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, 157 insertions, 0 deletions

diff --git a/drivers/input/joystick/amijoy.c b/drivers/input/joystick/amijoy.c
new file mode 100644
index 000000000..3752dc2a2
--- /dev/null
+++ b/drivers/input/joystick/amijoy.c
@@ -0,0 +1,157 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 1998-2001 Vojtech Pavlik
+ */
+
+/*
+ * Driver for Amiga joysticks for Linux/m68k
+ */
+
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/input.h>
+#include <linux/interrupt.h>
+#include <linux/mutex.h>
+
+#include <asm/amigahw.h>
+#include <asm/amigaints.h>
+
+MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
+MODULE_DESCRIPTION("Driver for Amiga joysticks");
+MODULE_LICENSE("GPL");
+
+static int amijoy[2] = { 0, 1 };
+module_param_array_named(map, amijoy, uint, NULL, 0);
+MODULE_PARM_DESC(map, "Map of attached joysticks in form of <a>,<b> (default is 0,1)");
+
+static int amijoy_used;
+static DEFINE_MUTEX(amijoy_mutex);
+static struct input_dev *amijoy_dev[2];
+static char *amijoy_phys[2] = { "amijoy/input0", "amijoy/input1" };
+
+static irqreturn_t amijoy_interrupt(int irq, void *dummy)
+{
+	int i, data = 0, button = 0;
+
+	for (i = 0; i < 2; i++)
+		if (amijoy[i]) {
+
+			switch (i) {
+				case 0: data = ~amiga_custom.joy0dat; button = (~ciaa.pra >> 6) & 1; break;
+				case 1: data = ~amiga_custom.joy1dat; button = (~ciaa.pra >> 7) & 1; break;
+			}
+
+			input_report_key(amijoy_dev[i], BTN_TRIGGER, button);
+
+			input_report_abs(amijoy_dev[i], ABS_X, ((data >> 1) & 1) - ((data >> 9) & 1));
+			data = ~(data ^ (data << 1));
+			input_report_abs(amijoy_dev[i], ABS_Y, ((data >> 1) & 1) - ((data >> 9) & 1));
+
+			input_sync(amijoy_dev[i]);
+		}
+	return IRQ_HANDLED;
+}
+
+static int amijoy_open(struct input_dev *dev)
+{
+	int err;
+
+	err = mutex_lock_interruptible(&amijoy_mutex);
+	if (err)
+		return err;
+
+	if (!amijoy_used && request_irq(IRQ_AMIGA_VERTB, amijoy_interrupt, 0, "amijoy", amijoy_interrupt)) {
+		printk(KERN_ERR "amijoy.c: Can't allocate irq %d\n", IRQ_AMIGA_VERTB);
+		err = -EBUSY;
+		goto out;
+	}
+
+	amijoy_used++;
+out:
+	mutex_unlock(&amijoy_mutex);
+	return err;
+}
+
+static void amijoy_close(struct input_dev *dev)
+{
+	mutex_lock(&amijoy_mutex);
+	if (!--amijoy_used)
+		free_irq(IRQ_AMIGA_VERTB, amijoy_interrupt);
+	mutex_unlock(&amijoy_mutex);
+}
+
+static int __init amijoy_init(void)
+{
+	int i, j;
+	int err;
+
+	if (!MACH_IS_AMIGA)
+		return -ENODEV;
+
+	for (i = 0; i < 2; i++) {
+		if (!amijoy[i])
+			continue;
+
+		amijoy_dev[i] = input_allocate_device();
+		if (!amijoy_dev[i]) {
+			err = -ENOMEM;
+			goto fail;
+		}
+
+		if (!request_mem_region(CUSTOM_PHYSADDR + 10 + i * 2, 2, "amijoy [Denise]")) {
+			input_free_device(amijoy_dev[i]);
+			err = -EBUSY;
+			goto fail;
+		}
+
+		amijoy_dev[i]->name = "Amiga joystick";
+		amijoy_dev[i]->phys = amijoy_phys[i];
+		amijoy_dev[i]->id.bustype = BUS_AMIGA;
+		amijoy_dev[i]->id.vendor = 0x0001;
+		amijoy_dev[i]->id.product = 0x0003;
+		amijoy_dev[i]->id.version = 0x0100;
+
+		amijoy_dev[i]->open = amijoy_open;
+		amijoy_dev[i]->close = amijoy_close;
+
+		amijoy_dev[i]->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+		amijoy_dev[i]->absbit[0] = BIT_MASK(ABS_X) | BIT_MASK(ABS_Y);
+		amijoy_dev[i]->keybit[BIT_WORD(BTN_LEFT)] = BIT_MASK(BTN_LEFT) |
+			BIT_MASK(BTN_MIDDLE) | BIT_MASK(BTN_RIGHT);
+		for (j = 0; j < 2; j++) {
+			input_set_abs_params(amijoy_dev[i], ABS_X + j,
+					     -1, 1, 0, 0);
+		}
+
+		err = input_register_device(amijoy_dev[i]);
+		if (err) {
+			input_free_device(amijoy_dev[i]);
+			goto fail;
+		}
+	}
+	return 0;
+
+ fail:	while (--i >= 0)
+		if (amijoy[i]) {
+			input_unregister_device(amijoy_dev[i]);
+			release_mem_region(CUSTOM_PHYSADDR + 10 + i * 2, 2);
+		}
+	return err;
+}
+
+static void __exit amijoy_exit(void)
+{
+	int i;
+
+	for (i = 0; i < 2; i++)
+		if (amijoy[i]) {
+			input_unregister_device(amijoy_dev[i]);
+			release_mem_region(CUSTOM_PHYSADDR + 10 + i * 2, 2);
+		}
+}
+
+module_init(amijoy_init);
+module_exit(amijoy_exit);