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, 232 insertions, 0 deletions

diff --git a/drivers/reset/reset-ma35d1.c b/drivers/reset/reset-ma35d1.c
new file mode 100644
index 000000000..4ee901f00
--- /dev/null
+++ b/drivers/reset/reset-ma35d1.c
@@ -0,0 +1,232 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023 Nuvoton Technology Corp.
+ * Author: Chi-Fang Li <cfli0@nuvoton.com>
+ */
+
+#include <linux/bits.h>
+#include <linux/container_of.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/reboot.h>
+#include <linux/reset-controller.h>
+#include <linux/spinlock.h>
+#include <dt-bindings/reset/nuvoton,ma35d1-reset.h>
+
+struct ma35d1_reset_data {
+	struct reset_controller_dev rcdev;
+	void __iomem *base;
+	/* protect registers against concurrent read-modify-write */
+	spinlock_t lock;
+};
+
+static const struct {
+	u32 reg_ofs;
+	u32 bit;
+} ma35d1_reset_map[] = {
+	[MA35D1_RESET_CHIP] =    {0x20, 0},
+	[MA35D1_RESET_CA35CR0] = {0x20, 1},
+	[MA35D1_RESET_CA35CR1] = {0x20, 2},
+	[MA35D1_RESET_CM4] =     {0x20, 3},
+	[MA35D1_RESET_PDMA0] =   {0x20, 4},
+	[MA35D1_RESET_PDMA1] =   {0x20, 5},
+	[MA35D1_RESET_PDMA2] =   {0x20, 6},
+	[MA35D1_RESET_PDMA3] =   {0x20, 7},
+	[MA35D1_RESET_DISP] =    {0x20, 9},
+	[MA35D1_RESET_VCAP0] =   {0x20, 10},
+	[MA35D1_RESET_VCAP1] =   {0x20, 11},
+	[MA35D1_RESET_GFX] =     {0x20, 12},
+	[MA35D1_RESET_VDEC] =    {0x20, 13},
+	[MA35D1_RESET_WHC0] =    {0x20, 14},
+	[MA35D1_RESET_WHC1] =    {0x20, 15},
+	[MA35D1_RESET_GMAC0] =   {0x20, 16},
+	[MA35D1_RESET_GMAC1] =   {0x20, 17},
+	[MA35D1_RESET_HWSEM] =   {0x20, 18},
+	[MA35D1_RESET_EBI] =     {0x20, 19},
+	[MA35D1_RESET_HSUSBH0] = {0x20, 20},
+	[MA35D1_RESET_HSUSBH1] = {0x20, 21},
+	[MA35D1_RESET_HSUSBD] =  {0x20, 22},
+	[MA35D1_RESET_USBHL] =   {0x20, 23},
+	[MA35D1_RESET_SDH0] =    {0x20, 24},
+	[MA35D1_RESET_SDH1] =    {0x20, 25},
+	[MA35D1_RESET_NAND] =    {0x20, 26},
+	[MA35D1_RESET_GPIO] =    {0x20, 27},
+	[MA35D1_RESET_MCTLP] =   {0x20, 28},
+	[MA35D1_RESET_MCTLC] =   {0x20, 29},
+	[MA35D1_RESET_DDRPUB] =  {0x20, 30},
+	[MA35D1_RESET_TMR0] =    {0x24, 2},
+	[MA35D1_RESET_TMR1] =    {0x24, 3},
+	[MA35D1_RESET_TMR2] =    {0x24, 4},
+	[MA35D1_RESET_TMR3] =    {0x24, 5},
+	[MA35D1_RESET_I2C0] =    {0x24, 8},
+	[MA35D1_RESET_I2C1] =    {0x24, 9},
+	[MA35D1_RESET_I2C2] =    {0x24, 10},
+	[MA35D1_RESET_I2C3] =    {0x24, 11},
+	[MA35D1_RESET_QSPI0] =   {0x24, 12},
+	[MA35D1_RESET_SPI0] =    {0x24, 13},
+	[MA35D1_RESET_SPI1] =    {0x24, 14},
+	[MA35D1_RESET_SPI2] =    {0x24, 15},
+	[MA35D1_RESET_UART0] =   {0x24, 16},
