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, 342 insertions, 0 deletions

diff --git a/drivers/input/joystick/n64joy.c b/drivers/input/joystick/n64joy.c
new file mode 100644
index 000000000..43a02bb99
--- /dev/null
+++ b/drivers/input/joystick/n64joy.c
@@ -0,0 +1,342 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Support for the four N64 controllers.
+ *
+ * Copyright (c) 2021 Lauri Kasanen
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/input.h>
+#include <linux/limits.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/timer.h>
+
+MODULE_AUTHOR("Lauri Kasanen <cand@gmx.com>");
+MODULE_DESCRIPTION("Driver for N64 controllers");
+MODULE_LICENSE("GPL");
+
+#define PIF_RAM 0x1fc007c0
+
+#define SI_DRAM_REG 0
+#define SI_READ_REG 1
+#define SI_WRITE_REG 4
+#define SI_STATUS_REG 6
+
+#define SI_STATUS_DMA_BUSY  BIT(0)
+#define SI_STATUS_IO_BUSY   BIT(1)
+
+#define N64_CONTROLLER_ID 0x0500
+
+#define MAX_CONTROLLERS 4
+
+static const char *n64joy_phys[MAX_CONTROLLERS] = {
+	"n64joy/port0",
+	"n64joy/port1",
+	"n64joy/port2",
+	"n64joy/port3",
+};
+
+struct n64joy_priv {
+	u64 si_buf[8] ____cacheline_aligned;
+	struct timer_list timer;
+	struct mutex n64joy_mutex;
+	struct input_dev *n64joy_dev[MAX_CONTROLLERS];
+	u32 __iomem *reg_base;
+	u8 n64joy_opened;
+};
+
+struct joydata {
+	unsigned int: 16; /* unused */
+	unsigned int err: 2;
+	unsigned int: 14; /* unused */
+
+	union {
+		u32 data;
+
+		struct {
+			unsigned int a: 1;
+			unsigned int b: 1;
+			unsigned int z: 1;
+			unsigned int start: 1;
+			unsigned int up: 1;
+			unsigned int down: 1;
+			unsigned int left: 1;
+			unsigned int right: 1;
+			unsigned int: 2; /* unused */
+			unsigned int l: 1;
+			unsigned int r: 1;
+			unsigned int c_up: 1;
+			unsigned int c_down: 1;
+			unsigned int c_left: 1;
+			unsigned int c_right: 1;
+			signed int x: 8;
+			signed int y: 8;
+		};
+	};
+};
+
+static void n64joy_write_reg(u32 __iomem *reg_base, const u8 reg, const u32 value)
+{
+	writel(value, reg_base + reg);
+}
+
+static u32 n64joy_read_reg(u32 __iomem *reg_base, const u8 reg)
+{
+	return readl(reg_base + reg);
+}
+
+static void n64joy_wait_si_dma(u32 __iomem *reg_base)
+{
+	while (n64joy_read_reg(reg_base, SI_STATUS_REG) &
+	       (SI_STATUS_DMA_BUSY | SI_STATUS_IO_BUSY))
+		cpu_relax();
+}
+
+static void n64joy_exec_pif(struct n64joy_priv *priv, const u64 in[8])
+{
+	unsigned long flags;
+
+	dma_cache_wback_inv((unsigned long) in, 8 * 8);
+	dma_cache_inv((unsigned long) priv->si_buf, 8 * 8);
+
+	local_irq_save(flags);
+
+	n64joy_wait_si_dma(priv->reg_base);
+
+	barrier();
+	n64joy_write_reg(priv->reg_base, SI_DRAM_REG, virt_to_phys(in));
+	barrier();
+	n64joy_write_reg(priv->reg_base, SI_WRITE_REG, PIF_RAM);
+	barrier();
+
+	n64joy_wait_si_dma(priv->reg_base);
+
+	barrier();
+	n64joy_write_reg(priv->reg_base, SI_DRAM_REG, virt_to_phys(priv->si_buf));
+	barrier();
+	n64joy_write_reg(priv->reg_base, SI_READ_REG, PIF_RAM);
+	barrier();
+
+	n64joy_wait_si_dma(priv->reg_base);
+
+	local_irq_restore(flags);
+}
+
+static const u64 polldata[] ____cacheline_aligned = {
+	0xff010401ffffffff,
+	0xff010401ffffffff,
+	0xff010401ffffffff,
+	0xff010401ffffffff,
+	0xfe00000000000000,
+	0,
+	0,
+	1
+};
+
+static void n64joy_poll(struct timer_list *t)
+{
+	const struct joydata *data;
+	struct n64joy_priv *priv = container_of(t, struct n64joy_priv, timer);
+	struct input_dev *dev;
+	u32 i;
+
+	n64joy_exec_pif(priv, polldata);
+
+	data = (struct joydata *) priv->si_buf;
+
+	for (i = 0; i < MAX_CONTROLLERS; i++) {
+		if (!priv->n64joy_dev[i])
+			continue;
+
+		dev = priv->n64joy_dev[i];
+
+		/* d-pad */
+		input_report_key(dev, BTN_DPAD_UP, data[i].up);
+		input_report_key(dev, BTN_DPAD_DOWN, data[i].down);
+		input_report_key(dev, BTN_DPAD_LEFT, data[i].left);
+		input_report_key(dev, BTN_DPAD_RIGHT, data[i].right);
+
+		/* c buttons */
+		input_report_key(dev, BTN_FORWARD, data[i].c_up);
+		input_report_key(dev, BTN_BACK, data[i].c_down);
+		input_report_key(dev, BTN_LEFT, data[i].c_left);
+		input_report_key(dev, BTN_RIGHT, data[i].c_right);
+
+		/* matching buttons */
+		input_report_key(dev, BTN_START, data[i].start);
+		input_report_key(dev, BTN_Z, data[i].z);
+
+		/* remaining ones: a, b, l, r */
+		input_report_key(dev, BTN_0, data[i].a);
+		input_report_key(dev, BTN_1, data[i].b);
+		input_report_key(dev, BTN_2, data[i].l);
+		input_report_key(dev, BTN_3, data[i].r);
+
+		input_report_abs(dev, ABS_X, data[i].x);
+		input_report_abs(dev, ABS_Y, data[i].y);
+
+		input_sync(dev);
+	}
+
+	mod_timer(&priv->timer, jiffies + msecs_to_jiffies(16));
+}
+
+static int n64joy_open(struct input_dev *dev)
+{
+	struct n64joy_priv *priv = input_get_drvdata(dev);
+
+	scoped_guard(mutex_intr, &priv->n64joy_mutex) {
+		if (!priv->n64joy_opened) {
+			/*
+			 * We could use the vblank irq, but it's not important
+			 * if the poll point slightly changes.
