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, 536 insertions, 0 deletions

diff --git a/drivers/char/nvram.c b/drivers/char/nvram.c
new file mode 100644
index 000000000..e89cc1f1c
--- /dev/null
+++ b/drivers/char/nvram.c
@@ -0,0 +1,536 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * CMOS/NV-RAM driver for Linux
+ *
+ * Copyright (C) 1997 Roman Hodek <Roman.Hodek@informatik.uni-erlangen.de>
+ * idea by and with help from Richard Jelinek <rj@suse.de>
+ * Portions copyright (c) 2001,2002 Sun Microsystems (thockin@sun.com)
+ *
+ * This driver allows you to access the contents of the non-volatile memory in
+ * the mc146818rtc.h real-time clock. This chip is built into all PCs and into
+ * many Atari machines. In the former it's called "CMOS-RAM", in the latter
+ * "NVRAM" (NV stands for non-volatile).
+ *
+ * The data are supplied as a (seekable) character device, /dev/nvram. The
+ * size of this file is dependent on the controller.  The usual size is 114,
+ * the number of freely available bytes in the memory (i.e., not used by the
+ * RTC itself).
+ *
+ * Checksums over the NVRAM contents are managed by this driver. In case of a
+ * bad checksum, reads and writes return -EIO. The checksum can be initialized
+ * to a sane state either by ioctl(NVRAM_INIT) (clear whole NVRAM) or
+ * ioctl(NVRAM_SETCKS) (doesn't change contents, just makes checksum valid
+ * again; use with care!)
+ *
+ * 	1.1	Cesar Barros: SMP locking fixes
+ * 		added changelog
+ * 	1.2	Erik Gilling: Cobalt Networks support
+ * 		Tim Hockin: general cleanup, Cobalt support
+ * 	1.3	Wim Van Sebroeck: convert PRINT_PROC to seq_file
+ */
+
+#define NVRAM_VERSION	"1.3"
+
+#include <linux/module.h>
+#include <linux/nvram.h>
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/miscdevice.h>
+#include <linux/ioport.h>
+#include <linux/fcntl.h>
+#include <linux/mc146818rtc.h>
+#include <linux/init.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/io.h>
+#include <linux/uaccess.h>
+#include <linux/mutex.h>
+#include <linux/pagemap.h>
+
+#ifdef CONFIG_PPC
+#include <asm/nvram.h>
+#endif
+
+static DEFINE_SPINLOCK(nvram_state_lock);
+static int nvram_open_cnt;	/* #times opened */
+static int nvram_open_mode;	/* special open modes */
+static ssize_t nvram_size;
+#define NVRAM_WRITE		1 /* opened for writing (exclusive) */
+#define NVRAM_EXCL		2 /* opened with O_EXCL */
+
+#ifdef CONFIG_X86
+/*
+ * These functions are provided to be called internally or by other parts of
+ * the kernel. It's up to the caller to ensure correct checksum before reading
+ * or after writing (needs to be done only once).
+ *
+ * It is worth noting that these functions all access bytes of general
+ * purpose memory in the NVRAM - that is to say, they all add the
+ * NVRAM_FIRST_BYTE offset.  Pass them offsets into NVRAM as if you did not
+ * know about the RTC cruft.
+ */
+
+#define NVRAM_BYTES		(128 - NVRAM_FIRST_BYTE)
+
+/* Note that *all* calls to CMOS_READ and CMOS_WRITE must be done with
+ * rtc_lock held. Due to the index-port/data-port design of the RTC, we
+ * don't want two different things trying to get to it at once. (e.g. the
+ * periodic 11 min sync from kernel/time/ntp.c vs. this driver.)
