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, 418 insertions, 0 deletions

diff --git a/drivers/clk/clkdev.c b/drivers/clk/clkdev.c
new file mode 100644
index 000000000..abaa0f9e0
--- /dev/null
+++ b/drivers/clk/clkdev.c
@@ -0,0 +1,418 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * drivers/clk/clkdev.c
+ *
+ *  Copyright (C) 2008 Russell King.
+ *
+ * Helper for the clk API to assist looking up a struct clk.
+ */
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/device.h>
+#include <linux/list.h>
+#include <linux/errno.h>
+#include <linux/err.h>
+#include <linux/string.h>
+#include <linux/mutex.h>
+#include <linux/clk.h>
+#include <linux/clkdev.h>
+#include <linux/clk-provider.h>
+#include <linux/of.h>
+
+#include "clk.h"
+
+static LIST_HEAD(clocks);
+static DEFINE_MUTEX(clocks_mutex);
+
+/*
+ * Find the correct struct clk for the device and connection ID.
+ * We do slightly fuzzy matching here:
+ *  An entry with a NULL ID is assumed to be a wildcard.
+ *  If an entry has a device ID, it must match
+ *  If an entry has a connection ID, it must match
+ * Then we take the most specific entry - with the following
+ * order of precedence: dev+con > dev only > con only.
+ */
+static struct clk_lookup *clk_find(const char *dev_id, const char *con_id)
+{
+	struct clk_lookup *p, *cl = NULL;
+	int match, best_found = 0, best_possible = 0;
+
+	if (dev_id)
+		best_possible += 2;
+	if (con_id)
+		best_possible += 1;
+
+	lockdep_assert_held(&clocks_mutex);
+
+	list_for_each_entry(p, &clocks, node) {
+		match = 0;
+		if (p->dev_id) {
+			if (!dev_id || strcmp(p->dev_id, dev_id))
+				continue;
+			match += 2;
+		}
+		if (p->con_id) {
+			if (!con_id || strcmp(p->con_id, con_id))
+				continue;
+			match += 1;
+		}
+
+		if (match > best_found) {
+			cl = p;
+			if (match != best_possible)
+				best_found = match;
+			else
+				break;
+		}
+	}
+	return cl;
+}
+
+struct clk_hw *clk_find_hw(const char *dev_id, const char *con_id)
+{
+	struct clk_lookup *cl;
+	struct clk_hw *hw = ERR_PTR(-ENOENT);
+
+	mutex_lock(&clocks_mutex);
+	cl = clk_find(dev_id, con_id);
+	if (cl)
+		hw = cl->clk_hw;
+	mutex_unlock(&clocks_mutex);
+
+	return hw;
+}
+
+static struct clk *__clk_get_sys(struct device *dev, const char *dev_id,
+				 const char *con_id)
+{
+	struct clk_hw *hw = clk_find_hw(dev_id, con_id);
+
+	return clk_hw_create_clk(dev, hw, dev_id, con_id);
+}
+
+struct clk *clk_get_sys(const char *dev_id, const char *con_id)
+{
+	return __clk_get_sys(NULL, dev_id, con_id);
+}
+EXPORT_SYMBOL(clk_get_sys);
+
+struct clk *clk_get(struct device *dev, const char *con_id)
+{
+	const char *dev_id = dev ? dev_name(dev) : NULL;
+	struct clk_hw *hw;
+
+	if (dev && dev->of_node) {
+		hw = of_clk_get_hw(dev->of_node, 0, con_id);
+		if (!IS_ERR(hw) || PTR_ERR(hw) == -EPROBE_DEFER)
+			return clk_hw_create_clk(dev, hw, dev_id, con_id);
+	}
+
+	return __clk_get_sys(dev, dev_id, con_id);
+}
+EXPORT_SYMBOL(clk_get);
+
+void clk_put(struct clk *clk)
+{
+	__clk_put(clk);
+}
+EXPORT_SYMBOL(clk_put);
+
+static void __clkdev_add(struct clk_lookup *cl)
+{
+	mutex_lock(&clocks_mutex);
+	list_add_tail(&cl->node, &clocks);
+	mutex_unlock(&clocks_mutex);
+}
+
