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, 98 insertions, 0 deletions

diff --git a/scripts/include/hashtable.h b/scripts/include/hashtable.h
new file mode 100644
index 000000000..45abcb12b
--- /dev/null
+++ b/scripts/include/hashtable.h
@@ -0,0 +1,98 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef HASHTABLE_H
+#define HASHTABLE_H
+
+#include "array_size.h"
+#include "list.h"
+
+#define HASH_SIZE(name) (ARRAY_SIZE(name))
+
+#define HASHTABLE_DECLARE(name, size)		struct hlist_head name[size]
+
+#define HASHTABLE_DEFINE(name, size)						\
+	HASHTABLE_DECLARE(name, size) =						\
+			{ [0 ... ((size) - 1)] = HLIST_HEAD_INIT }
+
+#define hash_head(table, key)		(&(table)[(key) % HASH_SIZE(table)])
+
+static inline void __hash_init(struct hlist_head *ht, unsigned int sz)
+{
+	unsigned int i;
+
+	for (i = 0; i < sz; i++)
+		INIT_HLIST_HEAD(&ht[i]);
+}
+
+/**
+ * hash_init - initialize a hash table
+ * @table: hashtable to be initialized
+ *
+ * This has to be a macro since HASH_SIZE() will not work on pointers since
+ * it calculates the size during preprocessing.
+ */
+#define hash_init(table) __hash_init(table, HASH_SIZE(table))
+
+/**
+ * hash_add - add an object to a hashtable
+ * @table: hashtable to add to
+ * @node: the &struct hlist_node of the object to be added
+ * @key: the key of the object to be added
+ */
+#define hash_add(table, node, key)						\
+	hlist_add_head(node, hash_head(table, key))
+
+/**
+ * hash_del - remove an object from a hashtable
+ * @node: &struct hlist_node of the object to remove
+ */
+static inline void hash_del(struct hlist_node *node)
+{
+	hlist_del_init(node);
+}
+
+/**
+ * hash_for_each - iterate over a hashtable
+ * @table: hashtable to iterate
+ * @obj: the type * to use as a loop cursor for each entry
+ * @member: the name of the hlist_node within the struct
+ */
+#define hash_for_each(table, obj, member)				\
+	for (int _bkt = 0; _bkt < HASH_SIZE(table); _bkt++)		\
+		hlist_for_each_entry(obj, &table[_bkt], member)
+
+/**
+ * hash_for_each_safe - iterate over a hashtable safe against removal of
+ * hash entry
+ * @table: hashtable to iterate
+ * @obj: the type * to use as a loop cursor for each entry
+ * @tmp: a &struct hlist_node used for temporary storage
+ * @member: the name of the hlist_node within the struct
+ */
+#define hash_for_each_safe(table, obj, tmp, member)			\
+	for (int _bkt = 0; _bkt < HASH_SIZE(table); _bkt++)		\
+		hlist_for_each_entry_safe(obj, tmp, &table[_bkt], member)
+
+/**
+ * hash_for_each_possible - iterate over all possible objects hashing to the
+ * same bucket
+ * @table: hashtable to iterate
+ * @obj: the type * to use as a loop cursor for each entry
+ * @member: the name of the hlist_node within the struct
+ * @key: the key of the objects to iterate over
+ */
+#define hash_for_each_possible(table, obj, member, key)			\
+	hlist_for_each_entry(obj, hash_head(table, key), member)
+
+/**
+ * hash_for_each_possible_safe - iterate over all possible objects hashing to the
+ * same bucket safe against removals
+ * @table: hashtable to iterate
+ * @obj: the type * to use as a loop cursor for each entry
+ * @tmp: a &struct hlist_node used for temporary storage
+ * @member: the name of the hlist_node within the struct
+ * @key: the key of the objects to iterate over
+ */
+#define hash_for_each_possible_safe(table, obj, tmp, member, key)	\
+	hlist_for_each_entry_safe(obj, tmp, hash_head(table, key), member)
+
+#endif /* HASHTABLE_H */