+ */
+
+static unsigned char __nvram_read_byte(int i)
+{
+	return CMOS_READ(NVRAM_FIRST_BYTE + i);
+}
+
+static unsigned char pc_nvram_read_byte(int i)
+{
+	unsigned long flags;
+	unsigned char c;
+
+	spin_lock_irqsave(&rtc_lock, flags);
+	c = __nvram_read_byte(i);
+	spin_unlock_irqrestore(&rtc_lock, flags);
+	return c;
+}
+
+/* This races nicely with trying to read with checksum checking (nvram_read) */
+static void __nvram_write_byte(unsigned char c, int i)
+{
+	CMOS_WRITE(c, NVRAM_FIRST_BYTE + i);
+}
+
+static void pc_nvram_write_byte(unsigned char c, int i)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&rtc_lock, flags);
+	__nvram_write_byte(c, i);
+	spin_unlock_irqrestore(&rtc_lock, flags);
+}
+
+/* On PCs, the checksum is built only over bytes 2..31 */
+#define PC_CKS_RANGE_START	2
+#define PC_CKS_RANGE_END	31
+#define PC_CKS_LOC		32
+
+static int __nvram_check_checksum(void)
+{
+	int i;
+	unsigned short sum = 0;
+	unsigned short expect;
+
+	for (i = PC_CKS_RANGE_START; i <= PC_CKS_RANGE_END; ++i)
+		sum += __nvram_read_byte(i);
+	expect = __nvram_read_byte(PC_CKS_LOC)<<8 |
+	    __nvram_read_byte(PC_CKS_LOC+1);
+	return (sum & 0xffff) == expect;
+}
+
+static void __nvram_set_checksum(void)
+{
+	int i;
+	unsigned short sum = 0;
+
+	for (i = PC_CKS_RANGE_START; i <= PC_CKS_RANGE_END; ++i)
+		sum += __nvram_read_byte(i);
+	__nvram_write_byte(sum >> 8, PC_CKS_LOC);
+	__nvram_write_byte(sum & 0xff, PC_CKS_LOC + 1);
+}
+
+static long pc_nvram_set_checksum(void)
+{
+	spin_lock_irq(&rtc_lock);
+	__nvram_set_checksum();
+	spin_unlock_irq(&rtc_lock);
+	return 0;
+}
+
+static long pc_nvram_initialize(void)
+{
+	ssize_t i;
+
+	spin_lock_irq(&rtc_lock);
+	for (i = 0; i < NVRAM_BYTES; ++i)
+		__nvram_write_byte(0, i);
+	__nvram_set_checksum();
+	spin_unlock_irq(&rtc_lock);
+	return 0;
+}
+
+static ssize_t pc_nvram_get_size(void)
+{
+	return NVRAM_BYTES;
+}
+
+static ssize_t pc_nvram_read(char *buf, size_t count, loff_t *ppos)
+{
+	char *p = buf;
+	loff_t i;
+
+	spin_lock_irq(&rtc_lock);
+	if (!__nvram_check_checksum()) {
+		spin_unlock_irq(&rtc_lock);
+		return -EIO;
+	}
+	for (i = *ppos; count > 0 && i < NVRAM_BYTES; --count, ++i, ++p)
+		*p = __nvram_read_byte(i);
+	spin_unlock_irq(&rtc_lock);
+
+	*ppos = i;
+	return p - buf;
+}
+
+static ssize_t pc_nvram_write(char *buf, size_t count, loff_t *ppos)
+{
+	char *p = buf;
+	loff_t i;
+
+	spin_lock_irq(&rtc_lock);
+	if (!__nvram_check_checksum()) {
+		spin_unlock_irq(&rtc_lock);
+		return -EIO;
+	}
+	for (i = *ppos; count > 0 && i < NVRAM_BYTES; --count, ++i, ++p)
+		__nvram_write_byte(*p, i);
+	__nvram_set_checksum();
+	spin_unlock_irq(&rtc_lock);
+
+	*ppos = i;
+	return p - buf;
+}
+
+const struct nvram_ops arch_nvram_ops = {
+	.read           = pc_nvram_read,
