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, 424 insertions, 0 deletions

diff --git a/drivers/char/ds1620.c b/drivers/char/ds1620.c
new file mode 100644
index 000000000..44a1cdbd4
--- /dev/null
+++ b/drivers/char/ds1620.c
@@ -0,0 +1,424 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * linux/drivers/char/ds1620.c: Dallas Semiconductors DS1620
+ *   thermometer driver (as used in the Rebel.com NetWinder)
+ */
+#include <linux/module.h>
+#include <linux/miscdevice.h>
+#include <linux/delay.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/capability.h>
+#include <linux/init.h>
+#include <linux/mutex.h>
+
+#include <mach/hardware.h>
+#include <asm/mach-types.h>
+#include <linux/uaccess.h>
+#include <asm/therm.h>
+
+#ifdef CONFIG_PROC_FS
+/* define for /proc interface */
+#define THERM_USE_PROC
+#endif
+
+/* Definitions for DS1620 chip */
+#define THERM_START_CONVERT	0xee
+#define THERM_RESET		0xaf
+#define THERM_READ_CONFIG	0xac
+#define THERM_READ_TEMP		0xaa
+#define THERM_READ_TL		0xa2
+#define THERM_READ_TH		0xa1
+#define THERM_WRITE_CONFIG	0x0c
+#define THERM_WRITE_TL		0x02
+#define THERM_WRITE_TH		0x01
+
+#define CFG_CPU			2
+#define CFG_1SHOT		1
+
+static DEFINE_MUTEX(ds1620_mutex);
+static const char *fan_state[] = { "off", "on", "on (hardwired)" };
+
+/*
+ * Start of NetWinder specifics
+ *  Note!  We have to hold the gpio lock with IRQs disabled over the
+ *  whole of our transaction to the Dallas chip, since there is a
+ *  chance that the WaveArtist driver could touch these bits to
+ *  enable or disable the speaker.
+ */
+extern unsigned int system_rev;
+
+static inline void netwinder_ds1620_set_clk(int clk)
+{
+	nw_gpio_modify_op(GPIO_DSCLK, clk ? GPIO_DSCLK : 0);
+}
+
+static inline void netwinder_ds1620_set_data(int dat)
+{
+	nw_gpio_modify_op(GPIO_DATA, dat ? GPIO_DATA : 0);
+}
+
+static inline int netwinder_ds1620_get_data(void)
+{
+	return nw_gpio_read() & GPIO_DATA;
+}
+
+static inline void netwinder_ds1620_set_data_dir(int dir)
+{
+	nw_gpio_modify_io(GPIO_DATA, dir ? GPIO_DATA : 0);
+}
+
+static inline void netwinder_ds1620_reset(void)
+{
+	nw_cpld_modify(CPLD_DS_ENABLE, 0);
+	nw_cpld_modify(CPLD_DS_ENABLE, CPLD_DS_ENABLE);
+}
+
+static inline void netwinder_lock(unsigned long *flags)
+{
+	raw_spin_lock_irqsave(&nw_gpio_lock, *flags);
+}
+
+static inline void netwinder_unlock(unsigned long *flags)
+{
+	raw_spin_unlock_irqrestore(&nw_gpio_lock, *flags);
+}
+
+static inline void netwinder_set_fan(int i)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&nw_gpio_lock, flags);
+	nw_gpio_modify_op(GPIO_FAN, i ? GPIO_FAN : 0);
+	raw_spin_unlock_irqrestore(&nw_gpio_lock, flags);
+}
+
+static inline int netwinder_get_fan(void)
+{
+	if ((system_rev & 0xf000) == 0x4000)
+		return FAN_ALWAYS_ON;
+
+	return (nw_gpio_read() & GPIO_FAN) ? FAN_ON : FAN_OFF;
+}
+
+/*
+ * End of NetWinder specifics
+ */
+
+static void ds1620_send_bits(int nr, int value)
+{
+	int i;
+
+	for (i = 0; i < nr; i++) {
+		netwinder_ds1620_set_data(value & 1);
+		netwinder_ds1620_set_clk(0);
+		udelay(1);
+		netwinder_ds1620_set_clk(1);
