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, 461 insertions, 0 deletions

diff --git a/tools/perf/util/data-convert-json.c b/tools/perf/util/data-convert-json.c
new file mode 100644
index 000000000..40412c3db
--- /dev/null
+++ b/tools/perf/util/data-convert-json.c
@@ -0,0 +1,461 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * JSON export.
+ *
+ * Copyright (C) 2021, CodeWeavers Inc. <nfraser@codeweavers.com>
+ */
+
+#include "data-convert.h"
+
+#include <fcntl.h>
+#include <inttypes.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include "linux/compiler.h"
+#include "linux/err.h"
+#include "util/auxtrace.h"
+#include "util/debug.h"
+#include "util/env.h"
+#include "util/dso.h"
+#include "util/event.h"
+#include "util/evsel.h"
+#include "util/evlist.h"
+#include "util/header.h"
+#include "util/map.h"
+#include "util/session.h"
+#include "util/symbol.h"
+#include "util/thread.h"
+#include "util/time-utils.h"
+#include "util/tool.h"
+
+#ifdef HAVE_LIBTRACEEVENT
+#include <event-parse.h>
+#endif
+
+struct convert_json {
+	struct perf_tool tool;
+	FILE *out;
+	bool first;
+	struct perf_time_interval *ptime_range;
+	int range_size;
+	int range_num;
+
+	u64 events_count;
+	u64 skipped;
+};
+
+// Outputs a JSON-encoded string surrounded by quotes with characters escaped.
+static void output_json_string(FILE *out, const char *s)
+{
+	fputc('"', out);
+	if (!s)
+		goto out;
+
+	while (*s) {
+		switch (*s) {
+
+		// required escapes with special forms as per RFC 8259
+		case '"':  fputs("\\\"", out); break;
+		case '\\': fputs("\\\\", out); break;
+		case '\b': fputs("\\b", out);  break;
+		case '\f': fputs("\\f", out);  break;
+		case '\n': fputs("\\n", out);  break;
+		case '\r': fputs("\\r", out);  break;
+		case '\t': fputs("\\t", out);  break;
+
+		default:
+			// all other control characters must be escaped by hex code
+			if (*s <= 0x1f)
+				fprintf(out, "\\u%04x", *s);
+			else
+				fputc(*s, out);
+			break;
+		}
+
+		++s;
+	}
+out:
+	fputc('"', out);
+}
+
+// Outputs an optional comma, newline and indentation to delimit a new value
+// from the previous one in a JSON object or array.
+static void output_json_delimiters(FILE *out, bool comma, int depth)
+{
+	int i;
+
+	if (comma)
+		fputc(',', out);
+	fputc('\n', out);
+	for (i = 0; i < depth; ++i)
+		fputc('\t', out);
+}
+
+// Outputs a printf format string (with delimiter) as a JSON value.
+__printf(4, 5)
+static void output_json_format(FILE *out, bool comma, int depth, const char *format, ...)
+{
+	va_list args;
+
+	output_json_delimiters(out, comma, depth);
+	va_start(args, format);
+	vfprintf(out,  format, args);
+	va_end(args);
+}
+
+// Outputs a JSON key-value pair where the value is a string.
+static void output_json_key_string(FILE *out, bool comma, int depth,
+		const char *key, const char *value)
+{
+	output_json_delimiters(out, comma, depth);
+	output_json_string(out, key);
+	fputs(": ", out);
+	output_json_string(out, value);
+}
+
+// Outputs a JSON key-value pair where the value is a printf format string.
+__printf(5, 6)
+static void output_json_key_format(FILE *out, bool comma, int depth,
+		const char *key, const char *format, ...)
