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, 465 insertions, 0 deletions

diff --git a/tools/perf/util/bpf-trace-summary.c b/tools/perf/util/bpf-trace-summary.c
new file mode 100644
index 000000000..9a31dbf06
--- /dev/null
+++ b/tools/perf/util/bpf-trace-summary.c
@@ -0,0 +1,465 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <errno.h>
+#include <inttypes.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "dwarf-regs.h" /* for EM_HOST */
+#include "trace/beauty/syscalltbl.h"
+#include "util/cgroup.h"
+#include "util/hashmap.h"
+#include "util/trace.h"
+#include "util/util.h"
+#include <bpf/bpf.h>
+#include <linux/rbtree.h>
+#include <linux/time64.h>
+#include <tools/libc_compat.h> /* reallocarray */
+
+#include "bpf_skel/syscall_summary.h"
+#include "bpf_skel/syscall_summary.skel.h"
+
+
+static struct syscall_summary_bpf *skel;
+static struct rb_root cgroups = RB_ROOT;
+
+int trace_prepare_bpf_summary(enum trace_summary_mode mode)
+{
+	skel = syscall_summary_bpf__open();
+	if (skel == NULL) {
+		fprintf(stderr, "failed to open syscall summary bpf skeleton\n");
+		return -1;
+	}
+
+	if (mode == SUMMARY__BY_THREAD)
+		skel->rodata->aggr_mode = SYSCALL_AGGR_THREAD;
+	else if (mode == SUMMARY__BY_CGROUP)
+		skel->rodata->aggr_mode = SYSCALL_AGGR_CGROUP;
+	else
+		skel->rodata->aggr_mode = SYSCALL_AGGR_CPU;
+
+	if (cgroup_is_v2("perf_event") > 0)
+		skel->rodata->use_cgroup_v2 = 1;
+
+	if (syscall_summary_bpf__load(skel) < 0) {
+		fprintf(stderr, "failed to load syscall summary bpf skeleton\n");
+		return -1;
+	}
+
+	if (syscall_summary_bpf__attach(skel) < 0) {
+		fprintf(stderr, "failed to attach syscall summary bpf skeleton\n");
+		return -1;
+	}
+
+	if (mode == SUMMARY__BY_CGROUP)
+		read_all_cgroups(&cgroups);
+
+	return 0;
+}
+
+void trace_start_bpf_summary(void)
+{
+	skel->bss->enabled = 1;
+}
+
+void trace_end_bpf_summary(void)
+{
+	skel->bss->enabled = 0;
+}
+
+struct syscall_node {
+	int syscall_nr;
+	struct syscall_stats stats;
+};
+
+static double rel_stddev(struct syscall_stats *stat)
+{
+	double variance, average;
+
+	if (stat->count < 2)
+		return 0;
+
+	average = (double)stat->total_time / stat->count;
+
+	variance = stat->squared_sum;
+	variance -= (stat->total_time * stat->total_time) / stat->count;
+	variance /= stat->count - 1;
+
+	return 100 * sqrt(variance / stat->count) / average;
+}
+
+/*
+ * The syscall_data is to maintain syscall stats ordered by total time.
+ * It supports different summary modes like per-thread or global.
+ *
+ * For per-thread stats, it uses two-level data strurcture -
+ * syscall_data is keyed by TID and has an array of nodes which
+ * represents each syscall for the thread.
+ *
+ * For global stats, it's still two-level technically but we don't need
+ * per-cpu analysis so it's keyed by the syscall number to combine stats
+ * from different CPUs.  And syscall_data always has a syscall_node so
+ * it can effectively work as flat hierarchy.
+ *
+ * For per-cgroup stats, it uses two-level data structure like thread
+ * syscall_data is keyed by CGROUP and has an array of node which
+ * represents each syscall for the cgroup.
