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, 218 insertions, 0 deletions

diff --git a/tools/perf/util/session.h b/tools/perf/util/session.h
new file mode 100644
index 000000000..d554e2a1a
--- /dev/null
+++ b/tools/perf/util/session.h
@@ -0,0 +1,218 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_SESSION_H
+#define __PERF_SESSION_H
+
+#include "trace-event.h"
+#include "event.h"
+#include "header.h"
+#include "machine.h"
+#include "data.h"
+#include "ordered-events.h"
+#include "util/compress.h"
+#include <linux/kernel.h>
+#include <linux/rbtree.h>
+#include <linux/perf_event.h>
+
+struct ip_callchain;
+struct symbol;
+struct thread;
+
+struct auxtrace;
+struct itrace_synth_opts;
+
+struct decomp_data {
+	struct decomp	 *decomp;
+	struct decomp	 *decomp_last;
+	struct zstd_data *zstd_decomp;
+};
+
+/**
+ * struct perf_session- A Perf session holds the main state when the program is
+ * working with live perf events or reading data from an input file.
+ *
+ * The rough organization of a perf_session is:
+ * ```
+ * +--------------+           +-----------+           +------------+
+ * |   Session    |1..* ----->|  Machine  |1..* ----->|   Thread   |
+ * +--------------+           +-----------+           +------------+
+ * ```
+ */
+struct perf_session {
+	/**
+	 * @header: The read version of a perf_file_header, or captures global
+	 * information from a live session.
+	 */
+	struct perf_header	header;
+	/** @machines: Machines within the session a host and 0 or more guests. */
+	struct machines		machines;
+	/** @evlist: List of evsels/events of the session. */
+	struct evlist	*evlist;
+	/** @auxtrace: callbacks to allow AUX area data decoding. */
+	const struct auxtrace	*auxtrace;
+	/** @itrace_synth_opts: AUX area tracing synthesis options. */
+	struct itrace_synth_opts *itrace_synth_opts;
+	/** @auxtrace_index: index of AUX area tracing events within a perf.data file. */
+	struct list_head	auxtrace_index;
+#ifdef HAVE_LIBTRACEEVENT
+	/** @tevent: handles for libtraceevent and plugins. */
+	struct trace_event	tevent;
+#endif
+	/** @time_conv: Holds contents of last PERF_RECORD_TIME_CONV event. */
+	struct perf_record_time_conv	time_conv;
+	/** @trace_event_repipe: When set causes read trace events to be written to stdout. */
+	bool			trace_event_repipe;
+	/**
+	 * @one_mmap: The reader will use a single mmap by default. There may be
+	 * multiple data files in particular for aux events. If this is true
+	 * then the single big mmap for the data file can be assumed.
+	 */
+	bool			one_mmap;
+	/** @one_mmap_addr: Address of initial perf data file reader mmap. */
+	void			*one_mmap_addr;
+	/** @one_mmap_offset: File offset in perf.data file when mapped. */
+	u64			one_mmap_offset;
+	/** @one_mmap_size: Size of the single mmap in bytes. */
+	u64			one_mmap_size;
+	/** @ordered_events: Used to turn unordered events into ordered ones. */
+	struct ordered_events	ordered_events;
+	/** @data: Optional perf data file being read from. */
+	struct perf_data	*data;
+	/** @tool: callbacks for event handling. */
+	const struct perf_tool	*tool;
+	/**
+	 * @bytes_transferred: Used by perf record to count written bytes before
+	 * compression.
+	 */
+	u64			bytes_transferred;
+	/**
+	 * @bytes_compressed: Used by perf record to count written bytes after
+	 * compression.
