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, 272 insertions, 0 deletions

diff --git a/drivers/gpio/gpio-syscon.c b/drivers/gpio/gpio-syscon.c
new file mode 100644
index 000000000..40064d4cf
--- /dev/null
+++ b/drivers/gpio/gpio-syscon.c
@@ -0,0 +1,272 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  SYSCON GPIO driver
+ *
+ *  Copyright (C) 2014 Alexander Shiyan <shc_work@mail.ru>
+ */
+
+#include <linux/err.h>
+#include <linux/gpio/driver.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/mfd/syscon.h>
+
+#define GPIO_SYSCON_FEAT_IN	BIT(0)
+#define GPIO_SYSCON_FEAT_OUT	BIT(1)
+#define GPIO_SYSCON_FEAT_DIR	BIT(2)
+
+/* SYSCON driver is designed to use 32-bit wide registers */
+#define SYSCON_REG_SIZE		(4)
+#define SYSCON_REG_BITS		(SYSCON_REG_SIZE * 8)
+
+/**
+ * struct syscon_gpio_data - Configuration for the device.
+ * @flags:		Set of GPIO_SYSCON_FEAT_ flags:
+ *			GPIO_SYSCON_FEAT_IN:	GPIOs supports input,
+ *			GPIO_SYSCON_FEAT_OUT:	GPIOs supports output,
+ *			GPIO_SYSCON_FEAT_DIR:	GPIOs supports switch direction.
+ * @bit_count:		Number of bits used as GPIOs.
+ * @dat_bit_offset:	Offset (in bits) to the first GPIO bit.
+ * @dir_bit_offset:	Optional offset (in bits) to the first bit to switch
+ *			GPIO direction (Used with GPIO_SYSCON_FEAT_DIR flag).
+ * @set:		HW specific callback to assigns output value
+ *			for signal "offset"
+ */
+
+struct syscon_gpio_data {
+	unsigned int	flags;
+	unsigned int	bit_count;
+	unsigned int	dat_bit_offset;
+	unsigned int	dir_bit_offset;
+	int		(*set)(struct gpio_chip *chip, unsigned int offset,
+			       int value);
+};
+
+struct syscon_gpio_priv {
+	struct gpio_chip		chip;
+	struct regmap			*syscon;
+	const struct syscon_gpio_data	*data;
+	u32				dreg_offset;
+	u32				dir_reg_offset;
+};
+
+static int syscon_gpio_get(struct gpio_chip *chip, unsigned offset)
+{
+	struct syscon_gpio_priv *priv = gpiochip_get_data(chip);
+	unsigned int val, offs;
+	int ret;
+
+	offs = priv->dreg_offset + priv->data->dat_bit_offset + offset;
+
+	ret = regmap_read(priv->syscon,
+			  (offs / SYSCON_REG_BITS) * SYSCON_REG_SIZE, &val);
+	if (ret)
+		return ret;
+
+	return !!(val & BIT(offs % SYSCON_REG_BITS));
+}
+
+static int syscon_gpio_set(struct gpio_chip *chip, unsigned int offset, int val)
+{
+	struct syscon_gpio_priv *priv = gpiochip_get_data(chip);
+	unsigned int offs;
+
+	offs = priv->dreg_offset + priv->data->dat_bit_offset + offset;
+
+	return regmap_update_bits(priv->syscon,
+				  (offs / SYSCON_REG_BITS) * SYSCON_REG_SIZE,
+				  BIT(offs % SYSCON_REG_BITS),
+				  val ? BIT(offs % SYSCON_REG_BITS) : 0);
+}
+
+static int syscon_gpio_dir_in(struct gpio_chip *chip, unsigned offset)
+{
+	struct syscon_gpio_priv *priv = gpiochip_get_data(chip);
+
+	if (priv->data->flags & GPIO_SYSCON_FEAT_DIR) {
+		unsigned int offs;
+
+		offs = priv->dir_reg_offset +
+		       priv->data->dir_bit_offset + offset;
+
+		regmap_update_bits(priv->syscon,
+				   (offs / SYSCON_REG_BITS) * SYSCON_REG_SIZE,
+				   BIT(offs % SYSCON_REG_BITS), 0);
+	}
+
+	return 0;
+}
+
+static int syscon_gpio_dir_out(struct gpio_chip *chip, unsigned offset, int val)
+{
+	struct syscon_gpio_priv *priv = gpiochip_get_data(chip);
+
+	if (priv->data->flags & GPIO_SYSCON_FEAT_DIR) {
+		unsigned int offs;
+
+		offs = priv->dir_reg_offset +
+		       priv->data->dir_bit_offset + offset;
+
+		regmap_update_bits(priv->syscon,
+				   (offs / SYSCON_REG_BITS) * SYSCON_REG_SIZE,
+				   BIT(offs % SYSCON_REG_BITS),
+				   BIT(offs % SYSCON_REG_BITS));
+	}
+
+	return chip->set(chip, offset, val);
+}
+
+static const struct syscon_gpio_data clps711x_mctrl_gpio = {
+	/* ARM CLPS711X SYSFLG1 Bits 8-10 */
+	.flags		= GPIO_SYSCON_FEAT_IN,
+	.bit_count	= 3,
+	.dat_bit_offset	= 0x40 * 8 + 8,
+};
+
+static int rockchip_gpio_set(struct gpio_chip *chip, unsigned int offset,
