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, 424 insertions, 0 deletions

diff --git a/drivers/clk/clk-fixed-factor.c b/drivers/clk/clk-fixed-factor.c
new file mode 100644
index 000000000..850e8b95f
--- /dev/null
+++ b/drivers/clk/clk-fixed-factor.c
@@ -0,0 +1,424 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2011 Sascha Hauer, Pengutronix <s.hauer@pengutronix.de>
+ */
+#include <linux/module.h>
+#include <linux/clk-provider.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+
+/*
+ * DOC: basic fixed multiplier and divider clock that cannot gate
+ *
+ * Traits of this clock:
+ * prepare - clk_prepare only ensures that parents are prepared
+ * enable - clk_enable only ensures that parents are enabled
+ * rate - rate is fixed.  clk->rate = parent->rate / div * mult
+ * parent - fixed parent.  No clk_set_parent support
+ */
+
+static unsigned long clk_factor_recalc_rate(struct clk_hw *hw,
+		unsigned long parent_rate)
+{
+	struct clk_fixed_factor *fix = to_clk_fixed_factor(hw);
+	unsigned long long int rate;
+
+	rate = (unsigned long long int)parent_rate * fix->mult;
+	do_div(rate, fix->div);
+	return (unsigned long)rate;
+}
+
+static int clk_factor_determine_rate(struct clk_hw *hw,
+				     struct clk_rate_request *req)
+{
+	struct clk_fixed_factor *fix = to_clk_fixed_factor(hw);
+
+	if (clk_hw_get_flags(hw) & CLK_SET_RATE_PARENT) {
+		unsigned long best_parent;
+
+		best_parent = (req->rate / fix->mult) * fix->div;
+		req->best_parent_rate = clk_hw_round_rate(clk_hw_get_parent(hw), best_parent);
+	}
+
+	req->rate = (req->best_parent_rate / fix->div) * fix->mult;
+
+	return 0;
+}
+
+static int clk_factor_set_rate(struct clk_hw *hw, unsigned long rate,
+				unsigned long parent_rate)
+{
+	/*
+	 * We must report success but we can do so unconditionally because
+	 * clk_factor_determine_rate returns values that ensure this call is a
+	 * nop.
+	 */
+
+	return 0;
+}
+
+static unsigned long clk_factor_recalc_accuracy(struct clk_hw *hw,
+						unsigned long parent_accuracy)
+{
+	struct clk_fixed_factor *fix = to_clk_fixed_factor(hw);
+
+	if (fix->flags & CLK_FIXED_FACTOR_FIXED_ACCURACY)
+		return fix->acc;
+
+	return parent_accuracy;
+}
+
+const struct clk_ops clk_fixed_factor_ops = {
+	.determine_rate = clk_factor_determine_rate,
+	.set_rate = clk_factor_set_rate,
+	.recalc_rate = clk_factor_recalc_rate,
+	.recalc_accuracy = clk_factor_recalc_accuracy,
+};
+EXPORT_SYMBOL_GPL(clk_fixed_factor_ops);
+
+static void devm_clk_hw_register_fixed_factor_release(struct device *dev, void *res)
+{
+	struct clk_fixed_factor *fix = res;
+
+	/*
+	 * We can not use clk_hw_unregister_fixed_factor, since it will kfree()
+	 * the hw, resulting in double free. Just unregister the hw and let
+	 * devres code kfree() it.
