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, 244 insertions, 0 deletions

diff --git a/drivers/input/joystick/cobra.c b/drivers/input/joystick/cobra.c
new file mode 100644
index 000000000..ffa6d49c8
--- /dev/null
+++ b/drivers/input/joystick/cobra.c
@@ -0,0 +1,244 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 1999-2001 Vojtech Pavlik
+ */
+
+/*
+ * Creative Labs Blaster GamePad Cobra driver for Linux
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/gameport.h>
+#include <linux/input.h>
+#include <linux/jiffies.h>
+
+#define DRIVER_DESC	"Creative Labs Blaster GamePad Cobra driver"
+
+MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+#define COBRA_MAX_STROBE	45	/* 45 us max wait for first strobe */
+#define COBRA_LENGTH		36
+
+static int cobra_btn[] = { BTN_START, BTN_SELECT, BTN_TL, BTN_TR, BTN_X, BTN_Y, BTN_Z, BTN_A, BTN_B, BTN_C, BTN_TL2, BTN_TR2, 0 };
+
+struct cobra {
+	struct gameport *gameport;
+	struct input_dev *dev[2];
+	int reads;
+	int bads;
+	unsigned char exists;
+	char phys[2][32];
+};
+
+static unsigned char cobra_read_packet(struct gameport *gameport, unsigned int *data)
+{
+	unsigned long flags;
+	unsigned char u, v, w;
+	__u64 buf[2];
+	int r[2], t[2];
+	int i, j, ret;
+
+	int strobe = gameport_time(gameport, COBRA_MAX_STROBE);
+
+	for (i = 0; i < 2; i++) {
+		r[i] = buf[i] = 0;
+		t[i] = COBRA_MAX_STROBE;
+	}
+
+	local_irq_save(flags);
+
+	u = gameport_read(gameport);
+
+	do {
+		t[0]--; t[1]--;
+		v = gameport_read(gameport);
+		for (i = 0, w = u ^ v; i < 2 && w; i++, w >>= 2)
+			if (w & 0x30) {
+				if ((w & 0x30) < 0x30 && r[i] < COBRA_LENGTH && t[i] > 0) {
+					buf[i] |= (__u64)((w >> 5) & 1) << r[i]++;
+					t[i] = strobe;
+					u = v;
+				} else t[i] = 0;
+			}
+	} while (t[0] > 0 || t[1] > 0);
+
+	local_irq_restore(flags);
+
+	ret = 0;
+
+	for (i = 0; i < 2; i++) {
+
+		if (r[i] != COBRA_LENGTH) continue;
+
+		for (j = 0; j < COBRA_LENGTH && (buf[i] & 0x04104107f) ^ 0x041041040; j++)
+			buf[i] = (buf[i] >> 1) | ((__u64)(buf[i] & 1) << (COBRA_LENGTH - 1));
+
+		if (j < COBRA_LENGTH) ret |= (1 << i);
+
+		data[i] = ((buf[i] >>  7) & 0x000001f) | ((buf[i] >>  8) & 0x00003e0)
+			| ((buf[i] >>  9) & 0x0007c00) | ((buf[i] >> 10) & 0x00f8000)
+			| ((buf[i] >> 11) & 0x1f00000);
+
+	}
+
+	return ret;
+}
+
+static void cobra_poll(struct gameport *gameport)
+{
+	struct cobra *cobra = gameport_get_drvdata(gameport);
+	struct input_dev *dev;
+	unsigned int data[2];
+	int i, j, r;
+
+	cobra->reads++;
+
+	if ((r = cobra_read_packet(gameport, data)) != cobra->exists) {
+		cobra->bads++;
+		return;
+	}
+
+	for (i = 0; i < 2; i++)
+		if (cobra->exists & r & (1 << i)) {
+
+			dev = cobra->dev[i];
+
+			input_report_abs(dev, ABS_X, ((data[i] >> 4) & 1) - ((data[i] >> 3) & 1));
+			input_report_abs(dev, ABS_Y, ((data[i] >> 2) & 1) - ((data[i] >> 1) & 1));
+
+			for (j = 0; cobra_btn[j]; j++)
+				input_report_key(dev, cobra_btn[j], data[i] & (0x20 << j));
+
+			input_sync(dev);
+
+		}
+}
+
+static int cobra_open(struct input_dev *dev)