+{
+	va_list args;
+
+	output_json_delimiters(out, comma, depth);
+	output_json_string(out, key);
+	fputs(": ", out);
+	va_start(args, format);
+	vfprintf(out,  format, args);
+	va_end(args);
+}
+
+static void output_sample_callchain_entry(const struct perf_tool *tool,
+		u64 ip, struct addr_location *al)
+{
+	struct convert_json *c = container_of(tool, struct convert_json, tool);
+	FILE *out = c->out;
+
+	output_json_format(out, false, 4, "{");
+	output_json_key_format(out, false, 5, "ip", "\"0x%" PRIx64 "\"", ip);
+
+	if (al && al->sym && al->sym->namelen) {
+		struct dso *dso = al->map ? map__dso(al->map) : NULL;
+
+		fputc(',', out);
+		output_json_key_string(out, false, 5, "symbol", al->sym->name);
+
+		if (dso) {
+			const char *dso_name = dso__short_name(dso);
+
+			if (dso_name && strlen(dso_name) > 0) {
+				fputc(',', out);
+				output_json_key_string(out, false, 5, "dso", dso_name);
+			}
+		}
+	}
+
+	output_json_format(out, false, 4, "}");
+}
+
+static int process_sample_event(const struct perf_tool *tool,
+				union perf_event *event __maybe_unused,
+				struct perf_sample *sample,
+				struct machine *machine)
+{
+	struct convert_json *c = container_of(tool, struct convert_json, tool);
+	FILE *out = c->out;
+	struct addr_location al;
+	u64 sample_type = __evlist__combined_sample_type(sample->evsel->evlist);
+	u8 cpumode = PERF_RECORD_MISC_USER;
+
+	addr_location__init(&al);
+	if (machine__resolve(machine, &al, sample) < 0) {
+		pr_err("Sample resolution failed!\n");
+		addr_location__exit(&al);
+		return -1;
+	}
+
+	if (perf_time__ranges_skip_sample(c->ptime_range, c->range_num, sample->time)) {
+		++c->skipped;
+		addr_location__exit(&al);
+		return 0;
+	}
+
+	++c->events_count;
+
+	if (c->first)
+		c->first = false;
+	else
+		fputc(',', out);
+	output_json_format(out, false, 2, "{");
+
+	output_json_key_format(out, false, 3, "timestamp", "%" PRIi64, sample->time);
+	output_json_key_format(out, true, 3, "pid", "%i", thread__pid(al.thread));
+	output_json_key_format(out, true, 3, "tid", "%i", thread__tid(al.thread));
+
+	if ((sample_type & PERF_SAMPLE_CPU))
+		output_json_key_format(out, true, 3, "cpu", "%i", sample->cpu);
+	else if (thread__cpu(al.thread) >= 0)
+		output_json_key_format(out, true, 3, "cpu", "%i", thread__cpu(al.thread));
+
+	output_json_key_string(out, true, 3, "comm", thread__comm_str(al.thread));
+
+	output_json_key_format(out, true, 3, "callchain", "[");
+	if (sample->callchain) {
+		unsigned int i;
+		bool ok;
+		bool first_callchain = true;
+
+		for (i = 0; i < sample->callchain->nr; ++i) {
+			u64 ip = sample->callchain->ips[i];
+			struct addr_location tal;
+
+			if (ip >= PERF_CONTEXT_MAX) {
+				switch (ip) {
+				case PERF_CONTEXT_HV:
+					cpumode = PERF_RECORD_MISC_HYPERVISOR;
+					break;
+				case PERF_CONTEXT_KERNEL:
+					cpumode = PERF_RECORD_MISC_KERNEL;
+					break;
+				case PERF_CONTEXT_USER:
+					cpumode = PERF_RECORD_MISC_USER;
+					break;
+				default:
+					pr_debug("invalid callchain context: %"
+							PRId64 "\n", (s64) ip);
+					break;
+				}
+				continue;
+			}
+
+			if (first_callchain)
+				first_callchain = false;
+			else
+				fputc(',', out);
+
+			addr_location__init(&tal);
+			ok = thread__find_symbol(al.thread, cpumode, ip, &tal);
+			output_sample_callchain_entry(tool, ip, ok ? &tal : NULL);
+			addr_location__exit(&tal);
+		}
+	} else {
