dev;
+	struct list_head *p;
+	int *tmp_buf, *tmp_p;
+
+	if (get_user(len, iobuf_len))
+		return -EFAULT;
+	mutex_lock(&atm_dev_mutex);
+	list_for_each(p, &atm_devs)
+		size += sizeof(int);
+	if (size > len) {
+		mutex_unlock(&atm_dev_mutex);
+		return -E2BIG;
+	}
+	tmp_buf = kmalloc(size, GFP_ATOMIC);
+	if (!tmp_buf) {
+		mutex_unlock(&atm_dev_mutex);
+		return -ENOMEM;
+	}
+	tmp_p = tmp_buf;
+	list_for_each_entry(dev, &atm_devs, dev_list) {
+		*tmp_p++ = dev->number;
+	}
+	mutex_unlock(&atm_dev_mutex);
+	error = ((copy_to_user(buf, tmp_buf, size)) ||
+		 put_user(size, iobuf_len))
+		? -EFAULT : 0;
+	kfree(tmp_buf);
+	return error;
+}
+
+int atm_dev_ioctl(unsigned int cmd, void __user *buf, int __user *sioc_len,
+		  int number, int compat)
+{
+	struct atm_dev *dev;
+	int error, size = 0;
+
+	dev = try_then_request_module(atm_dev_lookup(number), "atm-device-%d",
+				      number);
+	if (!dev)
+		return -ENODEV;
+
+	switch (cmd) {
+	case ATM_GETTYPE:
+		size = strlen(dev->type) + 1;
+		if (copy_to_user(buf, dev->type, size)) {
+			error = -EFAULT;
+			goto done;
+		}
+		break;
+	case ATM_GETESI:
+		size = ESI_LEN;
+		if (copy_to_user(buf, dev->esi, size)) {
+			error = -EFAULT;
+			goto done;
+		}
+		break;
+	case ATM_SETESI:
+	{
+		int i;
+
+		for (i = 0; i < ESI_LEN; i++)
+			if (dev->esi[i]) {
+				error = -EEXIST;
+				goto done;
+			}
+	}
+		fallthrough;
+	case ATM_SETESIF:
+	{
+		unsigned char esi[ESI_LEN];
+
+		if (!capable(CAP_NET_ADMIN)) {
+			error = -EPERM;
+			goto done;
+		}
+		if (copy_from_user(esi, buf, ESI_LEN)) {
+			error = -EFAULT;
+			goto done;
+		}
+		memcpy(dev->esi, esi, ESI_LEN);
+		error =  ESI_LEN;
+		goto done;
+	}
+	case ATM_GETSTATZ:
+		if (!capable(CAP_NET_ADMIN)) {
+			error = -EPERM;
+			goto done;
+		}
+		fallthrough;
+	case ATM_GETSTAT:
+		size = sizeof(struct atm_dev_stats);
+		error = fetch_stats(dev, buf, cmd == ATM_GETSTATZ);
+		if (error)
+			goto done;
+		break;
+	case ATM_GETCIRANGE:
+		size = sizeof(struct atm_cirange);
+		if (copy_to_user(buf, &dev->ci_range, size)) {
+			error = -EFAULT;
+			goto done;
+		}
+		break;
+	case ATM_GETLINKRATE:
+		size = sizeof(int);
+		if (copy_to_user(buf, &dev->link_rate, size)) {
+			error = -EFAULT;
+			goto done;
+		}
+		break;
+	case ATM_SETLOOP:
+		if (__ATM_LM_XTRMT((int) (unsigned long) buf) &&
+		    __ATM_LM_XTLOC((int) (unsigned long) buf) >
+		    __ATM_LM_XTRMT((int) (unsigned long) buf)) {
+			error = -EINVAL;
+			goto done;
+		}
+		fallthrough;
+	case ATM_SETCIRANGE:
+		if (!capable(CAP_NET_ADMIN)) {
+			error = -EPERM;
+			goto done;
+		}
+		fallthrough;
+	default:
+		if (IS_ENABLED(CONFIG_COMPAT) && compat) {
+#ifdef CONFIG_COMPAT
+			if (!dev->ops->compat_ioctl) {
+				error = -EINVAL;
+				goto done;
+			}
+			size = dev->ops->compat_ioctl(dev, cmd, buf);
+#endif
+		} else {
+			if (!dev->ops->ioctl) {
+				error = -EINVAL;
+				goto done;
+			}
+			size = dev->ops->ioctl(dev, cmd, buf);
+		}
+		if (size < 0) {
+			error = (size == -ENOIOCTLCMD ? -ENOTTY : size);
+			goto done;
+		}
+	}
+
+	if (size)
+		error = put_user(size, sioc_len) ? -EFAULT : 0;
+	else
+		error = 0;
+done:
+	atm_dev_put(dev);
+	return error;
+}
+
+#ifdef CONFIG_PROC_FS
+void *atm_dev_seq_start(struct seq_file *seq, loff_t *pos)
+{
+	mutex_lock(&atm_dev_mutex);
+	return seq_list_start_head(&atm_devs, *pos);
+}
+
+void atm_dev_seq_stop(struct seq_file *seq, void *v)
+{
+	mutex_unlock(&atm_dev_mutex);
+}
+
+void *atm_dev_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+	return seq_list_next(v, &atm_devs, pos);
+}
+#endif