+{
+	struct cobra *cobra = input_get_drvdata(dev);
+
+	gameport_start_polling(cobra->gameport);
+	return 0;
+}
+
+static void cobra_close(struct input_dev *dev)
+{
+	struct cobra *cobra = input_get_drvdata(dev);
+
+	gameport_stop_polling(cobra->gameport);
+}
+
+static int cobra_connect(struct gameport *gameport, struct gameport_driver *drv)
+{
+	struct cobra *cobra;
+	struct input_dev *input_dev;
+	unsigned int data[2];
+	int i, j;
+	int err;
+
+	cobra = kzalloc_obj(*cobra);
+	if (!cobra)
+		return -ENOMEM;
+
+	cobra->gameport = gameport;
+
+	gameport_set_drvdata(gameport, cobra);
+
+	err = gameport_open(gameport, drv, GAMEPORT_MODE_RAW);
+	if (err)
+		goto fail1;
+
+	cobra->exists = cobra_read_packet(gameport, data);
+
+	for (i = 0; i < 2; i++)
+		if ((cobra->exists >> i) & data[i] & 1) {
+			printk(KERN_WARNING "cobra.c: Device %d on %s has the Ext bit set. ID is: %d"
+				" Contact vojtech@ucw.cz\n", i, gameport->phys, (data[i] >> 2) & 7);
+			cobra->exists &= ~(1 << i);
+		}
+
+	if (!cobra->exists) {
+		err = -ENODEV;
+		goto fail2;
+	}
+
+	gameport_set_poll_handler(gameport, cobra_poll);
+	gameport_set_poll_interval(gameport, 20);
+
+	for (i = 0; i < 2; i++) {
+		if (~(cobra->exists >> i) & 1)
+			continue;
+
+		cobra->dev[i] = input_dev = input_allocate_device();
+		if (!input_dev) {
+			err = -ENOMEM;
+			goto fail3;
+		}
+
+		snprintf(cobra->phys[i], sizeof(cobra->phys[i]),
+			 "%s/input%d", gameport->phys, i);
+
+		input_dev->name = "Creative Labs Blaster GamePad Cobra";
+		input_dev->phys = cobra->phys[i];
+		input_dev->id.bustype = BUS_GAMEPORT;
+		input_dev->id.vendor = GAMEPORT_ID_VENDOR_CREATIVE;
+		input_dev->id.product = 0x0008;
+		input_dev->id.version = 0x0100;
+		input_dev->dev.parent = &gameport->dev;
+
+		input_set_drvdata(input_dev, cobra);
+
+		input_dev->open = cobra_open;
+		input_dev->close = cobra_close;
+
+		input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+		input_set_abs_params(input_dev, ABS_X, -1, 1, 0, 0);
+		input_set_abs_params(input_dev, ABS_Y, -1, 1, 0, 0);
+		for (j = 0; cobra_btn[j]; j++)
+			set_bit(cobra_btn[j], input_dev->keybit);
+
+		err = input_register_device(cobra->dev[i]);
+		if (err)
+			goto fail4;
+	}
+
+	return 0;
+
+ fail4:	input_free_device(cobra->dev[i]);
+ fail3:	while (--i >= 0)
+		if (cobra->dev[i])
+			input_unregister_device(cobra->dev[i]);
+ fail2:	gameport_close(gameport);
+ fail1:	gameport_set_drvdata(gameport, NULL);
+	kfree(cobra);
+	return err;
+}
+
+static void cobra_disconnect(struct gameport *gameport)
+{
+	struct cobra *cobra = gameport_get_drvdata(gameport);
+	int i;
+
+	for (i = 0; i < 2; i++)
+		if ((cobra->exists >> i) & 1)
+			input_unregister_device(cobra->dev[i]);
+	gameport_close(gameport);
+	gameport_set_drvdata(gameport, NULL);
+	kfree(cobra);
+}
+
+static struct gameport_driver cobra_drv = {
+	.driver		= {
+		.name	= "cobra",
+	},
+	.description	= DRIVER_DESC,
+	.connect	= cobra_connect,
+	.disconnect	= cobra_disconnect,
+};
+
+module_gameport_driver(cobra_drv);