+			 */
+			timer_setup(&priv->timer, n64joy_poll, 0);
+			mod_timer(&priv->timer, jiffies + msecs_to_jiffies(16));
+		}
+
+		priv->n64joy_opened++;
+		return 0;
+	}
+
+	return -EINTR;
+}
+
+static void n64joy_close(struct input_dev *dev)
+{
+	struct n64joy_priv *priv = input_get_drvdata(dev);
+
+	guard(mutex)(&priv->n64joy_mutex);
+
+	if (!--priv->n64joy_opened)
+		timer_delete_sync(&priv->timer);
+}
+
+static const u64 __initconst scandata[] ____cacheline_aligned = {
+	0xff010300ffffffff,
+	0xff010300ffffffff,
+	0xff010300ffffffff,
+	0xff010300ffffffff,
+	0xfe00000000000000,
+	0,
+	0,
+	1
+};
+
+/*
+ * The target device is embedded and RAM-constrained. We save RAM
+ * by initializing in __init code that gets dropped late in boot.
+ * For the same reason there is no module or unloading support.
+ */
+static int __init n64joy_probe(struct platform_device *pdev)
+{
+	const struct joydata *data;
+	struct n64joy_priv *priv;
+	struct input_dev *dev;
+	int err = 0;
+	u32 i, j, found = 0;
+
+	priv = kzalloc_obj(*priv);
+	if (!priv)
+		return -ENOMEM;
+	mutex_init(&priv->n64joy_mutex);
+
+	priv->reg_base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(priv->reg_base)) {
+		err = PTR_ERR(priv->reg_base);
+		goto fail;
+	}
+
+	/* The controllers are not hotpluggable, so we can scan in init */
+	n64joy_exec_pif(priv, scandata);
+
+	data = (struct joydata *) priv->si_buf;
+
+	for (i = 0; i < MAX_CONTROLLERS; i++) {
+		if (!data[i].err && data[i].data >> 16 == N64_CONTROLLER_ID) {
+			found++;
+
+			dev = priv->n64joy_dev[i] = input_allocate_device();
+			if (!priv->n64joy_dev[i]) {
+				err = -ENOMEM;
+				goto fail;
+			}
+
+			input_set_drvdata(dev, priv);
+
+			dev->name = "N64 controller";
+			dev->phys = n64joy_phys[i];
+			dev->id.bustype = BUS_HOST;
+			dev->id.vendor = 0;
+			dev->id.product = data[i].data >> 16;
+			dev->id.version = 0;
+			dev->dev.parent = &pdev->dev;
+
+			dev->open = n64joy_open;
+			dev->close = n64joy_close;
+
+			/* d-pad */
+			input_set_capability(dev, EV_KEY, BTN_DPAD_UP);
+			input_set_capability(dev, EV_KEY, BTN_DPAD_DOWN);
+			input_set_capability(dev, EV_KEY, BTN_DPAD_LEFT);
+			input_set_capability(dev, EV_KEY, BTN_DPAD_RIGHT);
+			/* c buttons */
+			input_set_capability(dev, EV_KEY, BTN_LEFT);
+			input_set_capability(dev, EV_KEY, BTN_RIGHT);
+			input_set_capability(dev, EV_KEY, BTN_FORWARD);
+			input_set_capability(dev, EV_KEY, BTN_BACK);
+			/* matching buttons */
+			input_set_capability(dev, EV_KEY, BTN_START);
+			input_set_capability(dev, EV_KEY, BTN_Z);
+			/* remaining ones: a, b, l, r */
+			input_set_capability(dev, EV_KEY, BTN_0);
+			input_set_capability(dev, EV_KEY, BTN_1);
+			input_set_capability(dev, EV_KEY, BTN_2);
+			input_set_capability(dev, EV_KEY, BTN_3);
+
+			for (j = 0; j < 2; j++)
+				input_set_abs_params(dev, ABS_X + j,
+						     S8_MIN, S8_MAX, 0, 0);
+
+			err = input_register_device(dev);
+			if (err) {
+				input_free_device(dev);
+				goto fail;
+			}
+		}
+	}
+
+	pr_info("%u controller(s) connected\n", found);
+
+	if (!found)
+		return -ENODEV;
+
+	return 0;
+fail:
+	for (i = 0; i < MAX_CONTROLLERS; i++) {
+		if (!priv->n64joy_dev[i])
+			continue;
+		input_unregister_device(priv->n64joy_dev[i]);
+	}
+	return err;
+}
+
+static struct platform_driver n64joy_driver = {
+	.driver = {
+		.name = "n64joy",
+	},
+};
+
+static int __init n64joy_init(void)
+{
+	return platform_driver_probe(&n64joy_driver, n64joy_probe);
+}
+
+module_init(n64joy_init);