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, 242 insertions, 0 deletions

diff --git a/drivers/input/keyboard/amikbd.c b/drivers/input/keyboard/amikbd.c
new file mode 100644
index 000000000..ecfae0b0b
--- /dev/null
+++ b/drivers/input/keyboard/amikbd.c
@@ -0,0 +1,242 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2000-2001 Vojtech Pavlik
+ *
+ *  Based on the work of:
+ *	Hamish Macdonald
+ */
+
+/*
+ * Amiga keyboard driver for Linux/m68k
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/input.h>
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+#include <linux/keyboard.h>
+#include <linux/platform_device.h>
+
+#include <asm/amigaints.h>
+#include <asm/amigahw.h>
+#include <asm/irq.h>
+
+MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
+MODULE_DESCRIPTION("Amiga keyboard driver");
+MODULE_LICENSE("GPL");
+
+#ifdef CONFIG_VT
+static unsigned char amikbd_keycode[0x78] __initdata = {
+	[0]	 = KEY_GRAVE,
+	[1]	 = KEY_1,
+	[2]	 = KEY_2,
+	[3]	 = KEY_3,
+	[4]	 = KEY_4,
+	[5]	 = KEY_5,
+	[6]	 = KEY_6,
+	[7]	 = KEY_7,
+	[8]	 = KEY_8,
+	[9]	 = KEY_9,
+	[10]	 = KEY_0,
+	[11]	 = KEY_MINUS,
+	[12]	 = KEY_EQUAL,
+	[13]	 = KEY_BACKSLASH,
+	[15]	 = KEY_KP0,
+	[16]	 = KEY_Q,
+	[17]	 = KEY_W,
+	[18]	 = KEY_E,
+	[19]	 = KEY_R,
+	[20]	 = KEY_T,
+	[21]	 = KEY_Y,
+	[22]	 = KEY_U,
+	[23]	 = KEY_I,
+	[24]	 = KEY_O,
+	[25]	 = KEY_P,
+	[26]	 = KEY_LEFTBRACE,
+	[27]	 = KEY_RIGHTBRACE,
+	[29]	 = KEY_KP1,
+	[30]	 = KEY_KP2,
+	[31]	 = KEY_KP3,
+	[32]	 = KEY_A,
+	[33]	 = KEY_S,
+	[34]	 = KEY_D,
+	[35]	 = KEY_F,
+	[36]	 = KEY_G,
+	[37]	 = KEY_H,
+	[38]	 = KEY_J,
+	[39]	 = KEY_K,
+	[40]	 = KEY_L,
+	[41]	 = KEY_SEMICOLON,
+	[42]	 = KEY_APOSTROPHE,
+	[43]	 = KEY_BACKSLASH,
+	[45]	 = KEY_KP4,
+	[46]	 = KEY_KP5,
+	[47]	 = KEY_KP6,
+	[48]	 = KEY_102ND,
+	[49]	 = KEY_Z,
+	[50]	 = KEY_X,
+	[51]	 = KEY_C,
+	[52]	 = KEY_V,
+	[53]	 = KEY_B,
+	[54]	 = KEY_N,
+	[55]	 = KEY_M,
+	[56]	 = KEY_COMMA,
+	[57]	 = KEY_DOT,
+	[58]	 = KEY_SLASH,
+	[60]	 = KEY_KPDOT,
+	[61]	 = KEY_KP7,
+	[62]	 = KEY_KP8,
+	[63]	 = KEY_KP9,
+	[64]	 = KEY_SPACE,
+	[65]	 = KEY_BACKSPACE,
+	[66]	 = KEY_TAB,
+	[67]	 = KEY_KPENTER,
+	[68]	 = KEY_ENTER,
+	[69]	 = KEY_ESC,
+	[70]	 = KEY_DELETE,
+	[74]	 = KEY_KPMINUS,
+	[76]	 = KEY_UP,
+	[77]	 = KEY_DOWN,
+	[78]	 = KEY_RIGHT,
+	[79]	 = KEY_LEFT,
+	[80]	 = KEY_F1,
+	[81]	 = KEY_F2,
+	[82]	 = KEY_F3,
+	[83]	 = KEY_F4,
+	[84]	 = KEY_F5,
+	[85]	 = KEY_F6,
+	[86]	 = KEY_F7,
+	[87]	 = KEY_F8,
+	[88]	 = KEY_F9,
+	[89]	 = KEY_F10,
+	[90]	 = KEY_KPLEFTPAREN,
+	[91]	 = KEY_KPRIGHTPAREN,
+	[92]	 = KEY_KPSLASH,
+	[93]	 = KEY_KPASTERISK,
+	[94]	 = KEY_KPPLUS,
+	[95]	 = KEY_HELP,
+	[96]	 = KEY_LEFTSHIFT,
+	[97]	 = KEY_RIGHTSHIFT,
+	[98]	 = KEY_CAPSLOCK,
+	[99]	 = KEY_LEFTCTRL,
+	[100]	 = KEY_LEFTALT,
+	[101]	 = KEY_RIGHTALT,
+	[102]	 = KEY_LEFTMETA,
+	[103]	 = KEY_RIGHTMETA
+};
+
+static void __init amikbd_init_console_keymaps(void)
+{
+	/* We can spare 512 bytes on stack for temp_map in init path. */
+	unsigned short temp_map[NR_KEYS];
+	int i, j;
+