+			     int val)
+{
+	struct syscon_gpio_priv *priv = gpiochip_get_data(chip);
+	unsigned int offs;
+	u8 bit;
+	u32 data;
+	int ret;
+
+	offs = priv->dreg_offset + priv->data->dat_bit_offset + offset;
+	bit = offs % SYSCON_REG_BITS;
+	data = (val ? BIT(bit) : 0) | BIT(bit + 16);
+	ret = regmap_write(priv->syscon,
+			   (offs / SYSCON_REG_BITS) * SYSCON_REG_SIZE,
+			   data);
+	if (ret < 0)
+		dev_err(chip->parent, "gpio write failed ret(%d)\n", ret);
+
+	return ret;
+}
+
+static const struct syscon_gpio_data rockchip_rk3328_gpio_mute = {
+	/* RK3328 GPIO_MUTE is an output only pin at GRF_SOC_CON10[1] */
+	.flags		= GPIO_SYSCON_FEAT_OUT,
+	.bit_count	= 1,
+	.dat_bit_offset = 0x0428 * 8 + 1,
+	.set		= rockchip_gpio_set,
+};
+
+#define KEYSTONE_LOCK_BIT BIT(0)
+
+static int keystone_gpio_set(struct gpio_chip *chip, unsigned int offset,
+			     int val)
+{
+	struct syscon_gpio_priv *priv = gpiochip_get_data(chip);
+	unsigned int offs;
+	int ret;
+
+	offs = priv->dreg_offset + priv->data->dat_bit_offset + offset;
+
+	if (!val)
+		return 0;
+
+	ret = regmap_update_bits(
+			priv->syscon,
+			(offs / SYSCON_REG_BITS) * SYSCON_REG_SIZE,
+			BIT(offs % SYSCON_REG_BITS) | KEYSTONE_LOCK_BIT,
+			BIT(offs % SYSCON_REG_BITS) | KEYSTONE_LOCK_BIT);
+	if (ret < 0)
+		dev_err(chip->parent, "gpio write failed ret(%d)\n", ret);
+
+	return ret;
+}
+
+static const struct syscon_gpio_data keystone_dsp_gpio = {
+	/* ARM Keystone 2 */
+	.flags		= GPIO_SYSCON_FEAT_OUT,
+	.bit_count	= 28,
+	.dat_bit_offset	= 4,
+	.set		= keystone_gpio_set,
+};
+
+static const struct of_device_id syscon_gpio_ids[] = {
+	{
+		.compatible	= "cirrus,ep7209-mctrl-gpio",
+		.data		= &clps711x_mctrl_gpio,
+	},
+	{
+		.compatible	= "ti,keystone-dsp-gpio",
+		.data		= &keystone_dsp_gpio,
+	},
+	{
+		.compatible	= "rockchip,rk3328-grf-gpio",
+		.data		= &rockchip_rk3328_gpio_mute,
+	},
+	{ }
+};
+MODULE_DEVICE_TABLE(of, syscon_gpio_ids);
+
+static int syscon_gpio_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct syscon_gpio_priv *priv;
+	struct device_node *np = dev->of_node;
+	int ret;
+	bool use_parent_regmap = false;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->data = of_device_get_match_data(dev);
+
+	priv->syscon = syscon_regmap_lookup_by_phandle(np, "gpio,syscon-dev");
+	if (IS_ERR(priv->syscon) && np->parent) {
+		priv->syscon = syscon_node_to_regmap(np->parent);
+		use_parent_regmap = true;
+	}
+	if (IS_ERR(priv->syscon))
+		return PTR_ERR(priv->syscon);
+
+	if (!use_parent_regmap) {
+		ret = of_property_read_u32_index(np, "gpio,syscon-dev", 1,
+						 &priv->dreg_offset);
+		if (ret)
+			dev_err(dev, "can't read the data register offset!\n");
+
+		priv->dreg_offset <<= 3;
+
+		ret = of_property_read_u32_index(np, "gpio,syscon-dev", 2,
+						 &priv->dir_reg_offset);
+		if (ret)
+			dev_dbg(dev, "can't read the dir register offset!\n");
+
+		priv->dir_reg_offset <<= 3;
+	}
+
+	priv->chip.parent = dev;
+	priv->chip.owner = THIS_MODULE;
+	priv->chip.label = dev_name(dev);
+	priv->chip.base = -1;
+	priv->chip.ngpio = priv->data->bit_count;
+	priv->chip.get = syscon_gpio_get;
+	if (priv->data->flags & GPIO_SYSCON_FEAT_IN)
+		priv->chip.direction_input = syscon_gpio_dir_in;
+	if (priv->data->flags & GPIO_SYSCON_FEAT_OUT) {
+		priv->chip.set = priv->data->set ? : syscon_gpio_set;
+		priv->chip.direction_output = syscon_gpio_dir_out;
+	}
+
+	return devm_gpiochip_add_data(&pdev->dev, &priv->chip, priv);
+}
+
+static struct platform_driver syscon_gpio_driver = {
+	.driver	= {
+		.name		= "gpio-syscon",
+		.of_match_table	= syscon_gpio_ids,
+	},
+	.probe	= syscon_gpio_probe,
+};
+module_platform_driver(syscon_gpio_driver);
+
+MODULE_AUTHOR("Alexander Shiyan <shc_work@mail.ru>");
+MODULE_DESCRIPTION("SYSCON GPIO driver");
+MODULE_LICENSE("GPL");