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, 304 insertions, 0 deletions

diff --git a/drivers/input/misc/apanel.c b/drivers/input/misc/apanel.c
new file mode 100644
index 000000000..3eb02a64a
--- /dev/null
+++ b/drivers/input/misc/apanel.c
@@ -0,0 +1,304 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Fujitsu Lifebook Application Panel button drive
+ *
+ *  Copyright (C) 2007 Stephen Hemminger <shemminger@linux-foundation.org>
+ *  Copyright (C) 2001-2003 Jochen Eisinger <jochen@penguin-breeder.org>
+ *
+ * Many Fujitsu Lifebook laptops have a small panel of buttons that are
+ * accessible via the i2c/smbus interface. This driver polls those
+ * buttons and generates input events.
+ *
+ * For more details see:
+ *	http://apanel.sourceforge.net/tech.php
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/ioport.h>
+#include <linux/io.h>
+#include <linux/input.h>
+#include <linux/i2c.h>
+#include <linux/leds.h>
+
+#define APANEL_NAME	"Fujitsu Application Panel"
+#define APANEL		"apanel"
+
+/* How often we poll keys - msecs */
+#define POLL_INTERVAL_DEFAULT	1000
+
+/* Magic constants in BIOS that tell about buttons */
+enum apanel_devid {
+	APANEL_DEV_NONE	  = 0,
+	APANEL_DEV_APPBTN = 1,
+	APANEL_DEV_CDBTN  = 2,
+	APANEL_DEV_LCD	  = 3,
+	APANEL_DEV_LED	  = 4,
+
+	APANEL_DEV_MAX,
+};
+
+enum apanel_chip {
+	CHIP_NONE    = 0,
+	CHIP_OZ992C  = 1,
+	CHIP_OZ163T  = 2,
+	CHIP_OZ711M3 = 4,
+};
+
+/* Result of BIOS snooping/probing -- what features are supported */
+static enum apanel_chip device_chip[APANEL_DEV_MAX];
+
+#define MAX_PANEL_KEYS	12
+
+struct apanel {
+	struct input_dev *idev;
+	struct i2c_client *client;
+	unsigned short keymap[MAX_PANEL_KEYS];
+	u16 nkeys;
+	struct led_classdev mail_led;
+};
+
+static const unsigned short apanel_keymap[MAX_PANEL_KEYS] = {
+	[0] = KEY_MAIL,
+	[1] = KEY_WWW,
+	[2] = KEY_PROG2,
+	[3] = KEY_PROG1,
+
+	[8] = KEY_FORWARD,
+	[9] = KEY_REWIND,
+	[10] = KEY_STOPCD,
+	[11] = KEY_PLAYPAUSE,
+};
+
+static void report_key(struct input_dev *input, unsigned keycode)
+{
+	dev_dbg(input->dev.parent, "report key %#x\n", keycode);
+	input_report_key(input, keycode, 1);
+	input_sync(input);
+
+	input_report_key(input, keycode, 0);
+	input_sync(input);
+}
+
+/* Poll for key changes
+ *
+ * Read Application keys via SMI
+ *  A (0x4), B (0x8), Internet (0x2), Email (0x1).
+ *
+ * CD keys:
+ * Forward (0x100), Rewind (0x200), Stop (0x400), Pause (0x800)
+ */
+static void apanel_poll(struct input_dev *idev)
+{
+	struct apanel *ap = input_get_drvdata(idev);
+	u8 cmd = device_chip[APANEL_DEV_APPBTN] == CHIP_OZ992C ? 0 : 8;
+	s32 data;
+	int i;
+
+	data = i2c_smbus_read_word_data(ap->client, cmd);
+	if (data < 0)
+		return;	/* ignore errors (due to ACPI??) */
+
+	/* write back to clear latch */
+	i2c_smbus_write_word_data(ap->client, cmd, 0);
+
+	if (!data)
+		return;
+
+	dev_dbg(&idev->dev, APANEL ": data %#x\n", data);
+	for (i = 0; i < idev->keycodemax; i++)
+		if ((1u << i) & data)
+			report_key(idev, ap->keymap[i]);
+}
+
+static int mail_led_set(struct led_classdev *led,
+			 enum led_brightness value)
+{
+	struct apanel *ap = container_of(led, struct apanel, mail_led);
+	u16 led_bits = value != LED_OFF ? 0x8000 : 0x0000;
+
+	return i2c_smbus_write_word_data(ap->client, 0x10, led_bits);
+}
+
+static int apanel_probe(struct i2c_client *client)
+{
+	struct apanel *ap;
+	struct input_dev *idev;
+	u8 cmd = device_chip[APANEL_DEV_APPBTN] == CHIP_OZ992C ? 0 : 8;
+	int i, err;
+
+	ap = devm_kzalloc(&client->dev, sizeof(*ap), GFP_KERNEL);
+	if (!ap)
+		return -ENOMEM;
+
+	idev = devm_input_allocate_device(&client->dev);
+	if (!idev)
+		return -ENOMEM;
+
+	ap->idev = idev;
+	ap->client = client;
+
+	i2c_set_clientdata(client, ap);
+
+	err = i2c_smbus_write_word_data(client, cmd, 0);
+	if (err) {
+		dev_warn(&client->dev, "smbus write error %d\n", err);