+void clkdev_add(struct clk_lookup *cl)
+{
+	if (!cl->clk_hw)
+		cl->clk_hw = __clk_get_hw(cl->clk);
+	__clkdev_add(cl);
+}
+EXPORT_SYMBOL(clkdev_add);
+
+void clkdev_add_table(struct clk_lookup *cl, size_t num)
+{
+	mutex_lock(&clocks_mutex);
+	while (num--) {
+		cl->clk_hw = __clk_get_hw(cl->clk);
+		list_add_tail(&cl->node, &clocks);
+		cl++;
+	}
+	mutex_unlock(&clocks_mutex);
+}
+
+#define MAX_DEV_ID	24
+#define MAX_CON_ID	16
+
+struct clk_lookup_alloc {
+	struct clk_lookup cl;
+	char	dev_id[MAX_DEV_ID];
+	char	con_id[MAX_CON_ID];
+};
+
+static __printf(3, 0) struct clk_lookup * __ref
+vclkdev_alloc(struct clk_hw *hw, const char *con_id, const char *dev_fmt,
+	va_list ap)
+{
+	struct clk_lookup_alloc *cla;
+	struct va_format vaf;
+	const char *failure;
+	va_list ap_copy;
+	size_t max_size;
+	ssize_t res;
+
+	cla = kzalloc_obj(*cla);
+	if (!cla)
+		return NULL;
+
+	va_copy(ap_copy, ap);
+
+	cla->cl.clk_hw = hw;
+	if (con_id) {
+		res = strscpy(cla->con_id, con_id, sizeof(cla->con_id));
+		if (res < 0) {
+			max_size = sizeof(cla->con_id);
+			failure = "connection";
+			goto fail;
+		}
+		cla->cl.con_id = cla->con_id;
+	}
+
+	if (dev_fmt) {
+		res = vsnprintf(cla->dev_id, sizeof(cla->dev_id), dev_fmt, ap);
+		if (res >= sizeof(cla->dev_id)) {
+			max_size = sizeof(cla->dev_id);
+			failure = "device";
+			goto fail;
+		}
+		cla->cl.dev_id = cla->dev_id;
+	}
+
+	va_end(ap_copy);
+
+	return &cla->cl;
+
+fail:
+	if (dev_fmt)
+		vaf.fmt = dev_fmt;
+	else
+		vaf.fmt = "null-device";
+	vaf.va = &ap_copy;
+	pr_err("%pV:%s: %s ID is greater than %zu\n",
+	       &vaf, con_id, failure, max_size);
+	va_end(ap_copy);
+
+	/*
+	 * Don't fail in this case, but as the entry won't ever match just
+	 * fill it with something that also won't match.
+	 */
+	strscpy(cla->con_id, "bad", sizeof(cla->con_id));
+	strscpy(cla->dev_id, "bad", sizeof(cla->dev_id));
+
+	return &cla->cl;
+}
+
+static __printf(3, 0) struct clk_lookup *
+vclkdev_create(struct clk_hw *hw, const char *con_id, const char *dev_fmt,
+	va_list ap)
+{
+	struct clk_lookup *cl;
+
+	cl = vclkdev_alloc(hw, con_id, dev_fmt, ap);
+	if (cl)
+		__clkdev_add(cl);
+
+	return cl;
+}
+
+/**
+ * clkdev_create - allocate and add a clkdev lookup structure
+ * @clk: struct clk to associate with all clk_lookups
+ * @con_id: connection ID string on device
+ * @dev_fmt: format string describing device name
+ *
+ * Returns a clk_lookup structure, which can be later unregistered and
+ * freed.
+ */
+struct clk_lookup *clkdev_create(struct clk *clk, const char *con_id,
+	const char *dev_fmt, ...)
+{
+	struct clk_lookup *cl;
+	va_list ap;
+
+	va_start(ap, dev_fmt);
+	cl = vclkdev_create(__clk_get_hw(clk), con_id, dev_fmt, ap);
+	va_end(ap);
+
+	return cl;
+}
+EXPORT_SYMBOL_GPL(clkdev_create);
+
+/**
+ * clkdev_hw_create - allocate and add a clkdev lookup structure
+ * @hw: struct clk_hw to associate with all clk_lookups
+ * @con_id: connection ID string on device
+ * @dev_fmt: format string describing device name
+ *
+ * Returns a clk_lookup structure, which can be later unregistered and
+ * freed.
+ */
+struct clk_lookup *clkdev_hw_create(struct clk_hw *hw, const char *con_id,
+	const char *dev_fmt, ...)
