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, 325 insertions, 0 deletions

diff --git a/drivers/of/resolver.c b/drivers/of/resolver.c
new file mode 100644
index 000000000..86424e145
--- /dev/null
+++ b/drivers/of/resolver.c
@@ -0,0 +1,325 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Functions for dealing with DT resolution
+ *
+ * Copyright (C) 2012 Pantelis Antoniou <panto@antoniou-consulting.com>
+ * Copyright (C) 2012 Texas Instruments Inc.
+ */
+
+#define pr_fmt(fmt)	"OF: resolver: " fmt
+
+#include <linux/cleanup.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/string.h>
+#include <linux/ctype.h>
+#include <linux/errno.h>
+#include <linux/slab.h>
+
+#include "of_private.h"
+
+static phandle live_tree_max_phandle(void)
+{
+	struct device_node *node;
+	phandle phandle;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&devtree_lock, flags);
+	phandle = 0;
+	for_each_of_allnodes(node) {
+		if (node->phandle != OF_PHANDLE_ILLEGAL &&
+				node->phandle > phandle)
+			phandle = node->phandle;
+	}
+	raw_spin_unlock_irqrestore(&devtree_lock, flags);
+
+	return phandle;
+}
+
+static void adjust_overlay_phandles(struct device_node *overlay,
+		int phandle_delta)
+{
+	struct device_node *child;
+	const struct property *prop;
+	phandle phandle;
+
+	/* adjust node's phandle in node */
+	if (overlay->phandle != 0 && overlay->phandle != OF_PHANDLE_ILLEGAL)
+		overlay->phandle += phandle_delta;
+
+	/* copy adjusted phandle into *phandle properties */
+	for_each_property_of_node(overlay, prop) {
+
+		if (of_prop_cmp(prop->name, "phandle") &&
+		    of_prop_cmp(prop->name, "linux,phandle"))
+			continue;
+
+		if (prop->length < 4)
+			continue;
+
+		phandle = be32_to_cpup(prop->value);
+		if (phandle == OF_PHANDLE_ILLEGAL)
+			continue;
+
+		*(__be32 *)prop->value = cpu_to_be32(overlay->phandle);
+	}
+
+	for_each_child_of_node(overlay, child)
+		adjust_overlay_phandles(child, phandle_delta);
+}
+
+static int update_usages_of_a_phandle_reference(struct device_node *overlay,
+		const struct property *prop_fixup, phandle phandle)
+{
+	struct device_node *refnode;
+	const struct property *prop;
+	char *value __free(kfree) = kmemdup(prop_fixup->value, prop_fixup->length, GFP_KERNEL);
+	char *cur, *end, *node_path, *prop_name, *s;
+	int offset, len;
+	int err = 0;
+
+	if (!value)
+		return -ENOMEM;
+
+	/* prop_fixup contains a list of tuples of path:property_name:offset */
+	end = value + prop_fixup->length;
+	for (cur = value; cur < end; cur += len + 1) {
+		len = strlen(cur);
+
+		node_path = cur;
+		s = strchr(cur, ':');
+		if (!s)
+			return -EINVAL;
+		*s++ = '\0';
+
+		prop_name = s;
+		s = strchr(s, ':');
+		if (!s)
+			return -EINVAL;
+		*s++ = '\0';
+
+		err = kstrtoint(s, 10, &offset);
+		if (err)
+			return err;
+
+		refnode = __of_find_node_by_full_path(of_node_get(overlay), node_path);
+		if (!refnode)
+			continue;
+
+		for_each_property_of_node(refnode, prop) {
+			if (!of_prop_cmp(prop->name, prop_name))
+				break;
+		}
+		of_node_put(refnode);
+
+		if (!prop)
+			return -ENOENT;
+
+		if (offset < 0 || offset + sizeof(__be32) > prop->length)
+			return -EINVAL;
+
+		*(__be32 *)(prop->value + offset) = cpu_to_be32(phandle);
+	}
+
+	return 0;
+}
+
+/* compare nodes taking into account that 'name' strips out the @ part */
+static int node_name_cmp(const struct device_node *dn1,
+		const struct device_node *dn2)
+{
+	const char *n1 = kbasename(dn1->full_name);
+	const char *n2 = kbasename(dn2->full_name);
+
+	return of_node_cmp(n1, n2);
+}
+
+/*
+ * Adjust the local phandle references by the given phandle delta.
+ *
+ * Subtree @local_fixups, which is overlay node __local_fixups__,
+ * mirrors the fragment node structure at the root of the overlay.
+ *
+ * For each property in the fragments that contains a phandle reference,
+ * @local_fixups has a property of the same name that contains a list
+ * of offsets of the phandle reference(s) within the respective property
+ * value(s).  The values at these offsets will be fixed up.