+		output_sample_callchain_entry(tool, sample->ip, &al);
+	}
+	output_json_format(out, false, 3, "]");
+
+#ifdef HAVE_LIBTRACEEVENT
+	if (sample->raw_data) {
+		struct tep_event *tp_format = evsel__tp_format(sample->evsel);
+		struct tep_format_field **fields = tp_format ? tep_event_fields(tp_format) : NULL;
+
+		if (fields) {
+			int i = 0;
+
+			while (fields[i]) {
+				struct trace_seq s;
+
+				trace_seq_init(&s);
+				tep_print_field(&s, sample->raw_data, fields[i]);
+				output_json_key_string(out, true, 3, fields[i]->name, s.buffer);
+
+				i++;
+			}
+			free(fields);
+		}
+	}
+#endif
+	output_json_format(out, false, 2, "}");
+	addr_location__exit(&al);
+	return 0;
+}
+
+static void output_headers(struct perf_session *session, struct convert_json *c)
+{
+	struct stat st;
+	const struct perf_header *header = &session->header;
+	struct perf_env *env = perf_session__env(session);
+	int ret;
+	int fd = perf_data__fd(session->data);
+	int i;
+	FILE *out = c->out;
+
+	output_json_key_format(out, false, 2, "header-version", "%u", header->version);
+
+	ret = fstat(fd, &st);
+	if (ret >= 0) {
+		time_t stctime = st.st_mtime;
+		char buf[256];
+
+		strftime(buf, sizeof(buf), "%FT%TZ", gmtime(&stctime));
+		output_json_key_string(out, true, 2, "captured-on", buf);
+	} else {
+		pr_debug("Failed to get mtime of source file, not writing captured-on");
+	}
+
+	output_json_key_format(out, true, 2, "data-offset", "%" PRIu64, header->data_offset);
+	output_json_key_format(out, true, 2, "data-size", "%" PRIu64, header->data_size);
+	output_json_key_format(out, true, 2, "feat-offset", "%" PRIu64, header->feat_offset);
+
+	output_json_key_string(out, true, 2, "hostname", env->hostname);
+	output_json_key_string(out, true, 2, "os-release",
+			       perf_env__os_release(env));
+	output_json_key_string(out, true, 2, "arch", env->arch);
+
+	if (env->cpu_desc)
+		output_json_key_string(out, true, 2, "cpu-desc", env->cpu_desc);
+
+	output_json_key_string(out, true, 2, "cpuid", env->cpuid);
+	output_json_key_format(out, true, 2, "nrcpus-online", "%u", env->nr_cpus_online);
+	output_json_key_format(out, true, 2, "nrcpus-avail", "%u", env->nr_cpus_avail);
+
+	if (env->clock.enabled) {
+		output_json_key_format(out, true, 2, "clockid",
+				"%u", env->clock.clockid);
+		output_json_key_format(out, true, 2, "clock-time",
+				"%" PRIu64, env->clock.clockid_ns);
+		output_json_key_format(out, true, 2, "real-time",
+				"%" PRIu64, env->clock.tod_ns);
+	}
+
+	output_json_key_string(out, true, 2, "perf-version", env->version);
+
+	output_json_key_format(out, true, 2, "cmdline", "[");
+	for (i = 0; i < env->nr_cmdline; i++) {
+		output_json_delimiters(out, i != 0, 3);
+		output_json_string(c->out, env->cmdline_argv[i]);
+	}
+	output_json_format(out, false, 2, "]");
+}
+
+int bt_convert__perf2json(const char *_input_name, const char *output_name,
+		struct perf_data_convert_opts *opts __maybe_unused)
+{
+	struct perf_session *session;
+	int fd;
+	int ret = -1;
+	struct convert_json c = {
+		.first = true,
+		.events_count = 0,
+		.ptime_range = NULL,
+		.range_size = 0,
+		.range_num = 0,
+		.skipped = 0,
+	};
+	struct perf_data data = {
+		.mode = PERF_DATA_MODE_READ,
+		.path = _input_name,
+		.force = opts->force,
+	};
+
+	perf_tool__init(&c.tool, /*ordered_events=*/true);
+	c.tool.sample         = process_sample_event;
+	c.tool.mmap           = perf_event__process_mmap;
