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, 206 insertions, 0 deletions

diff --git a/drivers/reset/reset-sunplus.c b/drivers/reset/reset-sunplus.c
new file mode 100644
index 000000000..c136a1f07
--- /dev/null
+++ b/drivers/reset/reset-sunplus.c
@@ -0,0 +1,206 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+/*
+ * SP7021 reset driver
+ *
+ * Copyright (C) Sunplus Technology Co., Ltd.
+ *       All rights reserved.
+ */
+
+#include <linux/io.h>
+#include <linux/init.h>
+#include <linux/platform_device.h>
+#include <linux/reset-controller.h>
+#include <linux/reboot.h>
+
+/* HIWORD_MASK_REG BITS */
+#define BITS_PER_HWM_REG	16
+
+/* resets HW info: reg_index_shift */
+static const u32 sp_resets[] = {
+/* SP7021: mo_reset0 ~ mo_reset9 */
+	0x00,
+	0x02,
+	0x03,
+	0x04,
+	0x05,
+	0x06,
+	0x07,
+	0x08,
+	0x09,
+	0x0a,
+	0x0b,
+	0x0d,
+	0x0e,
+	0x0f,
+	0x10,
+	0x12,
+	0x14,
+	0x15,
+	0x16,
+	0x17,
+	0x18,
+	0x19,
+	0x1a,
+	0x1b,
+	0x1c,
+	0x1d,
+	0x1e,
+	0x1f,
+	0x20,
+	0x21,
+	0x22,
+	0x23,
+	0x24,
+	0x25,
+	0x26,
+	0x2a,
+	0x2b,
+	0x2d,
+	0x2e,
+	0x30,
+	0x31,
+	0x32,
+	0x33,
+	0x3d,
+	0x3e,
+	0x3f,
+	0x42,
+	0x44,
+	0x4b,
+	0x4c,
+	0x4d,
+	0x4e,
+	0x4f,
+	0x50,
+	0x55,
+	0x60,
+	0x61,
+	0x6a,
+	0x6f,
+	0x70,
+	0x73,
+	0x74,
+	0x86,
+	0x8a,
+	0x8b,
+	0x8d,
+	0x8e,
+	0x8f,
+	0x90,
+	0x92,
+	0x93,
+	0x94,
+	0x95,
+	0x96,
+	0x97,
+	0x98,
+	0x99,
+};
+
+struct sp_reset {
+	struct reset_controller_dev rcdev;
+	void __iomem *base;
+};
+
+static inline struct sp_reset *to_sp_reset(struct reset_controller_dev *rcdev)
+{
+	return container_of(rcdev, struct sp_reset, rcdev);
+}
+
+static int sp_reset_update(struct reset_controller_dev *rcdev,
+			   unsigned long id, bool assert)
+{
+	struct sp_reset *reset = to_sp_reset(rcdev);
+	int index = sp_resets[id] / BITS_PER_HWM_REG;
+	int shift = sp_resets[id] % BITS_PER_HWM_REG;
+	u32 val;
+
+	val = (1 << (16 + shift)) | (assert << shift);
+	writel(val, reset->base + (index * 4));
+
+	return 0;
+}
+
+static int sp_reset_assert(struct reset_controller_dev *rcdev,
+			   unsigned long id)
+{
+	return sp_reset_update(rcdev, id, true);
+}
+
+static int sp_reset_deassert(struct reset_controller_dev *rcdev,
+			     unsigned long id)
+{
+	return sp_reset_update(rcdev, id, false);
+}
+
+static int sp_reset_status(struct reset_controller_dev *rcdev,
+			   unsigned long id)
+{
+	struct sp_reset *reset = to_sp_reset(rcdev);
+	int index = sp_resets[id] / BITS_PER_HWM_REG;
+	int shift = sp_resets[id] % BITS_PER_HWM_REG;
+	u32 reg;
+
+	reg = readl(reset->base + (index * 4));
+
+	return !!(reg & BIT(shift));
+}
+
+static const struct reset_control_ops sp_reset_ops = {
+	.assert   = sp_reset_assert,
+	.deassert = sp_reset_deassert,
+	.status   = sp_reset_status,
+};
+
+static int sp_restart(struct sys_off_data *data)
+{
+	struct sp_reset *reset = data->cb_data;
+
+	sp_reset_assert(&reset->rcdev, 0);
+	sp_reset_deassert(&reset->rcdev, 0);
+
+	return NOTIFY_DONE;
+}
+
+static int sp_reset_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct sp_reset *reset;
+	struct resource *res;
+	int ret;
+
+	reset = devm_kzalloc(dev, sizeof(*reset), GFP_KERNEL);
+	if (!reset)
+		return -ENOMEM;
+
+	reset->base = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
+	if (IS_ERR(reset->base))
+		return PTR_ERR(reset->base);
+
+	reset->rcdev.ops = &sp_reset_ops;
+	reset->rcdev.owner = THIS_MODULE;
+	reset->rcdev.of_node = dev->of_node;
+	reset->rcdev.nr_resets = resource_size(res) / 4 * BITS_PER_HWM_REG;
+
+	ret = devm_reset_controller_register(dev, &reset->rcdev);
+	if (ret)
+		return ret;
+
+	return devm_register_sys_off_handler(&pdev->dev, SYS_OFF_MODE_RESTART,
+					     192, sp_restart, reset);
+}
+
+static const struct of_device_id sp_reset_dt_ids[] = {
+	{.compatible = "sunplus,sp7021-reset",},
+	{ /* sentinel */ },
+};
+
+static struct platform_driver sp_reset_driver = {
+	.probe = sp_reset_probe,
+	.driver = {
+		.name			= "sunplus-reset",
+		.of_match_table		= sp_reset_dt_ids,
+		.suppress_bind_attrs	= true,
+	},
+};
+builtin_platform_driver(sp_reset_driver);