+{
+	struct clk_lookup *cl;
+	va_list ap;
+
+	va_start(ap, dev_fmt);
+	cl = vclkdev_create(hw, con_id, dev_fmt, ap);
+	va_end(ap);
+
+	return cl;
+}
+EXPORT_SYMBOL_GPL(clkdev_hw_create);
+
+int clk_add_alias(const char *alias, const char *alias_dev_name,
+	const char *con_id, struct device *dev)
+{
+	struct clk *r = clk_get(dev, con_id);
+	struct clk_lookup *l;
+
+	if (IS_ERR(r))
+		return PTR_ERR(r);
+
+	l = clkdev_create(r, alias, alias_dev_name ? "%s" : NULL,
+			  alias_dev_name);
+	clk_put(r);
+
+	return l ? 0 : -ENODEV;
+}
+EXPORT_SYMBOL(clk_add_alias);
+
+/*
+ * clkdev_drop - remove a clock dynamically allocated
+ */
+void clkdev_drop(struct clk_lookup *cl)
+{
+	mutex_lock(&clocks_mutex);
+	list_del(&cl->node);
+	mutex_unlock(&clocks_mutex);
+	kfree(cl);
+}
+EXPORT_SYMBOL(clkdev_drop);
+
+static __printf(3, 4) struct clk_lookup *
+__clk_register_clkdev(struct clk_hw *hw, const char *con_id, const char *dev_id, ...)
+{
+	struct clk_lookup *cl;
+	va_list ap;
+
+	va_start(ap, dev_id);
+	cl = vclkdev_create(hw, con_id, dev_id, ap);
+	va_end(ap);
+
+	return cl;
+}
+
+static int do_clk_register_clkdev(struct clk_hw *hw,
+	struct clk_lookup **cl, const char *con_id, const char *dev_id)
+{
+	if (IS_ERR(hw))
+		return PTR_ERR(hw);
+	/*
+	 * Since dev_id can be NULL, and NULL is handled specially, we must
+	 * pass it as either a NULL format string, or with "%s".
+	 */
+	if (dev_id)
+		*cl = __clk_register_clkdev(hw, con_id, "%s", dev_id);
+	else
+		*cl = __clk_register_clkdev(hw, con_id, NULL);
+
+	return *cl ? 0 : -ENOMEM;
+}
+
+/**
+ * clk_register_clkdev - register one clock lookup for a struct clk
+ * @clk: struct clk to associate with all clk_lookups
+ * @con_id: connection ID string on device
+ * @dev_id: string describing device name
+ *
+ * con_id or dev_id may be NULL as a wildcard, just as in the rest of
+ * clkdev.
+ *
+ * To make things easier for mass registration, we detect error clks
+ * from a previous clk_register() call, and return the error code for
+ * those.  This is to permit this function to be called immediately
+ * after clk_register().
+ */
+int clk_register_clkdev(struct clk *clk, const char *con_id,
+	const char *dev_id)
+{
+	struct clk_lookup *cl;
+
+	if (IS_ERR(clk))
+		return PTR_ERR(clk);
+
+	return do_clk_register_clkdev(__clk_get_hw(clk), &cl, con_id,
+					      dev_id);
+}
+EXPORT_SYMBOL(clk_register_clkdev);
+
+/**
+ * clk_hw_register_clkdev - register one clock lookup for a struct clk_hw
+ * @hw: struct clk_hw to associate with all clk_lookups
+ * @con_id: connection ID string on device
+ * @dev_id: format string describing device name
+ *
+ * con_id or dev_id may be NULL as a wildcard, just as in the rest of
+ * clkdev.
+ *
+ * To make things easier for mass registration, we detect error clk_hws
+ * from a previous clk_hw_register_*() call, and return the error code for
+ * those.  This is to permit this function to be called immediately
+ * after clk_hw_register_*().
+ */
+int clk_hw_register_clkdev(struct clk_hw *hw, const char *con_id,
+	const char *dev_id)
+{
+	struct clk_lookup *cl;
+
+	return do_clk_register_clkdev(hw, &cl, con_id, dev_id);
+}
+EXPORT_SYMBOL(clk_hw_register_clkdev);
+
+static void devm_clkdev_release(void *res)
+{
+	clkdev_drop(res);
+}
+
+/**
+ * devm_clk_hw_register_clkdev - managed clk lookup registration for clk_hw
+ * @dev: device this lookup is bound
+ * @hw: struct clk_hw to associate with all clk_lookups
+ * @con_id: connection ID string on device
+ * @dev_id: format string describing device name
+ *
+ * con_id or dev_id may be NULL as a wildcard, just as in the rest of
+ * clkdev.
+ *
+ * To make things easier for mass registration, we detect error clk_hws
+ * from a previous clk_hw_register_*() call, and return the error code for
+ * those.  This is to permit this function to be called immediately
+ * after clk_hw_register_*().
+ */
+int devm_clk_hw_register_clkdev(struct device *dev, struct clk_hw *hw,
+				const char *con_id, const char *dev_id)
+{
+	struct clk_lookup *cl;
+	int rval;
+
+	rval = do_clk_register_clkdev(hw, &cl, con_id, dev_id);
+	if (rval)
+		return rval;
+
+	return devm_add_action_or_reset(dev, devm_clkdev_release, cl);
+}
+EXPORT_SYMBOL(devm_clk_hw_register_clkdev);