+	c.tool.mmap2          = perf_event__process_mmap2;
+	c.tool.comm           = perf_event__process_comm;
+	c.tool.namespaces     = perf_event__process_namespaces;
+	c.tool.cgroup         = perf_event__process_cgroup;
+	c.tool.exit           = perf_event__process_exit;
+	c.tool.fork           = perf_event__process_fork;
+	c.tool.lost           = perf_event__process_lost;
+#ifdef HAVE_LIBTRACEEVENT
+	c.tool.tracing_data   = perf_event__process_tracing_data;
+#endif
+	c.tool.build_id       = perf_event__process_build_id;
+	c.tool.id_index       = perf_event__process_id_index;
+	c.tool.auxtrace_info  = perf_event__process_auxtrace_info;
+	c.tool.auxtrace       = perf_event__process_auxtrace;
+	c.tool.event_update   = perf_event__process_event_update;
+	c.tool.attr           = perf_event__process_attr;
+	c.tool.feature        = perf_event__process_feature;
+	c.tool.ordering_requires_timestamps = true;
+
+	if (opts->all) {
+		pr_err("--all is currently unsupported for JSON output.\n");
+		goto err;
+	}
+	if (opts->tod) {
+		pr_err("--tod is currently unsupported for JSON output.\n");
+		goto err;
+	}
+
+	fd = open(output_name, O_CREAT | O_WRONLY | (opts->force ? O_TRUNC : O_EXCL), 0666);
+	if (fd == -1) {
+		if (errno == EEXIST)
+			pr_err("Output file exists. Use --force to overwrite it.\n");
+		else
+			pr_err("Error opening output file!\n");
+		goto err;
+	}
+
+	c.out = fdopen(fd, "w");
+	if (!c.out) {
+		fprintf(stderr, "Error opening output file!\n");
+		close(fd);
+		goto err;
+	}
+
+	session = perf_session__new(&data, &c.tool);
+	if (IS_ERR(session)) {
+		fprintf(stderr, "Error creating perf session!\n");
+		goto err_fclose;
+	}
+	if (symbol__init(perf_session__env(session)) < 0) {
+		fprintf(stderr, "Symbol init error!\n");
+		goto err_session_delete;
+	}
+
+	if (opts->time_str) {
+		ret = perf_time__parse_for_ranges(opts->time_str, session,
+						  &c.ptime_range,
+						  &c.range_size,
+						  &c.range_num);
+		if (ret < 0)
+			goto err_session_delete;
+	}
+
+	// The opening brace is printed manually because it isn't delimited from a
+	// previous value (i.e. we don't want a leading newline)
+	fputc('{', c.out);
+
+	// Version number for future-proofing. Most additions should be able to be
+	// done in a backwards-compatible way so this should only need to be bumped
+	// if some major breaking change must be made.
+	output_json_format(c.out, false, 1, "\"linux-perf-json-version\": 1");
+
+	// Output headers
+	output_json_format(c.out, true, 1, "\"headers\": {");
+	output_headers(session, &c);
+	output_json_format(c.out, false, 1, "}");
+
+	// Output samples
+	output_json_format(c.out, true, 1, "\"samples\": [");
+	perf_session__process_events(session);
+	output_json_format(c.out, false, 1, "]");
+	output_json_format(c.out, false, 0, "}");
+	fputc('\n', c.out);
+
+	fprintf(stderr,	"[ perf data convert: Converted '%s' into JSON data '%s' ]\n",
+		data.path, output_name);
+
+	fprintf(stderr,
+		"[ perf data convert: Converted and wrote %.3f MB (%" PRIu64 " samples) ]\n",
+		(ftell(c.out)) / 1024.0 / 1024.0, c.events_count);
+
+	if (c.skipped) {
+		fprintf(stderr,	"[ perf data convert: Skipped %" PRIu64 " samples ]\n",
+			c.skipped);
+	}
+
+	ret = 0;
+
+	if (c.ptime_range)
+		zfree(&c.ptime_range);
+
+err_session_delete:
+	perf_session__delete(session);
+err_fclose:
+	fclose(c.out);
+err:
+	return ret;
+}