+ */
+struct syscall_data {
+	u64 key; /* tid if AGGR_THREAD, syscall-nr if AGGR_CPU, cgroup if AGGR_CGROUP */
+	int nr_events;
+	int nr_nodes;
+	u64 total_time;
+	struct syscall_node *nodes;
+};
+
+static int datacmp(const void *a, const void *b)
+{
+	const struct syscall_data * const *sa = a;
+	const struct syscall_data * const *sb = b;
+
+	return (*sa)->total_time > (*sb)->total_time ? -1 : 1;
+}
+
+static int nodecmp(const void *a, const void *b)
+{
+	const struct syscall_node *na = a;
+	const struct syscall_node *nb = b;
+
+	return na->stats.total_time > nb->stats.total_time ? -1 : 1;
+}
+
+static size_t sc_node_hash(long key, void *ctx __maybe_unused)
+{
+	return key;
+}
+
+static bool sc_node_equal(long key1, long key2, void *ctx __maybe_unused)
+{
+	return key1 == key2;
+}
+
+static int print_common_stats(struct syscall_data *data, int max_summary, FILE *fp)
+{
+	int printed = 0;
+
+	if (max_summary == 0 || max_summary > data->nr_nodes)
+		max_summary = data->nr_nodes;
+
+	for (int i = 0; i < max_summary; i++) {
+		struct syscall_node *node = &data->nodes[i];
+		struct syscall_stats *stat = &node->stats;
+		double total = (double)(stat->total_time) / NSEC_PER_MSEC;
+		double min = (double)(stat->min_time) / NSEC_PER_MSEC;
+		double max = (double)(stat->max_time) / NSEC_PER_MSEC;
+		double avg = total / stat->count;
+		const char *name;
+
+		/* TODO: support other ABIs */
+		name = syscalltbl__name(EM_HOST, node->syscall_nr);
+		if (name)
+			printed += fprintf(fp, "   %-15s", name);
+		else
+			printed += fprintf(fp, "   syscall:%-7d", node->syscall_nr);
+
+		printed += fprintf(fp, " %8u %6u %9.3f %9.3f %9.3f %9.3f %9.2f%%\n",
+				   stat->count, stat->error, total, min, avg, max,
+				   rel_stddev(stat));
+	}
+	return printed;
+}
+
+static int update_thread_stats(struct hashmap *hash, struct syscall_key *map_key,
+			       struct syscall_stats *map_data)
+{
+	struct syscall_data *data;
+	struct syscall_node *nodes;
+
+	if (!hashmap__find(hash, map_key->cpu_or_tid, &data)) {
+		data = zalloc(sizeof(*data));
+		if (data == NULL)
+			return -ENOMEM;
+
+		data->key = map_key->cpu_or_tid;
+		if (hashmap__add(hash, data->key, data) < 0) {
+			free(data);
+			return -ENOMEM;
+		}
+	}
+
+	/* update thread total stats */
+	data->nr_events += map_data->count;
+	data->total_time += map_data->total_time;
+
+	nodes = reallocarray(data->nodes, data->nr_nodes + 1, sizeof(*nodes));
+	if (nodes == NULL)
+		return -ENOMEM;
+
+	data->nodes = nodes;
+	nodes = &data->nodes[data->nr_nodes++];
+	nodes->syscall_nr = map_key->nr;
+
+	/* each thread has an entry for each syscall, just use the stat */
+	memcpy(&nodes->stats, map_data, sizeof(*map_data));
+	return 0;
+}
+
+static int print_thread_stat(struct syscall_data *data, int max_summary, FILE *fp)
+{
+	int printed = 0;
+
+	qsort(data->nodes, data->nr_nodes, sizeof(*data->nodes), nodecmp);
+
+	printed += fprintf(fp, " thread (%d), ", (int)data->key);
+	printed += fprintf(fp, "%d events\n\n", data->nr_events);
+
+	printed += fprintf(fp, "   syscall            calls  errors  total       min       avg       max       stddev\n");
+	printed += fprintf(fp, "                                     (msec)    (msec)    (msec)    (msec)        (%%)\n");
+	printed += fprintf(fp, "   --------------- --------  ------ -------- --------- --------- ---------     ------\n");