+		return err;
+	}
+
+	input_set_drvdata(idev, ap);
+
+	idev->name = APANEL_NAME " buttons";
+	idev->phys = "apanel/input0";
+	idev->id.bustype = BUS_HOST;
+
+	memcpy(ap->keymap, apanel_keymap, sizeof(apanel_keymap));
+	idev->keycode = ap->keymap;
+	idev->keycodesize = sizeof(ap->keymap[0]);
+	idev->keycodemax = (device_chip[APANEL_DEV_CDBTN] != CHIP_NONE) ? 12 : 4;
+
+	set_bit(EV_KEY, idev->evbit);
+	for (i = 0; i < idev->keycodemax; i++)
+		if (ap->keymap[i])
+			set_bit(ap->keymap[i], idev->keybit);
+
+	err = input_setup_polling(idev, apanel_poll);
+	if (err)
+		return err;
+
+	input_set_poll_interval(idev, POLL_INTERVAL_DEFAULT);
+
+	err = input_register_device(idev);
+	if (err)
+		return err;
+
+	if (device_chip[APANEL_DEV_LED] != CHIP_NONE) {
+		ap->mail_led.name = "mail:blue";
+		ap->mail_led.brightness_set_blocking = mail_led_set;
+		err = devm_led_classdev_register(&client->dev, &ap->mail_led);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+static void apanel_shutdown(struct i2c_client *client)
+{
+	struct apanel *ap = i2c_get_clientdata(client);
+
+	if (device_chip[APANEL_DEV_LED] != CHIP_NONE)
+		led_set_brightness(&ap->mail_led, LED_OFF);
+}
+
+static const struct i2c_device_id apanel_id[] = {
+	{ .name = "fujitsu_apanel" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, apanel_id);
+
+static struct i2c_driver apanel_driver = {
+	.driver = {
+		.name = APANEL,
+	},
+	.probe		= apanel_probe,
+	.shutdown	= apanel_shutdown,
+	.id_table	= apanel_id,
+};
+
+/* Scan the system ROM for the signature "FJKEYINF" */
+static __init const void __iomem *bios_signature(const void __iomem *bios)
+{
+	ssize_t offset;
+	const unsigned char signature[] = "FJKEYINF";
+
+	for (offset = 0; offset < 0x10000; offset += 0x10) {
+		if (check_signature(bios + offset, signature,
+				    sizeof(signature)-1))
+			return bios + offset;
+	}
+	pr_notice(APANEL ": Fujitsu BIOS signature '%s' not found...\n",
+		  signature);
+	return NULL;
+}
+
+static int __init apanel_init(void)
+{
+	void __iomem *bios;
+	const void __iomem *p;
+	u8 devno;
+	unsigned char i2c_addr;
+	int found = 0;
+
+	bios = ioremap(0xF0000, 0x10000); /* Can't fail */
+
+	p = bios_signature(bios);
+	if (!p) {
+		iounmap(bios);
+		return -ENODEV;
+	}
+
+	/* just use the first address */
+	p += 8;
+	i2c_addr = readb(p + 3) >> 1;
+
+	for ( ; (devno = readb(p)) & 0x7f; p += 4) {
+		unsigned char method, slave, chip;
+
+		method = readb(p + 1);
+		chip = readb(p + 2);
+		slave = readb(p + 3) >> 1;
+
+		if (slave != i2c_addr) {
+			pr_notice(APANEL ": only one SMBus slave "
+				  "address supported, skipping device...\n");
+			continue;
+		}
+
+		/* translate alternative device numbers */
+		switch (devno) {
+		case 6:
+			devno = APANEL_DEV_APPBTN;
+			break;
+		case 7:
+			devno = APANEL_DEV_LED;
+			break;
+		}
+
+		if (devno >= APANEL_DEV_MAX)
+			pr_notice(APANEL ": unknown device %u found\n", devno);
+		else if (device_chip[devno] != CHIP_NONE)
+			pr_warn(APANEL ": duplicate entry for devno %u\n",
+				devno);
+
+		else if (method != 1 && method != 2 && method != 4) {
+			pr_notice(APANEL ": unknown method %u for devno %u\n",
+				  method, devno);
+		} else {
+			device_chip[devno] = (enum apanel_chip) chip;
+			++found;
+		}
+	}
+	iounmap(bios);
+
+	if (found == 0) {
+		pr_info(APANEL ": no input devices reported by BIOS\n");
+		return -EIO;
+	}
+
+	return i2c_add_driver(&apanel_driver);
+}
+module_init(apanel_init);
+
+static void __exit apanel_cleanup(void)
+{
+	i2c_del_driver(&apanel_driver);
+}
+module_exit(apanel_cleanup);
+
+MODULE_AUTHOR("Stephen Hemminger <shemminger@linux-foundation.org>");
+MODULE_DESCRIPTION(APANEL_NAME " driver");
+MODULE_LICENSE("GPL");
+
+MODULE_ALIAS("dmi:*:svnFUJITSU:pnLifeBook*:pvr*:rvnFUJITSU:*");
+MODULE_ALIAS("dmi:*:svnFUJITSU:pnLifebook*:pvr*:rvnFUJITSU:*");