+	.write          = pc_nvram_write,
+	.read_byte      = pc_nvram_read_byte,
+	.write_byte     = pc_nvram_write_byte,
+	.get_size       = pc_nvram_get_size,
+	.set_checksum   = pc_nvram_set_checksum,
+	.initialize     = pc_nvram_initialize,
+};
+EXPORT_SYMBOL(arch_nvram_ops);
+#endif /* CONFIG_X86 */
+
+/*
+ * The are the file operation function for user access to /dev/nvram
+ */
+
+static loff_t nvram_misc_llseek(struct file *file, loff_t offset, int origin)
+{
+	return generic_file_llseek_size(file, offset, origin, MAX_LFS_FILESIZE,
+					nvram_size);
+}
+
+static ssize_t nvram_misc_read(struct file *file, char __user *buf,
+			       size_t count, loff_t *ppos)
+{
+	char *tmp;
+	ssize_t ret;
+
+
+	if (*ppos >= nvram_size)
+		return 0;
+
+	count = min_t(size_t, count, nvram_size - *ppos);
+	count = min_t(size_t, count, PAGE_SIZE);
+
+	tmp = kmalloc(count, GFP_KERNEL);
+	if (!tmp)
+		return -ENOMEM;
+
+	ret = nvram_read(tmp, count, ppos);
+	if (ret <= 0)
+		goto out;
+
+	if (copy_to_user(buf, tmp, ret)) {
+		*ppos -= ret;
+		ret = -EFAULT;
+	}
+
+out:
+	kfree(tmp);
+	return ret;
+}
+
+static ssize_t nvram_misc_write(struct file *file, const char __user *buf,
+				size_t count, loff_t *ppos)
+{
+	char *tmp;
+	ssize_t ret;
+
+	if (*ppos >= nvram_size)
+		return 0;
+
+	count = min_t(size_t, count, nvram_size - *ppos);
+	count = min_t(size_t, count, PAGE_SIZE);
+
+	tmp = memdup_user(buf, count);
+	if (IS_ERR(tmp))
+		return PTR_ERR(tmp);
+
+	ret = nvram_write(tmp, count, ppos);
+	kfree(tmp);
+	return ret;
+}
+
+static long nvram_misc_ioctl(struct file *file, unsigned int cmd,
+			     unsigned long arg)
+{
+	long ret = -ENOTTY;
+
+	switch (cmd) {
+#ifdef CONFIG_PPC
+	case OBSOLETE_PMAC_NVRAM_GET_OFFSET:
+		pr_warn("nvram: Using obsolete PMAC_NVRAM_GET_OFFSET ioctl\n");
+		fallthrough;
+	case IOC_NVRAM_GET_OFFSET:
+		ret = -EINVAL;
+#ifdef CONFIG_PPC_PMAC
+		if (machine_is(powermac)) {
+			int part, offset;
+
+			if (copy_from_user(&part, (void __user *)arg,
+					   sizeof(part)) != 0)
+				return -EFAULT;
+			if (part < pmac_nvram_OF || part > pmac_nvram_NR)
+				return -EINVAL;
+			offset = pmac_get_partition(part);
+			if (offset < 0)
+				return -EINVAL;
+			if (copy_to_user((void __user *)arg,
+					 &offset, sizeof(offset)) != 0)
+				return -EFAULT;
+			ret = 0;
+		}
+#endif
+		break;
+#ifdef CONFIG_PPC32
+	case IOC_NVRAM_SYNC:
+		if (ppc_md.nvram_sync)
+			ppc_md.nvram_sync();
+		ret = 0;
+		break;
+#endif
+#elif defined(CONFIG_X86) || defined(CONFIG_M68K)
+	case NVRAM_INIT:
+		/* initialize NVRAM contents and checksum */
+		if (!capable(CAP_SYS_ADMIN))
+			return -EACCES;
+
+		if (arch_nvram_ops.initialize)
+			ret = arch_nvram_ops.initialize();
+		break;
+	case NVRAM_SETCKS:
+		/* just set checksum, contents unchanged (maybe useful after