+		udelay(1);
+
+		value >>= 1;
+	}
+}
+
+static unsigned int ds1620_recv_bits(int nr)
+{
+	unsigned int value = 0, mask = 1;
+	int i;
+
+	netwinder_ds1620_set_data(0);
+
+	for (i = 0; i < nr; i++) {
+		netwinder_ds1620_set_clk(0);
+		udelay(1);
+
+		if (netwinder_ds1620_get_data())
+			value |= mask;
+
+		mask <<= 1;
+
+		netwinder_ds1620_set_clk(1);
+		udelay(1);
+	}
+
+	return value;
+}
+
+static void ds1620_out(int cmd, int bits, int value)
+{
+	unsigned long flags;
+
+	netwinder_lock(&flags);
+	netwinder_ds1620_set_clk(1);
+	netwinder_ds1620_set_data_dir(0);
+	netwinder_ds1620_reset();
+
+	udelay(1);
+
+	ds1620_send_bits(8, cmd);
+	if (bits)
+		ds1620_send_bits(bits, value);
+
+	udelay(1);
+
+	netwinder_ds1620_reset();
+	netwinder_unlock(&flags);
+
+	msleep(20);
+}
+
+static unsigned int ds1620_in(int cmd, int bits)
+{
+	unsigned long flags;
+	unsigned int value;
+
+	netwinder_lock(&flags);
+	netwinder_ds1620_set_clk(1);
+	netwinder_ds1620_set_data_dir(0);
+	netwinder_ds1620_reset();
+
+	udelay(1);
+
+	ds1620_send_bits(8, cmd);
+
+	netwinder_ds1620_set_data_dir(1);
+	value = ds1620_recv_bits(bits);
+
+	netwinder_ds1620_reset();
+	netwinder_unlock(&flags);
+
+	return value;
+}
+
+static int cvt_9_to_int(unsigned int val)
+{
+	if (val & 0x100)
+		val |= 0xfffffe00;
+
+	return val;
+}
+
+static void ds1620_write_state(struct therm *therm)
+{
+	ds1620_out(THERM_WRITE_CONFIG, 8, CFG_CPU);
+	ds1620_out(THERM_WRITE_TL, 9, therm->lo);
+	ds1620_out(THERM_WRITE_TH, 9, therm->hi);
+	ds1620_out(THERM_START_CONVERT, 0, 0);
+}
+
+static void ds1620_read_state(struct therm *therm)
+{
+	therm->lo = cvt_9_to_int(ds1620_in(THERM_READ_TL, 9));
+	therm->hi = cvt_9_to_int(ds1620_in(THERM_READ_TH, 9));
+}
+
+static int ds1620_open(struct inode *inode, struct file *file)
+{
+	return stream_open(inode, file);
+}
+
+static ssize_t
+ds1620_read(struct file *file, char __user *buf, size_t count, loff_t *ptr)
+{
+	signed int cur_temp;
+	signed char cur_temp_degF;
+
+	cur_temp = cvt_9_to_int(ds1620_in(THERM_READ_TEMP, 9)) >> 1;
+
+	/* convert to Fahrenheit, as per wdt.c */
+	cur_temp_degF = (cur_temp * 9) / 5 + 32;
+
+	if (copy_to_user(buf, &cur_temp_degF, 1))
+		return -EFAULT;
+
+	return 1;
+}
+
+static int
+ds1620_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	struct therm therm;
+	union {
+		struct therm __user *therm;
+		int __user *i;
+	} uarg;
+	int i;
+
+	uarg.i = (int __user *)arg;
+
+	switch(cmd) {
+	case CMD_SET_THERMOSTATE:
+	case CMD_SET_THERMOSTATE2:
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+
+		if (cmd == CMD_SET_THERMOSTATE) {
+			if (get_user(therm.hi, uarg.i))
+				return -EFAULT;
+			therm.lo = therm.hi - 3;
+		} else {
+			if (copy_from_user(&therm, uarg.therm, sizeof(therm)))
+				return -EFAULT;
+		}
+
+		therm.lo <<= 1;
+		therm.hi <<= 1;
+
+		ds1620_write_state(&therm);
+		break;
+
+	case CMD_GET_THERMOSTATE:
+	case CMD_GET_THERMOSTATE2:
+		ds1620_read_state(&therm);
+
+		therm.lo >>= 1;
+		therm.hi >>= 1;
+
+		if (cmd == CMD_GET_THERMOSTATE) {
+			if (put_user(therm.hi, uarg.i))
+				return -EFAULT;
+		} else {
