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, 174 insertions, 0 deletions

diff --git a/drivers/clk/mediatek/reset.c b/drivers/clk/mediatek/reset.c
new file mode 100644
index 000000000..2e3303975
--- /dev/null
+++ b/drivers/clk/mediatek/reset.c
@@ -0,0 +1,174 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2014 MediaTek Inc.
+ */
+
+#include <linux/mfd/syscon.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+
+#include "reset.h"
+
+static inline struct mtk_clk_rst_data *to_mtk_clk_rst_data(struct reset_controller_dev *rcdev)
+{
+	return container_of(rcdev, struct mtk_clk_rst_data, rcdev);
+}
+
+static int mtk_reset_update(struct reset_controller_dev *rcdev,
+			    unsigned long id, bool deassert)
+{
+	struct mtk_clk_rst_data *data = to_mtk_clk_rst_data(rcdev);
+	unsigned int val = deassert ? 0 : ~0;
+
+	return regmap_update_bits(data->regmap,
+				  data->desc->rst_bank_ofs[id / RST_NR_PER_BANK],
+				  BIT(id % RST_NR_PER_BANK), val);
+}
+
+static int mtk_reset_assert(struct reset_controller_dev *rcdev,
+			    unsigned long id)
+{
+	return mtk_reset_update(rcdev, id, false);
+}
+
+static int mtk_reset_deassert(struct reset_controller_dev *rcdev,
+			      unsigned long id)
+{
+	return mtk_reset_update(rcdev, id, true);
+}
+
+static int mtk_reset(struct reset_controller_dev *rcdev, unsigned long id)
+{
+	int ret;
+
+	ret = mtk_reset_assert(rcdev, id);
+	if (ret)
+		return ret;
+
+	return mtk_reset_deassert(rcdev, id);
+}
+
+static int mtk_reset_update_set_clr(struct reset_controller_dev *rcdev,
+				    unsigned long id, bool deassert)
+{
+	struct mtk_clk_rst_data *data = to_mtk_clk_rst_data(rcdev);
+	unsigned int deassert_ofs = deassert ? 0x4 : 0;
+
+	return regmap_write(data->regmap,
+			    data->desc->rst_bank_ofs[id / RST_NR_PER_BANK] +
+			    deassert_ofs,
+			    BIT(id % RST_NR_PER_BANK));
+}
+
+static int mtk_reset_assert_set_clr(struct reset_controller_dev *rcdev,
+				    unsigned long id)
+{
+	return mtk_reset_update_set_clr(rcdev, id, false);
+}
+
+static int mtk_reset_deassert_set_clr(struct reset_controller_dev *rcdev,
+				      unsigned long id)
+{
+	return mtk_reset_update_set_clr(rcdev, id, true);
+}
+
+static int mtk_reset_set_clr(struct reset_controller_dev *rcdev,
+			     unsigned long id)
+{
+	int ret;
+
+	ret = mtk_reset_assert_set_clr(rcdev, id);
+	if (ret)
+		return ret;
+	return mtk_reset_deassert_set_clr(rcdev, id);
+}
+
+static const struct reset_control_ops mtk_reset_ops = {
+	.assert = mtk_reset_assert,
+	.deassert = mtk_reset_deassert,
+	.reset = mtk_reset,
+};
+
+static const struct reset_control_ops mtk_reset_ops_set_clr = {
+	.assert = mtk_reset_assert_set_clr,
+	.deassert = mtk_reset_deassert_set_clr,
+	.reset = mtk_reset_set_clr,
+};
+
+static int reset_xlate(struct reset_controller_dev *rcdev,
+		       const struct of_phandle_args *reset_spec)
+{
+	struct mtk_clk_rst_data *data = to_mtk_clk_rst_data(rcdev);
+
+	if (reset_spec->args[0] >= rcdev->nr_resets ||
+	    reset_spec->args[0] >= data->desc->rst_idx_map_nr)
+		return -EINVAL;
+
+	return data->desc->rst_idx_map[reset_spec->args[0]];
+}
+
+int mtk_register_reset_controller_with_dev(struct device *dev,
+					   const struct mtk_clk_rst_desc *desc)
+{
+	struct device_node *np = dev->of_node;
+	struct regmap *regmap;
+	const struct reset_control_ops *rcops = NULL;
+	struct mtk_clk_rst_data *data;
+	int ret;
+
+	if (!desc) {
+		dev_err(dev, "mtk clock reset desc is NULL\n");
+		return -EINVAL;
+	}
+
+	switch (desc->version) {
+	case MTK_RST_SIMPLE:
+		rcops = &mtk_reset_ops;
+		break;
+	case MTK_RST_SET_CLR:
+		rcops = &mtk_reset_ops_set_clr;
+		break;
+	default:
+		dev_err(dev, "Unknown reset version %d\n", desc->version);
+		return -EINVAL;
+	}
+
+	regmap = device_node_to_regmap(np);
+	if (IS_ERR(regmap)) {
+		dev_err(dev, "Cannot find regmap %pe\n", regmap);
+		return PTR_ERR(regmap);
+	}
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->desc = desc;
+	data->regmap = regmap;
+	data->rcdev.owner = THIS_MODULE;
+	data->rcdev.ops = rcops;
+	data->rcdev.of_node = np;
+	data->rcdev.dev = dev;
+
+	if (data->desc->rst_idx_map_nr > 0) {
+		data->rcdev.of_reset_n_cells = 1;
+		data->rcdev.nr_resets = desc->rst_idx_map_nr;
+		data->rcdev.of_xlate = reset_xlate;
+	} else {
+		data->rcdev.nr_resets = desc->rst_bank_nr * RST_NR_PER_BANK;
+	}
+
+	ret = devm_reset_controller_register(dev, &data->rcdev);
+	if (ret) {
+		dev_err(dev, "could not register reset controller: %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(mtk_register_reset_controller_with_dev);
+
+MODULE_LICENSE("GPL");