+	for (i = 0; i < MAX_NR_KEYMAPS; i++) {
+		if (!key_maps[i])
+			continue;
+		memset(temp_map, 0, sizeof(temp_map));
+		for (j = 0; j < 0x78; j++) {
+			if (!amikbd_keycode[j])
+				continue;
+			temp_map[j] = key_maps[i][amikbd_keycode[j]];
+		}
+		for (j = 0; j < NR_KEYS; j++) {
+			if (!temp_map[j])
+				temp_map[j] = 0xf200;
+		}
+		memcpy(key_maps[i], temp_map, sizeof(temp_map));
+	}
+}
+#else /* !CONFIG_VT */
+static inline void amikbd_init_console_keymaps(void) {}
+#endif /* !CONFIG_VT */
+
+static const char *amikbd_messages[8] = {
+	[0] = KERN_ALERT "amikbd: Ctrl-Amiga-Amiga reset warning!!\n",
+	[1] = KERN_WARNING "amikbd: keyboard lost sync\n",
+	[2] = KERN_WARNING "amikbd: keyboard buffer overflow\n",
+	[3] = KERN_WARNING "amikbd: keyboard controller failure\n",
+	[4] = KERN_ERR "amikbd: keyboard selftest failure\n",
+	[5] = KERN_INFO "amikbd: initiate power-up key stream\n",
+	[6] = KERN_INFO "amikbd: terminate power-up key stream\n",
+	[7] = KERN_WARNING "amikbd: keyboard interrupt\n"
+};
+
+static irqreturn_t amikbd_interrupt(int irq, void *data)
+{
+	struct input_dev *dev = data;
+	unsigned char scancode, down;
+
+	scancode = ~ciaa.sdr;		/* get and invert scancode (keyboard is active low) */
+	ciaa.cra |= 0x40;		/* switch SP pin to output for handshake */
+	udelay(85);			/* wait until 85 us have expired */
+	ciaa.cra &= ~0x40;		/* switch CIA serial port to input mode */
+
+	down = !(scancode & 1);		/* lowest bit is release bit */
+	scancode >>= 1;
+
+	if (scancode < 0x78) {		/* scancodes < 0x78 are keys */
+		if (scancode == 98) {	/* CapsLock is a toggle switch key on Amiga */
+			input_report_key(dev, scancode, 1);
+			input_report_key(dev, scancode, 0);
+		} else {
+			input_report_key(dev, scancode, down);
+		}
+
+		input_sync(dev);
+	} else				/* scancodes >= 0x78 are error codes */
+		printk(amikbd_messages[scancode - 0x78]);
+
+	return IRQ_HANDLED;
+}
+
+static int __init amikbd_probe(struct platform_device *pdev)
+{
+	struct input_dev *dev;
+	int i, err;
+
+	dev = devm_input_allocate_device(&pdev->dev);
+	if (!dev) {
+		dev_err(&pdev->dev, "Not enough memory for input device\n");
+		return -ENOMEM;
+	}
+
+	dev->name = pdev->name;
+	dev->phys = "amikbd/input0";
+	dev->id.bustype = BUS_AMIGA;
+	dev->id.vendor = 0x0001;
+	dev->id.product = 0x0001;
+	dev->id.version = 0x0100;
+
+	dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_REP);
+
+	for (i = 0; i < 0x78; i++)
+		set_bit(i, dev->keybit);
+
+	amikbd_init_console_keymaps();
+
+	ciaa.cra &= ~0x41;	 /* serial data in, turn off TA */
+	err = devm_request_irq(&pdev->dev, IRQ_AMIGA_CIAA_SP, amikbd_interrupt,
+			       0, "amikbd", dev);
+	if (err)
+		return err;
+
+	err = input_register_device(dev);
+	if (err)
+		return err;
+
+	platform_set_drvdata(pdev, dev);
+
+	return 0;
+}
+
+static struct platform_driver amikbd_driver = {
+	.driver   = {
+		.name	= "amiga-keyboard",
+	},
+};
+
+module_platform_driver_probe(amikbd_driver, amikbd_probe);
+
+MODULE_ALIAS("platform:amiga-keyboard");