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, 41 insertions, 0 deletions

diff --git a/tools/perf/util/stream.h b/tools/perf/util/stream.h
new file mode 100644
index 000000000..50f7e6e04
--- /dev/null
+++ b/tools/perf/util/stream.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_STREAM_H
+#define __PERF_STREAM_H
+
+struct callchain_node;
+struct evlist;
+struct evsel;
+
+struct stream {
+	struct callchain_node	*cnode;
+	struct callchain_node	*pair_cnode;
+};
+
+struct evsel_streams {
+	struct stream		*streams;
+	const struct evsel	*evsel;
+	int			nr_streams_max;
+	int			nr_streams;
+	u64			streams_hits;
+};
+
+struct evlist_streams {
+	struct evsel_streams	*ev_streams;
+	int			nr_evsel;
+};
+
+void evlist_streams__delete(struct evlist_streams *els);
+
+struct evlist_streams *evlist__create_streams(struct evlist *evlist,
+					      int nr_streams_max);
+
+struct evsel_streams *evsel_streams__entry(struct evlist_streams *els,
+					   const struct evsel *evsel);
+
+void evsel_streams__match(struct evsel_streams *es_base,
+			  struct evsel_streams *es_pair);
+
+void evsel_streams__report(struct evsel_streams *es_base,
+			   struct evsel_streams *es_pair);
+
+#endif /* __PERF_STREAM_H */