+	[MA35D1_RESET_UART1] =   {0x24, 17},
+	[MA35D1_RESET_UART2] =   {0x24, 18},
+	[MA35D1_RESET_UART3] =   {0x24, 19},
+	[MA35D1_RESET_UART4] =   {0x24, 20},
+	[MA35D1_RESET_UART5] =   {0x24, 21},
+	[MA35D1_RESET_UART6] =   {0x24, 22},
+	[MA35D1_RESET_UART7] =   {0x24, 23},
+	[MA35D1_RESET_CANFD0] =  {0x24, 24},
+	[MA35D1_RESET_CANFD1] =  {0x24, 25},
+	[MA35D1_RESET_EADC0] =   {0x24, 28},
+	[MA35D1_RESET_I2S0] =    {0x24, 29},
+	[MA35D1_RESET_SC0] =     {0x28, 0},
+	[MA35D1_RESET_SC1] =     {0x28, 1},
+	[MA35D1_RESET_QSPI1] =   {0x28, 4},
+	[MA35D1_RESET_SPI3] =    {0x28, 6},
+	[MA35D1_RESET_EPWM0] =   {0x28, 16},
+	[MA35D1_RESET_EPWM1] =   {0x28, 17},
+	[MA35D1_RESET_QEI0] =    {0x28, 22},
+	[MA35D1_RESET_QEI1] =    {0x28, 23},
+	[MA35D1_RESET_ECAP0] =   {0x28, 26},
+	[MA35D1_RESET_ECAP1] =   {0x28, 27},
+	[MA35D1_RESET_CANFD2] =  {0x28, 28},
+	[MA35D1_RESET_ADC0] =    {0x28, 31},
+	[MA35D1_RESET_TMR4] =    {0x2C, 0},
+	[MA35D1_RESET_TMR5] =    {0x2C, 1},
+	[MA35D1_RESET_TMR6] =    {0x2C, 2},
+	[MA35D1_RESET_TMR7] =    {0x2C, 3},
+	[MA35D1_RESET_TMR8] =    {0x2C, 4},
+	[MA35D1_RESET_TMR9] =    {0x2C, 5},
+	[MA35D1_RESET_TMR10] =   {0x2C, 6},
+	[MA35D1_RESET_TMR11] =   {0x2C, 7},
+	[MA35D1_RESET_UART8] =   {0x2C, 8},
+	[MA35D1_RESET_UART9] =   {0x2C, 9},
+	[MA35D1_RESET_UART10] =  {0x2C, 10},
+	[MA35D1_RESET_UART11] =  {0x2C, 11},
+	[MA35D1_RESET_UART12] =  {0x2C, 12},
+	[MA35D1_RESET_UART13] =  {0x2C, 13},
+	[MA35D1_RESET_UART14] =  {0x2C, 14},
+	[MA35D1_RESET_UART15] =  {0x2C, 15},
+	[MA35D1_RESET_UART16] =  {0x2C, 16},
+	[MA35D1_RESET_I2S1] =    {0x2C, 17},
+	[MA35D1_RESET_I2C4] =    {0x2C, 18},
+	[MA35D1_RESET_I2C5] =    {0x2C, 19},
+	[MA35D1_RESET_EPWM2] =   {0x2C, 20},
+	[MA35D1_RESET_ECAP2] =   {0x2C, 21},
+	[MA35D1_RESET_QEI2] =    {0x2C, 22},
+	[MA35D1_RESET_CANFD3] =  {0x2C, 23},
+	[MA35D1_RESET_KPI] =     {0x2C, 24},
+	[MA35D1_RESET_GIC] =     {0x2C, 28},
+	[MA35D1_RESET_SSMCC] =   {0x2C, 30},
+	[MA35D1_RESET_SSPCC] =   {0x2C, 31}
+};
+
+static int ma35d1_restart_handler(struct sys_off_data *sys_off_data)
+{
+	struct ma35d1_reset_data *data = sys_off_data->cb_data;
+	u32 id = MA35D1_RESET_CHIP;
+
+	writel_relaxed(BIT(ma35d1_reset_map[id].bit),
+		       data->base + ma35d1_reset_map[id].reg_ofs);
+	return 0;
+}
+
+static int ma35d1_reset_update(struct reset_controller_dev *rcdev, unsigned long id, bool assert)
+{
+	struct ma35d1_reset_data *data = container_of(rcdev, struct ma35d1_reset_data, rcdev);
+	unsigned long flags;
+	u32 reg;
+
+	if (WARN_ON_ONCE(id >= ARRAY_SIZE(ma35d1_reset_map)))