+			if (copy_to_user(uarg.therm, &therm, sizeof(therm)))
+				return -EFAULT;
+		}
+		break;
+
+	case CMD_GET_TEMPERATURE:
+	case CMD_GET_TEMPERATURE2:
+		i = cvt_9_to_int(ds1620_in(THERM_READ_TEMP, 9));
+
+		if (cmd == CMD_GET_TEMPERATURE)
+			i >>= 1;
+
+		return put_user(i, uarg.i) ? -EFAULT : 0;
+
+	case CMD_GET_STATUS:
+		i = ds1620_in(THERM_READ_CONFIG, 8) & 0xe3;
+
+		return put_user(i, uarg.i) ? -EFAULT : 0;
+
+	case CMD_GET_FAN:
+		i = netwinder_get_fan();
+
+		return put_user(i, uarg.i) ? -EFAULT : 0;
+
+	case CMD_SET_FAN:
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+
+		if (get_user(i, uarg.i))
+			return -EFAULT;
+
+		netwinder_set_fan(i);
+		break;
+		
+	default:
+		return -ENOIOCTLCMD;
+	}
+
+	return 0;
+}
+
+static long
+ds1620_unlocked_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	int ret;
+
+	mutex_lock(&ds1620_mutex);
+	ret = ds1620_ioctl(file, cmd, arg);
+	mutex_unlock(&ds1620_mutex);
+
+	return ret;
+}
+
+#ifdef THERM_USE_PROC
+static int ds1620_proc_therm_show(struct seq_file *m, void *v)
+{
+	struct therm th;
+	int temp;
+
+	ds1620_read_state(&th);
+	temp =  cvt_9_to_int(ds1620_in(THERM_READ_TEMP, 9));
+
+	seq_printf(m, "Thermostat: HI %i.%i, LOW %i.%i; temperature: %i.%i C, fan %s\n",
+		   th.hi >> 1, th.hi & 1 ? 5 : 0,
+		   th.lo >> 1, th.lo & 1 ? 5 : 0,
+		   temp  >> 1, temp  & 1 ? 5 : 0,
+		   fan_state[netwinder_get_fan()]);
+	return 0;
+}
+#endif
+
+static const struct file_operations ds1620_fops = {
+	.owner		= THIS_MODULE,
+	.open		= ds1620_open,
+	.read		= ds1620_read,
+	.unlocked_ioctl	= ds1620_unlocked_ioctl,
+};
+
+static struct miscdevice ds1620_miscdev = {
+	TEMP_MINOR,
+	"temp",
+	&ds1620_fops
+};
+
+static int __init ds1620_init(void)
+{
+	int ret;
+	struct therm th, th_start;
+
+	if (!machine_is_netwinder())
+		return -ENODEV;
+
+	ds1620_out(THERM_RESET, 0, 0);
+	ds1620_out(THERM_WRITE_CONFIG, 8, CFG_CPU);
+	ds1620_out(THERM_START_CONVERT, 0, 0);
+
+	/*
+	 * Trigger the fan to start by setting
+	 * temperature high point low.  This kicks
+	 * the fan into action.
+	 */
+	ds1620_read_state(&th);
+	th_start.lo = 0;
+	th_start.hi = 1;
+	ds1620_write_state(&th_start);
+
+	msleep(2000);
+
+	ds1620_write_state(&th);
+
+	ret = misc_register(&ds1620_miscdev);
+	if (ret < 0)
+		return ret;
+
+#ifdef THERM_USE_PROC
+	if (!proc_create_single("therm", 0, NULL, ds1620_proc_therm_show))
+		printk(KERN_ERR "therm: unable to register /proc/therm\n");
+#endif
+
+	ds1620_read_state(&th);
+	ret = cvt_9_to_int(ds1620_in(THERM_READ_TEMP, 9));
+
+	printk(KERN_INFO "Thermostat: high %i.%i, low %i.%i, "
+	       "current %i.%i C, fan %s.\n",
+	       th.hi >> 1, th.hi & 1 ? 5 : 0,
+	       th.lo >> 1, th.lo & 1 ? 5 : 0,
+	       ret   >> 1, ret   & 1 ? 5 : 0,
+	       fan_state[netwinder_get_fan()]);
+
+	return 0;
+}
+
+static void __exit ds1620_exit(void)
+{
+#ifdef THERM_USE_PROC
+	remove_proc_entry("therm", NULL);
+#endif
+	misc_deregister(&ds1620_miscdev);
+}
+
+module_init(ds1620_init);
+module_exit(ds1620_exit);
+
+MODULE_DESCRIPTION("Dallas Semiconductor DS1620 thermometer driver");
+MODULE_LICENSE("GPL");