+	 */
+	u64			bytes_compressed;
+	/** @zstd_data: Owner of global compression state, buffers, etc. */
+	struct zstd_data	zstd_data;
+	struct decomp_data	decomp_data;
+	struct decomp_data	*active_decomp;
+};
+
+struct decomp {
+	struct decomp *next;
+	u64 file_pos;
+	const char *file_path;
+	size_t mmap_len;
+	u64 head;
+	size_t size;
+	char data[];
+};
+
+struct perf_tool;
+
+struct perf_session *__perf_session__new(struct perf_data *data,
+					 struct perf_tool *tool,
+					 bool trace_event_repipe,
+					 struct perf_env *host_env);
+
+static inline struct perf_session *perf_session__new(struct perf_data *data,
+						     struct perf_tool *tool)
+{
+	return __perf_session__new(data, tool, /*trace_event_repipe=*/false, /*host_env=*/NULL);
+}
+
+void perf_session__delete(struct perf_session *session);
+
+void perf_event_header__bswap(struct perf_event_header *hdr);
+
+int perf_session__peek_event(struct perf_session *session, off_t file_offset,
+			     void *buf, size_t buf_sz,
+			     union perf_event **event_ptr,
+			     struct perf_sample *sample);
+typedef int (*peek_events_cb_t)(struct perf_session *session,
+				union perf_event *event, u64 offset,
+				void *data);
+int perf_session__peek_events(struct perf_session *session, u64 offset,
+			      u64 size, peek_events_cb_t cb, void *data);
+
+int perf_session__process_events(struct perf_session *session);
+
+int perf_session__queue_event(struct perf_session *s, union perf_event *event,
+			      u64 timestamp, u64 file_offset, const char *file_path);
+
+int perf_session__resolve_callchain(struct perf_session *session,
+				    struct evsel *evsel,
+				    struct thread *thread,
+				    struct ip_callchain *chain,
+				    struct symbol **parent);
+
+bool perf_session__has_traces(struct perf_session *session, const char *msg);
+bool perf_session__has_switch_events(struct perf_session *session);
+
+void perf_event__attr_swap(struct perf_event_attr *attr);
+
+int perf_session__create_kernel_maps(struct perf_session *session);
+
+void perf_session__set_id_hdr_size(struct perf_session *session);
+
+static inline
+struct machine *perf_session__find_machine(struct perf_session *session, pid_t pid)
+{
+	return machines__find(&session->machines, pid);
+}
+
+static inline
+struct machine *perf_session__findnew_machine(struct perf_session *session, pid_t pid)
+{
+	return machines__findnew(&session->machines, pid);
+}
+
+struct thread *perf_session__findnew(struct perf_session *session, pid_t pid);
+int perf_session__register_idle_thread(struct perf_session *session);
+
+size_t perf_session__fprintf(struct perf_session *session, FILE *fp);
+
+size_t perf_session__fprintf_dsos(struct perf_session *session, FILE *fp);
+
+size_t perf_session__fprintf_dsos_buildid(struct perf_session *session, FILE *fp,
+					  bool (fn)(struct dso *dso, int parm), int parm);
+
+size_t perf_session__fprintf_nr_events(struct perf_session *session, FILE *fp);
+
+void perf_session__dump_kmaps(struct perf_session *session);
+
+struct evsel *perf_session__find_first_evtype(struct perf_session *session,
+					    unsigned int type);
+
+int perf_session__cpu_bitmap(struct perf_session *session,
+			     const char *cpu_list, unsigned long *cpu_bitmap);
+
+void perf_session__fprintf_info(struct perf_session *s, FILE *fp, bool full);
+
+struct evsel_str_handler;
+
+#define perf_session__set_tracepoints_handlers(session, array) \
+	__evlist__set_tracepoints_handlers(session->evlist, array, ARRAY_SIZE(array))
+
+extern volatile int session_done;
+
+#define session_done()	READ_ONCE(session_done)
+
+int perf_session__deliver_synth_event(struct perf_session *session,
+				      union perf_event *event,
+				      struct perf_sample *sample);
+int perf_session__deliver_synth_attr_event(struct perf_session *session,
+					   const struct perf_event_attr *attr,
+					   u64 id);
+
+int perf_session__dsos_hit_all(struct perf_session *session);
+
+int perf_event__process_id_index(const struct perf_tool *tool,
+				 struct perf_session *session,
+				 union perf_event *event);
+
+int perf_event__process_finished_round(const struct perf_tool *tool,
+				       union perf_event *event,
+				       struct ordered_events *oe);
+
+struct perf_env *perf_session__env(struct perf_session *session);
+uint16_t perf_session__e_machine(struct perf_session *session, uint32_t *e_flags);
+
+#endif /* __PERF_SESSION_H */