+
+	printed += print_common_stats(data, max_summary, fp);
+	printed += fprintf(fp, "\n\n");
+
+	return printed;
+}
+
+static int print_thread_stats(struct syscall_data **data, int nr_data, int max_summary, FILE *fp)
+{
+	int printed = 0;
+
+	for (int i = 0; i < nr_data; i++)
+		printed += print_thread_stat(data[i], max_summary, fp);
+
+	return printed;
+}
+
+static int update_total_stats(struct hashmap *hash, struct syscall_key *map_key,
+			      struct syscall_stats *map_data)
+{
+	struct syscall_data *data;
+	struct syscall_stats *stat;
+
+	if (!hashmap__find(hash, map_key->nr, &data)) {
+		data = zalloc(sizeof(*data));
+		if (data == NULL)
+			return -ENOMEM;
+
+		data->nodes = zalloc(sizeof(*data->nodes));
+		if (data->nodes == NULL) {
+			free(data);
+			return -ENOMEM;
+		}
+
+		data->nr_nodes = 1;
+		data->key = map_key->nr;
+		data->nodes->syscall_nr = data->key;
+
+		if (hashmap__add(hash, data->key, data) < 0) {
+			free(data->nodes);
+			free(data);
+			return -ENOMEM;
+		}
+	}
+
+	/* update total stats for this syscall */
+	data->nr_events += map_data->count;
+	data->total_time += map_data->total_time;
+
+	/* This is sum of the same syscall from different CPUs */
+	stat = &data->nodes->stats;
+
+	stat->total_time += map_data->total_time;
+	stat->squared_sum += map_data->squared_sum;
+	stat->count += map_data->count;
+	stat->error += map_data->error;
+
+	if (stat->max_time < map_data->max_time)
+		stat->max_time = map_data->max_time;
+	if (stat->min_time > map_data->min_time || stat->min_time == 0)
+		stat->min_time = map_data->min_time;
+
+	return 0;
+}
+
+static int print_total_stats(struct syscall_data **data, int nr_data, int max_summary, FILE *fp)
+{
+	int printed = 0;
+	int nr_events = 0;
+
+	for (int i = 0; i < nr_data; i++)
+		nr_events += data[i]->nr_events;
+
+	printed += fprintf(fp, " total, %d events\n\n", nr_events);
+
+	printed += fprintf(fp, "   syscall            calls  errors  total       min       avg       max       stddev\n");
+	printed += fprintf(fp, "                                     (msec)    (msec)    (msec)    (msec)        (%%)\n");
+	printed += fprintf(fp, "   --------------- --------  ------ -------- --------- --------- ---------     ------\n");
+
+	if (max_summary == 0 || max_summary > nr_data)
+		max_summary = nr_data;
+
+	for (int i = 0; i < max_summary; i++)
+		printed += print_common_stats(data[i], max_summary, fp);
+
+	printed += fprintf(fp, "\n\n");
+	return printed;
+}
+
+static int update_cgroup_stats(struct hashmap *hash, struct syscall_key *map_key,
+			       struct syscall_stats *map_data)
+{
+	struct syscall_data *data;
+	struct syscall_node *nodes;
+
+	if (!hashmap__find(hash, map_key->cgroup, &data)) {
+		data = zalloc(sizeof(*data));
+		if (data == NULL)
+			return -ENOMEM;
+
+		data->key = map_key->cgroup;
+		if (hashmap__add(hash, data->key, data) < 0) {
+			free(data);
+			return -ENOMEM;
+		}
+	}
+
+	/* update thread total stats */
+	data->nr_events += map_data->count;
+	data->total_time += map_data->total_time;
+
+	nodes = reallocarray(data->nodes, data->nr_nodes + 1, sizeof(*nodes));
+	if (nodes == NULL)
+		return -ENOMEM;
+
+	data->nodes = nodes;
+	nodes = &data->nodes[data->nr_nodes++];
+	nodes->syscall_nr = map_key->nr;
+
+	/* each thread has an entry for each syscall, just use the stat */
