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-info.h b/tools/perf/util/block-info.h
new file mode 100644
index 000000000..b9329dc3a
--- /dev/null
+++ b/tools/perf/util/block-info.h
@@ -0,0 +1,76 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_BLOCK_H
+#define __PERF_BLOCK_H
+
+#include <linux/types.h>
+#include "hist.h"
+#include "symbol.h"
+#include "sort.h"
+#include "ui/ui.h"
+
+struct block_info {
+	struct symbol		*sym;
+	u64			start;
+	u64			end;
+	u64			cycles;
+	u64			cycles_aggr;
+	s64			cycles_spark[NUM_SPARKS];
+	u64			total_cycles;
+	int			num;
+	int			num_aggr;
+	int			br_cntr_nr;
+	u64			*br_cntr;
+	struct evsel		*evsel;
+};
+
+struct block_fmt {
+	struct perf_hpp_fmt	fmt;
+	int			idx;
+	int			width;
+	const char		*header;
+	u64			total_cycles;
+	u64			block_cycles;
+};
+
+enum {
+	PERF_HPP_REPORT__BLOCK_TOTAL_CYCLES_PCT,
+	PERF_HPP_REPORT__BLOCK_LBR_CYCLES,
+	PERF_HPP_REPORT__BLOCK_CYCLES_PCT,
+	PERF_HPP_REPORT__BLOCK_AVG_CYCLES,
+	PERF_HPP_REPORT__BLOCK_RANGE,
+	PERF_HPP_REPORT__BLOCK_DSO,
+	PERF_HPP_REPORT__BLOCK_BRANCH_COUNTER,
+	PERF_HPP_REPORT__BLOCK_MAX_INDEX
+};
+
+struct block_report {
+	struct block_hist	hist;
+	u64			cycles;
+	struct block_fmt	fmts[PERF_HPP_REPORT__BLOCK_MAX_INDEX];
+	int			nr_fmts;
+};
+
+void block_info__delete(struct block_info *bi);
+
+int64_t __block_info__cmp(struct hist_entry *left, struct hist_entry *right);
+
+int64_t block_info__cmp(struct perf_hpp_fmt *fmt __maybe_unused,
+			struct hist_entry *left, struct hist_entry *right);
+
+int block_info__process_sym(struct hist_entry *he, struct block_hist *bh,
+			    u64 *block_cycles_aggr, u64 total_cycles,
+			    unsigned int br_cntr_nr);
+
+struct block_report *block_info__create_report(struct evlist *evlist,
+					       u64 total_cycles,
+					       int *block_hpps, int nr_hpps,
+					       int *nr_reps);
+
+void block_info__free_report(struct block_report *reps, int nr_reps);
+
+int report__browse_block_hists(struct block_hist *bh, float min_percent,
+			       struct evsel *evsel, struct perf_env *env);
+
+float block_info__total_cycles_percent(struct hist_entry *he);
+
+#endif /* __PERF_BLOCK_H */