+		return -EINVAL;
+
+	spin_lock_irqsave(&data->lock, flags);
+	reg = readl_relaxed(data->base + ma35d1_reset_map[id].reg_ofs);
+	if (assert)
+		reg |= BIT(ma35d1_reset_map[id].bit);
+	else
+		reg &= ~(BIT(ma35d1_reset_map[id].bit));
+	writel_relaxed(reg, data->base + ma35d1_reset_map[id].reg_ofs);
+	spin_unlock_irqrestore(&data->lock, flags);
+
+	return 0;
+}
+
+static int ma35d1_reset_assert(struct reset_controller_dev *rcdev, unsigned long id)
+{
+	return ma35d1_reset_update(rcdev, id, true);
+}
+
+static int ma35d1_reset_deassert(struct reset_controller_dev *rcdev, unsigned long id)
+{
+	return ma35d1_reset_update(rcdev, id, false);
+}
+
+static int ma35d1_reset_status(struct reset_controller_dev *rcdev, unsigned long id)
+{
+	struct ma35d1_reset_data *data = container_of(rcdev, struct ma35d1_reset_data, rcdev);
+	u32 reg;
+
+	if (WARN_ON_ONCE(id >= ARRAY_SIZE(ma35d1_reset_map)))
+		return -EINVAL;
+
+	reg = readl_relaxed(data->base + ma35d1_reset_map[id].reg_ofs);
+	return !!(reg & BIT(ma35d1_reset_map[id].bit));
+}
+
+static const struct reset_control_ops ma35d1_reset_ops = {
+	.assert = ma35d1_reset_assert,
+	.deassert = ma35d1_reset_deassert,
+	.status = ma35d1_reset_status,
+};
+
+static const struct of_device_id ma35d1_reset_dt_ids[] = {
+	{ .compatible = "nuvoton,ma35d1-reset" },
+	{ },
+};
+
+static int ma35d1_reset_probe(struct platform_device *pdev)
+{
+	struct ma35d1_reset_data *reset_data;
+	struct device *dev = &pdev->dev;
+	int err;
+
+	if (!pdev->dev.of_node) {
+		dev_err(&pdev->dev, "Device tree node not found\n");
+		return -EINVAL;
+	}
+
+	reset_data = devm_kzalloc(dev, sizeof(*reset_data), GFP_KERNEL);
+	if (!reset_data)
+		return -ENOMEM;
+
+	reset_data->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(reset_data->base))
+		return PTR_ERR(reset_data->base);
+
+	reset_data->rcdev.owner = THIS_MODULE;
+	reset_data->rcdev.nr_resets = MA35D1_RESET_COUNT;
+	reset_data->rcdev.ops = &ma35d1_reset_ops;
+	reset_data->rcdev.of_node = dev->of_node;
+	spin_lock_init(&reset_data->lock);
+
+	err = devm_register_sys_off_handler(dev, SYS_OFF_MODE_RESTART, 192,
+					    ma35d1_restart_handler, reset_data);
+	if (err)
+		dev_warn(&pdev->dev, "failed to register restart handler\n");
+
+	return devm_reset_controller_register(dev, &reset_data->rcdev);
+}
+
+static struct platform_driver ma35d1_reset_driver = {
+	.probe = ma35d1_reset_probe,
+	.driver = {
+		.name = "ma35d1-reset",
+		.of_match_table	= ma35d1_reset_dt_ids,
+	},
+};
+
+builtin_platform_driver(ma35d1_reset_driver);