+	memcpy(&nodes->stats, map_data, sizeof(*map_data));
+	return 0;
+}
+
+static int print_cgroup_stat(struct syscall_data *data, int max_summary, FILE *fp)
+{
+	int printed = 0;
+	struct cgroup *cgrp = __cgroup__find(&cgroups, data->key);
+
+	qsort(data->nodes, data->nr_nodes, sizeof(*data->nodes), nodecmp);
+
+	if (cgrp)
+		printed += fprintf(fp, " cgroup %s,", cgrp->name);
+	else
+		printed += fprintf(fp, " cgroup id:%lu,", (unsigned long)data->key);
+
+	printed += fprintf(fp, " %d events\n\n", data->nr_events);
+
+	printed += fprintf(fp, "   syscall            calls  errors  total       min       avg       max       stddev\n");
+	printed += fprintf(fp, "                                     (msec)    (msec)    (msec)    (msec)        (%%)\n");
+	printed += fprintf(fp, "   --------------- --------  ------ -------- --------- --------- ---------     ------\n");
+
+	printed += print_common_stats(data, max_summary, fp);
+	printed += fprintf(fp, "\n\n");
+
+	return printed;
+}
+
+static int print_cgroup_stats(struct syscall_data **data, int nr_data, int max_summary, FILE *fp)
+{
+	int printed = 0;
+
+	for (int i = 0; i < nr_data; i++)
+		printed += print_cgroup_stat(data[i], max_summary, fp);
+
+	return printed;
+}
+
+int trace_print_bpf_summary(FILE *fp, int max_summary)
+{
+	struct bpf_map *map = skel->maps.syscall_stats_map;
+	struct syscall_key *prev_key, key;
+	struct syscall_data **data = NULL;
+	struct hashmap schash;
+	struct hashmap_entry *entry;
+	int nr_data = 0;
+	int printed = 0;
+	int i;
+	size_t bkt;
+
+	hashmap__init(&schash, sc_node_hash, sc_node_equal, /*ctx=*/NULL);
+
+	printed = fprintf(fp, "\n Summary of events:\n\n");
+
+	/* get stats from the bpf map */
+	prev_key = NULL;
+	while (!bpf_map__get_next_key(map, prev_key, &key, sizeof(key))) {
+		struct syscall_stats stat;
+
+		if (!bpf_map__lookup_elem(map, &key, sizeof(key), &stat, sizeof(stat), 0)) {
+			switch (skel->rodata->aggr_mode) {
+			case SYSCALL_AGGR_THREAD:
+				update_thread_stats(&schash, &key, &stat);
+				break;
+			case SYSCALL_AGGR_CPU:
+				update_total_stats(&schash, &key, &stat);
+				break;
+			case SYSCALL_AGGR_CGROUP:
+				update_cgroup_stats(&schash, &key, &stat);
+				break;
+			default:
+				break;
+			}
+		}
+
+		prev_key = &key;
+	}
+
+	nr_data = hashmap__size(&schash);
+	data = calloc(nr_data, sizeof(*data));
+	if (data == NULL)
+		goto out;
+
+	i = 0;
+	hashmap__for_each_entry(&schash, entry, bkt)
+		data[i++] = entry->pvalue;
+
+	qsort(data, nr_data, sizeof(*data), datacmp);
+
+	switch (skel->rodata->aggr_mode) {
+	case SYSCALL_AGGR_THREAD:
+		printed += print_thread_stats(data, nr_data, max_summary, fp);
+		break;
+	case SYSCALL_AGGR_CPU:
+		printed += print_total_stats(data, nr_data, max_summary, fp);
+		break;
+	case SYSCALL_AGGR_CGROUP:
+		printed += print_cgroup_stats(data, nr_data, max_summary, fp);
+		break;
+	default:
+		break;
+	}
+
+	for (i = 0; i < nr_data && data; i++) {
+		free(data[i]->nodes);
+		free(data[i]);
+	}
+	free(data);
+
+out:
+	hashmap__clear(&schash);
+	return printed;
+}
+
+void trace_cleanup_bpf_summary(void)
+{
+	if (!RB_EMPTY_ROOT(&cgroups)) {
+		struct cgroup *cgrp, *tmp;
+
+		rbtree_postorder_for_each_entry_safe(cgrp, tmp, &cgroups, node)
+			cgroup__put(cgrp);
+
+		cgroups = RB_ROOT;
+	}
+
+	syscall_summary_bpf__destroy(skel);
+}