+		 * checksum garbaged somehow...) */
+		if (!capable(CAP_SYS_ADMIN))
+			return -EACCES;
+
+		if (arch_nvram_ops.set_checksum)
+			ret = arch_nvram_ops.set_checksum();
+		break;
+#endif /* CONFIG_X86 || CONFIG_M68K */
+	}
+	return ret;
+}
+
+static int nvram_misc_open(struct inode *inode, struct file *file)
+{
+	spin_lock(&nvram_state_lock);
+
+	/* Prevent multiple readers/writers if desired. */
+	if ((nvram_open_cnt && (file->f_flags & O_EXCL)) ||
+	    (nvram_open_mode & NVRAM_EXCL)) {
+		spin_unlock(&nvram_state_lock);
+		return -EBUSY;
+	}
+
+#if defined(CONFIG_X86) || defined(CONFIG_M68K)
+	/* Prevent multiple writers if the set_checksum ioctl is implemented. */
+	if ((arch_nvram_ops.set_checksum != NULL) &&
+	    (file->f_mode & FMODE_WRITE) && (nvram_open_mode & NVRAM_WRITE)) {
+		spin_unlock(&nvram_state_lock);
+		return -EBUSY;
+	}
+#endif
+
+	if (file->f_flags & O_EXCL)
+		nvram_open_mode |= NVRAM_EXCL;
+	if (file->f_mode & FMODE_WRITE)
+		nvram_open_mode |= NVRAM_WRITE;
+	nvram_open_cnt++;
+
+	spin_unlock(&nvram_state_lock);
+
+	return 0;
+}
+
+static int nvram_misc_release(struct inode *inode, struct file *file)
+{
+	spin_lock(&nvram_state_lock);
+
+	nvram_open_cnt--;
+
+	/* if only one instance is open, clear the EXCL bit */
+	if (nvram_open_mode & NVRAM_EXCL)
+		nvram_open_mode &= ~NVRAM_EXCL;
+	if (file->f_mode & FMODE_WRITE)
+		nvram_open_mode &= ~NVRAM_WRITE;
+
+	spin_unlock(&nvram_state_lock);
+
+	return 0;
+}
+
+#if defined(CONFIG_X86) && defined(CONFIG_PROC_FS)
+static const char * const floppy_types[] = {
+	"none", "5.25'' 360k", "5.25'' 1.2M", "3.5'' 720k", "3.5'' 1.44M",
+	"3.5'' 2.88M", "3.5'' 2.88M"
+};
+
+static const char * const gfx_types[] = {
+	"EGA, VGA, ... (with BIOS)",
+	"CGA (40 cols)",
+	"CGA (80 cols)",
+	"monochrome",
+};
+
+static void pc_nvram_proc_read(unsigned char *nvram, struct seq_file *seq,
+			       void *offset)
+{
+	int checksum;
+	int type;
+
+	spin_lock_irq(&rtc_lock);
+	checksum = __nvram_check_checksum();
+	spin_unlock_irq(&rtc_lock);
+
+	seq_printf(seq, "Checksum status: %svalid\n", checksum ? "" : "not ");
+
+	seq_printf(seq, "# floppies     : %d\n",
+	    (nvram[6] & 1) ? (nvram[6] >> 6) + 1 : 0);
+	seq_printf(seq, "Floppy 0 type  : ");
+	type = nvram[2] >> 4;
+	if (type < ARRAY_SIZE(floppy_types))
+		seq_printf(seq, "%s\n", floppy_types[type]);
+	else
+		seq_printf(seq, "%d (unknown)\n", type);
+	seq_printf(seq, "Floppy 1 type  : ");
+	type = nvram[2] & 0x0f;
+	if (type < ARRAY_SIZE(floppy_types))
+		seq_printf(seq, "%s\n", floppy_types[type]);
+	else
+		seq_printf(seq, "%d (unknown)\n", type);
+
+	seq_printf(seq, "HD 0 type      : ");
+	type = nvram[4] >> 4;
+	if (type)
+		seq_printf(seq, "%02x\n", type == 0x0f ? nvram[11] : type);
+	else