+ */
+static int adjust_local_phandle_references(const struct device_node *local_fixups,
+		const struct device_node *overlay, int phandle_delta)
+{
+	struct device_node *overlay_child;
+	const struct property *prop_fix, *prop;
+	int err, i, count;
+	unsigned int off;
+
+	if (!local_fixups)
+		return 0;
+
+	for_each_property_of_node(local_fixups, prop_fix) {
+
+		/* skip properties added automatically */
+		if (is_pseudo_property(prop_fix->name))
+			continue;
+
+		if ((prop_fix->length % 4) != 0 || prop_fix->length == 0)
+			return -EINVAL;
+		count = prop_fix->length / sizeof(__be32);
+
+		for_each_property_of_node(overlay, prop) {
+			if (!of_prop_cmp(prop->name, prop_fix->name))
+				break;
+		}
+
+		if (!prop)
+			return -EINVAL;
+
+		for (i = 0; i < count; i++) {
+			off = be32_to_cpu(((__be32 *)prop_fix->value)[i]);
+			if ((off + 4) > prop->length)
+				return -EINVAL;
+
+			be32_add_cpu(prop->value + off, phandle_delta);
+		}
+	}
+
+	/*
+	 * These nested loops recurse down two subtrees in parallel, where the
+	 * node names in the two subtrees match.
+	 *
+	 * The roots of the subtrees are the overlay's __local_fixups__ node
+	 * and the overlay's root node.
+	 */
+	for_each_child_of_node_scoped(local_fixups, child) {
+
+		for_each_child_of_node(overlay, overlay_child)
+			if (!node_name_cmp(child, overlay_child)) {
+				of_node_put(overlay_child);
+				break;
+			}
+
+		if (!overlay_child)
+			return -EINVAL;
+
+		err = adjust_local_phandle_references(child, overlay_child,
+				phandle_delta);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+/**
+ * of_resolve_phandles - Relocate and resolve overlay against live tree
+ *
+ * @overlay:	Pointer to devicetree overlay to relocate and resolve
+ *
+ * Modify (relocate) values of local phandles in @overlay to a range that
+ * does not conflict with the live expanded devicetree.  Update references
+ * to the local phandles in @overlay.  Update (resolve) phandle references
+ * in @overlay that refer to the live expanded devicetree.
+ *
+ * Phandle values in the live tree are in the range of
+ * 1 .. live_tree_max_phandle().  The range of phandle values in the overlay
+ * also begin with at 1.  Adjust the phandle values in the overlay to begin
+ * at live_tree_max_phandle() + 1.  Update references to the phandles to
+ * the adjusted phandle values.
+ *
+ * The name of each property in the "__fixups__" node in the overlay matches
+ * the name of a symbol (a label) in the live tree.  The values of each
+ * property in the "__fixups__" node is a list of the property values in the
+ * overlay that need to be updated to contain the phandle reference
+ * corresponding to that symbol in the live tree.  Update the references in
+ * the overlay with the phandle values in the live tree.
+ *
+ * @overlay must be detached.
+ *
+ * Resolving and applying @overlay to the live expanded devicetree must be
+ * protected by a mechanism to ensure that multiple overlays are processed
+ * in a single threaded manner so that multiple overlays will not relocate
+ * phandles to overlapping ranges.  The mechanism to enforce this is not
+ * yet implemented.
+ *
+ * Return: %0 on success or a negative error value on error.
+ */
+int of_resolve_phandles(struct device_node *overlay)
+{
+	struct device_node *child, *refnode;
+	struct device_node *overlay_fixups;
+	struct device_node __free(device_node) *local_fixups = NULL;
+	struct property *prop;
+	const char *refpath;
+	phandle phandle, phandle_delta;
+	int err;
+
+	if (!overlay) {
+		pr_err("null overlay\n");
+		return -EINVAL;
+	}
+
+	if (!of_node_check_flag(overlay, OF_DETACHED)) {
+		pr_err("overlay not detached\n");
+		return -EINVAL;
+	}
+
+	phandle_delta = live_tree_max_phandle() + 1;
+	adjust_overlay_phandles(overlay, phandle_delta);
+
+	for_each_child_of_node(overlay, local_fixups)
+		if (of_node_name_eq(local_fixups, "__local_fixups__"))
+			break;
+
+	err = adjust_local_phandle_references(local_fixups, overlay, phandle_delta);
+	if (err)
+		return err;
+
+	overlay_fixups = NULL;
+
+	for_each_child_of_node(overlay, child) {
+		if (of_node_name_eq(child, "__fixups__"))
+			overlay_fixups = child;
+	}
+
+	if (!overlay_fixups)
+		return 0;
+
+	struct device_node __free(device_node) *tree_symbols = of_find_node_by_path("/__symbols__");
+	if (!tree_symbols) {
+		pr_err("no symbols in root of device tree.\n");
+		return -EINVAL;
+	}
+
+	for_each_property_of_node(overlay_fixups, prop) {
+
+		/* skip properties added automatically */
+		if (!of_prop_cmp(prop->name, "name"))
+			continue;
+
+		err = of_property_read_string(tree_symbols,
+				prop->name, &refpath);
+		if (err) {
+			pr_err("node label '%s' not found in live devicetree symbols table\n",
+			       prop->name);
+			return err;
+		}
+
+		refnode = of_find_node_by_path(refpath);
+		if (!refnode)
+			return -ENOENT;
+
+		phandle = refnode->phandle;
+		of_node_put(refnode);
+
+		err = update_usages_of_a_phandle_reference(overlay, prop, phandle);
+		if (err)
+			break;
+	}
+
+	if (err)
+		pr_err("overlay phandle fixup failed: %d\n", err);
+	return err;
+}
+EXPORT_SYMBOL_GPL(of_resolve_phandles);