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, 215 insertions, 0 deletions

diff --git a/tools/perf/tests/expand-cgroup.c b/tools/perf/tests/expand-cgroup.c
new file mode 100644
index 000000000..dd547f2f7
--- /dev/null
+++ b/tools/perf/tests/expand-cgroup.c
@@ -0,0 +1,215 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "tests.h"
+#include "debug.h"
+#include "evlist.h"
+#include "cgroup.h"
+#include "rblist.h"
+#include "metricgroup.h"
+#include "parse-events.h"
+#include "pmu-events/pmu-events.h"
+#include "pfm.h"
+#include "target.h"
+#include <subcmd/parse-options.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static int test_expand_events(struct evlist *evlist)
+{
+	int i, ret = TEST_FAIL;
+	int nr_events;
+	bool was_group_event;
+	int nr_members;  /* for the first evsel only */
+	const char cgrp_str[] = "A,B,C";
+	const char *cgrp_name[] = { "A", "B", "C" };
+	int nr_cgrps = ARRAY_SIZE(cgrp_name);
+	char **ev_name;
+	struct evsel *evsel;
+
+	TEST_ASSERT_VAL("evlist is empty", !evlist__empty(evlist));
+
+	nr_events = evlist->core.nr_entries;
+	ev_name = calloc(nr_events, sizeof(*ev_name));
+	if (ev_name == NULL) {
+		pr_debug("memory allocation failure\n");
+		return TEST_FAIL;
+	}
+	i = 0;
+	evlist__for_each_entry(evlist, evsel) {
+		ev_name[i] = strdup(evsel->name);
+		if (ev_name[i] == NULL) {
+			pr_debug("memory allocation failure\n");
+			goto out;
+		}
+		i++;
+	}
+	/* remember grouping info */
+	was_group_event = evsel__is_group_event(evlist__first(evlist));
+	nr_members = evlist__first(evlist)->core.nr_members;
+
+	ret = evlist__expand_cgroup(evlist, cgrp_str, false);
+	if (ret < 0) {
+		pr_debug("failed to expand events for cgroups\n");
+		goto out;
+	}
+
+	ret = TEST_FAIL;
+	if (evlist->core.nr_entries != nr_events * nr_cgrps) {
+		pr_debug("event count doesn't match\n");
+		goto out;
+	}
+
+	i = 0;
+	evlist__for_each_entry(evlist, evsel) {
+		if (!evsel__name_is(evsel, ev_name[i % nr_events])) {
+			pr_debug("event name doesn't match:\n");
+			pr_debug("  evsel[%d]: %s\n  expected: %s\n",
+				 i, evsel->name, ev_name[i % nr_events]);
+			goto out;
+		}
+		if (strcmp(evsel->cgrp->name, cgrp_name[i / nr_events])) {
+			pr_debug("cgroup name doesn't match:\n");
+			pr_debug("  evsel[%d]: %s\n  expected: %s\n",
+				 i, evsel->cgrp->name, cgrp_name[i / nr_events]);
+			goto out;
+		}
+
+		if ((i % nr_events) == 0) {
+			if (evsel__is_group_event(evsel) != was_group_event) {
+				pr_debug("event group doesn't match: got %s, expect %s\n",
+					 evsel__is_group_event(evsel) ? "true" : "false",
+					 was_group_event ? "true" : "false");
+				goto out;
+			}
+			if (evsel->core.nr_members != nr_members) {
+				pr_debug("event group member doesn't match: %d vs %d\n",
+					 evsel->core.nr_members, nr_members);
+				goto out;
+			}
+		}
+		i++;
+	}
+	ret = TEST_OK;
+
+out:	for (i = 0; i < nr_events; i++)
+		free(ev_name[i]);
+	free(ev_name);
+	return ret;
+}
+
+static int expand_default_events(void)
+{
+	int ret;
+	struct target target = {};
+	struct evlist *evlist = evlist__new_default(&target, /*sample_callchains=*/false);
+
+	TEST_ASSERT_VAL("failed to get evlist", evlist);
+
+	ret = test_expand_events(evlist);
+	evlist__delete(evlist);
+	return ret;
+}
+
+static int expand_group_events(void)
+{
+	int ret;
+	struct evlist *evlist;
+	struct parse_events_error err;
+	const char event_str[] = "{cycles,instructions}";
+
+	symbol_conf.event_group = true;
+
+	evlist = evlist__new();
+	TEST_ASSERT_VAL("failed to get evlist", evlist);
+
+	parse_events_error__init(&err);
+	ret = parse_events(evlist, event_str, &err);
+	if (ret < 0) {
+		pr_debug("failed to parse event '%s', err %d\n", event_str, ret);
+		parse_events_error__print(&err, event_str);
+		goto out;
+	}
+
+	ret = test_expand_events(evlist);
+out:
+	parse_events_error__exit(&err);
+	evlist__delete(evlist);
+	return ret;
+}
+
+static int expand_libpfm_events(void)
+{
+	int ret;
+	struct evlist *evlist;
+	const char event_str[] = "CYCLES";
+	struct option opt = {
+		.value = &evlist,
+	};
+
+	symbol_conf.event_group = true;
+
+	evlist = evlist__new();
+	TEST_ASSERT_VAL("failed to get evlist", evlist);
+
+	ret = parse_libpfm_events_option(&opt, event_str, 0);
+	if (ret < 0) {
+		pr_debug("failed to parse libpfm event '%s', err %d\n",
+			 event_str, ret);
+		goto out;
+	}
+	if (evlist__empty(evlist)) {
+		pr_debug("libpfm was not enabled\n");
+		goto out;
+	}
+
+	ret = test_expand_events(evlist);
+out:
+	evlist__delete(evlist);
+	return ret;
+}
+
+static int expand_metric_events(void)
+{
+	int ret;
+	struct evlist *evlist;
+	const char metric_str[] = "CPI";
+	const struct pmu_metrics_table *pme_test;
+
+	evlist = evlist__new();
+	TEST_ASSERT_VAL("failed to get evlist", evlist);
+
+	pme_test = find_core_metrics_table("testarch", "testcpu");
+	ret = metricgroup__parse_groups_test(evlist, pme_test, metric_str);
+	if (ret < 0) {
+		pr_debug("failed to parse '%s' metric\n", metric_str);
+		goto out;
+	}
+
+	ret = test_expand_events(evlist);
+
+out:
+	evlist__delete(evlist);
+	return ret;
+}
+
+static int test__expand_cgroup_events(struct test_suite *test __maybe_unused,
+				      int subtest __maybe_unused)
+{
+	int ret;
+
+	ret = expand_default_events();
+	TEST_ASSERT_EQUAL("failed to expand default events", ret, 0);
+
+	ret = expand_group_events();
+	TEST_ASSERT_EQUAL("failed to expand event group", ret, 0);
+
+	ret = expand_libpfm_events();
+	TEST_ASSERT_EQUAL("failed to expand event group", ret, 0);
+
+	ret = expand_metric_events();
+	TEST_ASSERT_EQUAL("failed to expand metric events", ret, 0);
+
+	return ret;
+}
+
+DEFINE_SUITE("Event expansion for cgroups", expand_cgroup_events);