+		seq_printf(seq, "none\n");
+
+	seq_printf(seq, "HD 1 type      : ");
+	type = nvram[4] & 0x0f;
+	if (type)
+		seq_printf(seq, "%02x\n", type == 0x0f ? nvram[12] : type);
+	else
+		seq_printf(seq, "none\n");
+
+	seq_printf(seq, "HD type 48 data: %d/%d/%d C/H/S, precomp %d, lz %d\n",
+	    nvram[18] | (nvram[19] << 8),
+	    nvram[20], nvram[25],
+	    nvram[21] | (nvram[22] << 8), nvram[23] | (nvram[24] << 8));
+	seq_printf(seq, "HD type 49 data: %d/%d/%d C/H/S, precomp %d, lz %d\n",
+	    nvram[39] | (nvram[40] << 8),
+	    nvram[41], nvram[46],
+	    nvram[42] | (nvram[43] << 8), nvram[44] | (nvram[45] << 8));
+
+	seq_printf(seq, "DOS base memory: %d kB\n", nvram[7] | (nvram[8] << 8));
+	seq_printf(seq, "Extended memory: %d kB (configured), %d kB (tested)\n",
+	    nvram[9] | (nvram[10] << 8), nvram[34] | (nvram[35] << 8));
+
+	seq_printf(seq, "Gfx adapter    : %s\n",
+	    gfx_types[(nvram[6] >> 4) & 3]);
+
+	seq_printf(seq, "FPU            : %sinstalled\n",
+	    (nvram[6] & 2) ? "" : "not ");
+
+	return;
+}
+
+static int nvram_proc_read(struct seq_file *seq, void *offset)
+{
+	unsigned char contents[NVRAM_BYTES];
+	int i = 0;
+
+	spin_lock_irq(&rtc_lock);
+	for (i = 0; i < NVRAM_BYTES; ++i)
+		contents[i] = __nvram_read_byte(i);
+	spin_unlock_irq(&rtc_lock);
+
+	pc_nvram_proc_read(contents, seq, offset);
+
+	return 0;
+}
+#endif /* CONFIG_X86 && CONFIG_PROC_FS */
+
+static const struct file_operations nvram_misc_fops = {
+	.owner		= THIS_MODULE,
+	.llseek		= nvram_misc_llseek,
+	.read		= nvram_misc_read,
+	.write		= nvram_misc_write,
+	.unlocked_ioctl	= nvram_misc_ioctl,
+	.open		= nvram_misc_open,
+	.release	= nvram_misc_release,
+};
+
+static struct miscdevice nvram_misc = {
+	NVRAM_MINOR,
+	"nvram",
+	&nvram_misc_fops,
+};
+
+static int __init nvram_module_init(void)
+{
+	int ret;
+
+	nvram_size = nvram_get_size();
+	if (nvram_size < 0)
+		return nvram_size;
+
+	ret = misc_register(&nvram_misc);
+	if (ret) {
+		pr_err("nvram: can't misc_register on minor=%d\n", NVRAM_MINOR);
+		return ret;
+	}
+
+#if defined(CONFIG_X86) && defined(CONFIG_PROC_FS)
+	if (!proc_create_single("driver/nvram", 0, NULL, nvram_proc_read)) {
+		pr_err("nvram: can't create /proc/driver/nvram\n");
+		misc_deregister(&nvram_misc);
+		return -ENOMEM;
+	}
+#endif
+
+	pr_info("Non-volatile memory driver v" NVRAM_VERSION "\n");
+	return 0;
+}
+
+static void __exit nvram_module_exit(void)
+{
+#if defined(CONFIG_X86) && defined(CONFIG_PROC_FS)
+	remove_proc_entry("driver/nvram", NULL);
+#endif
+	misc_deregister(&nvram_misc);
+}
+
+module_init(nvram_module_init);
+module_exit(nvram_module_exit);
+
+MODULE_DESCRIPTION("CMOS/NV-RAM driver for Linux");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS_MISCDEV(NVRAM_MINOR);
+MODULE_ALIAS("devname:nvram");