+	 */
+	clk_hw_unregister(&fix->hw);
+}
+
+static struct clk_hw *
+__clk_hw_register_fixed_factor(struct device *dev, struct device_node *np,
+		const char *name, const char *parent_name,
+		const struct clk_hw *parent_hw, const struct clk_parent_data *pdata,
+		unsigned long flags, unsigned int mult, unsigned int div,
+		unsigned long acc, unsigned int fixflags, bool devm)
+{
+	struct clk_fixed_factor *fix;
+	struct clk_init_data init = { };
+	struct clk_hw *hw;
+	int ret;
+
+	/* You can't use devm without a dev */
+	if (devm && !dev)
+		return ERR_PTR(-EINVAL);
+
+	if (devm)
+		fix = devres_alloc(devm_clk_hw_register_fixed_factor_release,
+				sizeof(*fix), GFP_KERNEL);
+	else
+		fix = kmalloc_obj(*fix);
+	if (!fix)
+		return ERR_PTR(-ENOMEM);
+
+	/* struct clk_fixed_factor assignments */
+	fix->mult = mult;
+	fix->div = div;
+	fix->hw.init = &init;
+	fix->acc = acc;
+	fix->flags = fixflags;
+
+	init.name = name;
+	init.ops = &clk_fixed_factor_ops;
+	init.flags = flags;
+	if (parent_name)
+		init.parent_names = &parent_name;
+	else if (parent_hw)
+		init.parent_hws = &parent_hw;
+	else
+		init.parent_data = pdata;
+	init.num_parents = 1;
+
+	hw = &fix->hw;
+	if (dev)
+		ret = clk_hw_register(dev, hw);
+	else
+		ret = of_clk_hw_register(np, hw);
+	if (ret) {
+		if (devm)
+			devres_free(fix);
+		else
+			kfree(fix);
+		hw = ERR_PTR(ret);
+	} else if (devm)
+		devres_add(dev, fix);
+
+	return hw;
+}
+
+/**
+ * devm_clk_hw_register_fixed_factor_index - Register a fixed factor clock with
+ * parent from DT index
+ * @dev: device that is registering this clock
+ * @name: name of this clock
+ * @index: index of phandle in @dev 'clocks' property
+ * @flags: fixed factor flags
+ * @mult: multiplier
+ * @div: divider
+ *
+ * Return: Pointer to fixed factor clk_hw structure that was registered or
+ * an error pointer.
+ */
+struct clk_hw *devm_clk_hw_register_fixed_factor_index(struct device *dev,
+		const char *name, unsigned int index, unsigned long flags,
+		unsigned int mult, unsigned int div)
+{
+	const struct clk_parent_data pdata = { .index = index };
+
+	return __clk_hw_register_fixed_factor(dev, NULL, name, NULL, NULL, &pdata,
+					      flags, mult, div, 0, 0, true);
+}
+EXPORT_SYMBOL_GPL(devm_clk_hw_register_fixed_factor_index);
+
+/**
+ * devm_clk_hw_register_fixed_factor_parent_hw - Register a fixed factor clock with
+ * pointer to parent clock
+ * @dev: device that is registering this clock
+ * @name: name of this clock
+ * @parent_hw: pointer to parent clk
+ * @flags: fixed factor flags
+ * @mult: multiplier
+ * @div: divider
+ *
+ * Return: Pointer to fixed factor clk_hw structure that was registered or
+ * an error pointer.
+ */
+struct clk_hw *devm_clk_hw_register_fixed_factor_parent_hw(struct device *dev,
+		const char *name, const struct clk_hw *parent_hw,
+		unsigned long flags, unsigned int mult, unsigned int div)
+{
+	const struct clk_parent_data pdata = { .index = -1 };
+
+	return __clk_hw_register_fixed_factor(dev, NULL, name, NULL, parent_hw,
+					      &pdata, flags, mult, div, 0, 0, true);
+}
+EXPORT_SYMBOL_GPL(devm_clk_hw_register_fixed_factor_parent_hw);
+
+struct clk_hw *clk_hw_register_fixed_factor_parent_hw(struct device *dev,
+		const char *name, const struct clk_hw *parent_hw,
+		unsigned long flags, unsigned int mult, unsigned int div)
+{
+	const struct clk_parent_data pdata = { .index = -1 };
+
