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, 76 insertions, 0 deletions

diff --git a/tools/perf/util/block-range.h b/tools/perf/util/block-range.h
new file mode 100644
index 000000000..ec0fb534b
--- /dev/null
+++ b/tools/perf/util/block-range.h
@@ -0,0 +1,76 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_BLOCK_RANGE_H
+#define __PERF_BLOCK_RANGE_H
+
+#include <stdbool.h>
+#include <linux/rbtree.h>
+#include <linux/types.h>
+
+struct symbol;
+
+/*
+ * struct block_range - non-overlapping parts of basic blocks
+ * @node:	treenode
+ * @start:	inclusive start of range
+ * @end:	inclusive end of range
+ * @is_target:	@start is a jump target
+ * @is_branch:	@end is a branch instruction
+ * @coverage:	number of blocks that cover this range
+ * @taken:	number of times the branch is taken (requires @is_branch)
+ * @pred:	number of times the taken branch was predicted
+ */
+struct block_range {
+	struct rb_node node;
+
+	struct symbol *sym;
+
+	u64 start;
+	u64 end;
+
+	int is_target, is_branch;
+
+	u64 coverage;
+	u64 entry;
+	u64 taken;
+	u64 pred;
+};
+
+static inline struct block_range *block_range__next(struct block_range *br)
+{
+	struct rb_node *n = rb_next(&br->node);
+	if (!n)
+		return NULL;
+	return rb_entry(n, struct block_range, node);
+}
+
+struct block_range_iter {
+	struct block_range *start;
+	struct block_range *end;
+};
+
+static inline struct block_range *block_range_iter(struct block_range_iter *iter)
+{
+	return iter->start;
+}
+
+static inline bool block_range_iter__next(struct block_range_iter *iter)
+{
+	if (iter->start == iter->end)
+		return false;
+
+	iter->start = block_range__next(iter->start);
+	return true;
+}
+
+static inline bool block_range_iter__valid(struct block_range_iter *iter)
+{
+	if (!iter->start || !iter->end)
+		return false;
+	return true;
+}
+
+extern struct block_range *block_range__find(u64 addr);
+extern struct block_range_iter block_range__create(u64 start, u64 end);
+extern double block_range__coverage(struct block_range *br);
+
+#endif /* __PERF_BLOCK_RANGE_H */