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, 66 insertions, 0 deletions

diff --git a/tools/perf/util/top.h b/tools/perf/util/top.h
new file mode 100644
index 000000000..04ff92684
--- /dev/null
+++ b/tools/perf/util/top.h
@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_TOP_H
+#define __PERF_TOP_H 1
+
+#include "tool.h"
+#include "evswitch.h"
+#include "annotate.h"
+#include "mutex.h"
+#include "ordered-events.h"
+#include "record.h"
+#include <linux/types.h>
+#include <stddef.h>
+#include <stdbool.h>
+#include <sys/ioctl.h>
+
+struct evlist;
+struct evsel;
+struct perf_session;
+
+struct perf_top {
+	struct perf_tool   tool;
+	struct evlist *evlist, *sb_evlist;
+	struct record_opts record_opts;
+	struct evswitch	   evswitch;
+	/*
+	 * Symbols will be added here in perf_event__process_sample and will
+	 * get out after decayed.
+	 */
+	u64		   samples, lost, lost_total, drop, drop_total;
+	u64		   kernel_samples, us_samples;
+	u64		   exact_samples;
+	u64		   guest_us_samples, guest_kernel_samples;
+	int		   print_entries, count_filter, delay_secs;
+	int		   max_stack;
+	bool		   hide_kernel_symbols, hide_user_symbols, zero;
+#ifdef HAVE_SLANG_SUPPORT
+	bool		   use_tui;
+#endif
+	bool		   use_stdio;
+	bool		   vmlinux_warned;
+	bool		   dump_symtab;
+	bool		   stitch_lbr;
+	struct hist_entry  *sym_filter_entry;
+	struct evsel 	   *sym_evsel;
+	struct perf_session *session;
+	struct winsize	   winsize;
+	int		   realtime_prio;
+	const char	   *sym_filter;
+	float		   min_percent;
+	unsigned int	   nr_threads_synthesize;
+	const char	   *uid_str;
+
+	struct {
+		struct ordered_events	*in;
+		struct ordered_events	 data[2];
+		bool			 rotate;
+		struct mutex mutex;
+		struct cond cond;
+	} qe;
+};
+
+#define CONSOLE_CLEAR ""
+
+size_t perf_top__header_snprintf(struct perf_top *top, char *bf, size_t size);
+void perf_top__reset_sample_counters(struct perf_top *top);
+#endif /* __PERF_TOP_H */