+	return __clk_hw_register_fixed_factor(dev, NULL, name, NULL, parent_hw,
+					      &pdata, flags, mult, div, 0, 0, false);
+}
+EXPORT_SYMBOL_GPL(clk_hw_register_fixed_factor_parent_hw);
+
+struct clk_hw *clk_hw_register_fixed_factor(struct device *dev,
+		const char *name, const char *parent_name, unsigned long flags,
+		unsigned int mult, unsigned int div)
+{
+	const struct clk_parent_data pdata = { .index = -1 };
+
+	return __clk_hw_register_fixed_factor(dev, NULL, name, parent_name, NULL,
+					      &pdata, flags, mult, div, 0, 0, false);
+}
+EXPORT_SYMBOL_GPL(clk_hw_register_fixed_factor);
+
+struct clk_hw *clk_hw_register_fixed_factor_fwname(struct device *dev,
+		struct device_node *np, const char *name, const char *fw_name,
+		unsigned long flags, unsigned int mult, unsigned int div)
+{
+	const struct clk_parent_data pdata = { .index = -1, .fw_name = fw_name };
+
+	return __clk_hw_register_fixed_factor(dev, np, name, NULL, NULL,
+			&pdata, flags, mult, div, 0, 0, false);
+}
+EXPORT_SYMBOL_GPL(clk_hw_register_fixed_factor_fwname);
+
+struct clk_hw *clk_hw_register_fixed_factor_with_accuracy_fwname(struct device *dev,
+		struct device_node *np, const char *name, const char *fw_name,
+		unsigned long flags, unsigned int mult, unsigned int div,
+		unsigned long acc)
+{
+	const struct clk_parent_data pdata = { .index = -1, .fw_name = fw_name };
+
+	return __clk_hw_register_fixed_factor(dev, np, name, NULL, NULL,
+			&pdata, flags, mult, div, acc,
+			CLK_FIXED_FACTOR_FIXED_ACCURACY, false);
+}
+EXPORT_SYMBOL_GPL(clk_hw_register_fixed_factor_with_accuracy_fwname);
+
+struct clk_hw *clk_hw_register_fixed_factor_index(struct device *dev,
+		const char *name, unsigned int index, unsigned long flags,
+		unsigned int mult, unsigned int div)
+{
+	const struct clk_parent_data pdata = { .index = index };
+
+	return __clk_hw_register_fixed_factor(dev, NULL, name, NULL, NULL, &pdata,
+					      flags, mult, div, 0, 0, false);
+}
+EXPORT_SYMBOL_GPL(clk_hw_register_fixed_factor_index);
+
+struct clk *clk_register_fixed_factor(struct device *dev, const char *name,
+		const char *parent_name, unsigned long flags,
+		unsigned int mult, unsigned int div)
+{
+	struct clk_hw *hw;
+
+	hw = clk_hw_register_fixed_factor(dev, name, parent_name, flags, mult,
+					  div);
+	if (IS_ERR(hw))
+		return ERR_CAST(hw);
+	return hw->clk;
+}
+EXPORT_SYMBOL_GPL(clk_register_fixed_factor);
+
+void clk_unregister_fixed_factor(struct clk *clk)
+{
+	struct clk_hw *hw;
+
+	hw = __clk_get_hw(clk);
+	if (!hw)
+		return;
+
+	clk_unregister(clk);
+	kfree(to_clk_fixed_factor(hw));
+}
+EXPORT_SYMBOL_GPL(clk_unregister_fixed_factor);
+
+void clk_hw_unregister_fixed_factor(struct clk_hw *hw)
+{
+	struct clk_fixed_factor *fix;
+
+	fix = to_clk_fixed_factor(hw);
+
+	clk_hw_unregister(hw);
+	kfree(fix);
+}
+EXPORT_SYMBOL_GPL(clk_hw_unregister_fixed_factor);
+
+struct clk_hw *devm_clk_hw_register_fixed_factor(struct device *dev,
+		const char *name, const char *parent_name, unsigned long flags,
+		unsigned int mult, unsigned int div)
+{
+	const struct clk_parent_data pdata = { .index = -1 };
+
+	return __clk_hw_register_fixed_factor(dev, NULL, name, parent_name, NULL,
+			&pdata, flags, mult, div, 0, 0, true);
+}
+EXPORT_SYMBOL_GPL(devm_clk_hw_register_fixed_factor);
+
+struct clk_hw *devm_clk_hw_register_fixed_factor_fwname(struct device *dev,
+		struct device_node *np, const char *name, const char *fw_name,
