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, 116 insertions, 0 deletions

diff --git a/tools/perf/util/tool.h b/tools/perf/util/tool.h
new file mode 100644
index 000000000..2a4f124ff
--- /dev/null
+++ b/tools/perf/util/tool.h
@@ -0,0 +1,116 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_TOOL_H
+#define __PERF_TOOL_H
+
+#include <stdbool.h>
+
+#include <linux/types.h>
+
+struct perf_session;
+union perf_event;
+struct evlist;
+struct perf_sample;
+struct perf_tool;
+struct machine;
+struct ordered_events;
+
+typedef int (*event_sample)(const struct perf_tool *tool, union perf_event *event,
+			    struct perf_sample *sample,
+			    struct machine *machine);
+
+typedef int (*event_op)(const struct perf_tool *tool, union perf_event *event,
+			struct perf_sample *sample, struct machine *machine);
+
+typedef int (*event_attr_op)(const struct perf_tool *tool,
+			     union perf_event *event,
+			     struct evlist **pevlist);
+
+typedef int (*event_op2)(const struct perf_tool *tool, struct perf_session *session,
+			 union perf_event *event);
+typedef s64 (*event_op3)(const struct perf_tool *tool, struct perf_session *session,
+			 union perf_event *event);
+typedef int (*event_op4)(const struct perf_tool *tool, struct perf_session *session,
+			 union perf_event *event, u64 data, const char *str);
+
+typedef int (*event_oe)(const struct perf_tool *tool, union perf_event *event,
+			struct ordered_events *oe);
+
+enum show_feature_header {
+	SHOW_FEAT_NO_HEADER = 0,
+	SHOW_FEAT_HEADER,
+	SHOW_FEAT_HEADER_FULL_INFO,
+};
+
+struct perf_tool {
+	event_sample	sample,
+			read,
+			callchain_deferred;
+	event_op	mmap,
+			mmap2,
+			comm,
+			namespaces,
+			cgroup,
+			fork,
+			exit,
+			lost,
+			lost_samples,
+			aux,
+			itrace_start,
+			aux_output_hw_id,
+			context_switch,
+			throttle,
+			unthrottle,
+			ksymbol,
+			bpf,
+			text_poke;
+
+	event_attr_op	attr;
+	event_attr_op	event_update;
+	event_op2	tracing_data;
+	event_oe	finished_round;
+	event_op2	build_id,
+			id_index,
+			auxtrace_info,
+			auxtrace_error,
+			time_conv,
+			thread_map,
+			cpu_map,
+			stat_config,
+			stat,
+			stat_round,
+			feature,
+			finished_init,
+			bpf_metadata,
+			schedstat_cpu,
+			schedstat_domain;
+	event_op4	compressed;
+	event_op3	auxtrace;
+	bool		ordered_events;
+	bool		ordering_requires_timestamps;
+	bool		namespace_events;
+	bool		cgroup_events;
+	bool		no_warn;
+	bool		dont_split_sample_group;
+	bool		merge_deferred_callchains;
+	enum show_feature_header show_feat_hdr;
+};
+
+void perf_tool__init(struct perf_tool *tool, bool ordered_events);
+
+bool perf_tool__compressed_is_stub(const struct perf_tool *tool);
+
+int process_event_sample_stub(const struct perf_tool *tool,
+			      union perf_event *event,
+			      struct perf_sample *sample,
+			      struct machine *machine);
+
+struct delegate_tool {
+	/** @tool: The actual tool that calls the delegate. */
+	struct perf_tool tool;
+	/** @delegate: The tool that is delegated to. */
+	struct perf_tool *delegate;
+};
+
+void delegate_tool__init(struct delegate_tool *tool, struct perf_tool *delegate);
+
+#endif /* __PERF_TOOL_H */