+		unsigned long flags, unsigned int mult, unsigned int div)
+{
+	const struct clk_parent_data pdata = { .index = -1, .fw_name = fw_name };
+
+	return __clk_hw_register_fixed_factor(dev, np, name, NULL, NULL,
+			&pdata, flags, mult, div, 0, 0, true);
+}
+EXPORT_SYMBOL_GPL(devm_clk_hw_register_fixed_factor_fwname);
+
+struct clk_hw *devm_clk_hw_register_fixed_factor_with_accuracy_fwname(struct device *dev,
+		struct device_node *np, const char *name, const char *fw_name,
+		unsigned long flags, unsigned int mult, unsigned int div,
+		unsigned long acc)
+{
+	const struct clk_parent_data pdata = { .index = -1, .fw_name = fw_name };
+
+	return __clk_hw_register_fixed_factor(dev, np, name, NULL, NULL,
+			&pdata, flags, mult, div, acc,
+			CLK_FIXED_FACTOR_FIXED_ACCURACY, true);
+}
+EXPORT_SYMBOL_GPL(devm_clk_hw_register_fixed_factor_with_accuracy_fwname);
+
+#ifdef CONFIG_OF
+static struct clk_hw *_of_fixed_factor_clk_setup(struct device_node *node)
+{
+	struct clk_hw *hw;
+	const char *clk_name = node->name;
+	const struct clk_parent_data pdata = { .index = 0 };
+	u32 div, mult;
+	int ret;
+
+	if (of_property_read_u32(node, "clock-div", &div)) {
+		pr_err("%s Fixed factor clock <%pOFn> must have a clock-div property\n",
+			__func__, node);
+		return ERR_PTR(-EIO);
+	}
+
+	if (of_property_read_u32(node, "clock-mult", &mult)) {
+		pr_err("%s Fixed factor clock <%pOFn> must have a clock-mult property\n",
+			__func__, node);
+		return ERR_PTR(-EIO);
+	}
+
+	of_property_read_string(node, "clock-output-names", &clk_name);
+
+	hw = __clk_hw_register_fixed_factor(NULL, node, clk_name, NULL, NULL,
+					    &pdata, 0, mult, div, 0, 0, false);
+	if (IS_ERR(hw)) {
+		/*
+		 * Clear OF_POPULATED flag so that clock registration can be
+		 * attempted again from probe function.
+		 */
+		of_node_clear_flag(node, OF_POPULATED);
+		return ERR_CAST(hw);
+	}
+
+	ret = of_clk_add_hw_provider(node, of_clk_hw_simple_get, hw);
+	if (ret) {
+		clk_hw_unregister_fixed_factor(hw);
+		return ERR_PTR(ret);
+	}
+
+	return hw;
+}
+
+/**
+ * of_fixed_factor_clk_setup() - Setup function for simple fixed factor clock
+ * @node:	device node for the clock
+ */
+void __init of_fixed_factor_clk_setup(struct device_node *node)
+{
+	_of_fixed_factor_clk_setup(node);
+}
+CLK_OF_DECLARE(fixed_factor_clk, "fixed-factor-clock",
+		of_fixed_factor_clk_setup);
+
+static void of_fixed_factor_clk_remove(struct platform_device *pdev)
+{
+	struct clk_hw *clk = platform_get_drvdata(pdev);
+
+	of_clk_del_provider(pdev->dev.of_node);
+	clk_hw_unregister_fixed_factor(clk);
+}
+
+static int of_fixed_factor_clk_probe(struct platform_device *pdev)
+{
+	struct clk_hw *clk;
+
+	/*
+	 * This function is not executed when of_fixed_factor_clk_setup
+	 * succeeded.
+	 */
+	clk = _of_fixed_factor_clk_setup(pdev->dev.of_node);
+	if (IS_ERR(clk))
+		return PTR_ERR(clk);
+
+	platform_set_drvdata(pdev, clk);
+
+	return 0;
+}
+
+static const struct of_device_id of_fixed_factor_clk_ids[] = {
+	{ .compatible = "fixed-factor-clock" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, of_fixed_factor_clk_ids);
+
+static struct platform_driver of_fixed_factor_clk_driver = {
+	.driver = {
+		.name = "of_fixed_factor_clk",
+		.of_match_table = of_fixed_factor_clk_ids,
+	},
+	.probe = of_fixed_factor_clk_probe,
+	.remove = of_fixed_factor_clk_remove,
+};
+builtin_platform_driver(of_fixed_factor_clk_driver);
+#endif