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, 321 insertions, 0 deletions

diff --git a/tools/perf/util/pfm.c b/tools/perf/util/pfm.c
new file mode 100644
index 000000000..d9043f4af
--- /dev/null
+++ b/tools/perf/util/pfm.c
@@ -0,0 +1,321 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Support for libpfm4 event encoding.
+ *
+ * Copyright 2020 Google LLC.
+ */
+#include "util/cpumap.h"
+#include "util/debug.h"
+#include "util/event.h"
+#include "util/evlist.h"
+#include "util/evsel.h"
+#include "util/parse-events.h"
+#include "util/pmus.h"
+#include "util/pfm.h"
+#include "util/strbuf.h"
+#include "util/thread_map.h"
+
+#include <errno.h>
+#include <string.h>
+#include <linux/kernel.h>
+#include <perfmon/pfmlib_perf_event.h>
+
+static void libpfm_initialize(void)
+{
+	int ret;
+
+	ret = pfm_initialize();
+	if (ret != PFM_SUCCESS) {
+		ui__warning("libpfm failed to initialize: %s\n",
+			pfm_strerror(ret));
+	}
+}
+
+int parse_libpfm_events_option(const struct option *opt, const char *str,
+			int unset __maybe_unused)
+{
+	struct evlist *evlist = *(struct evlist **)opt->value;
+	struct perf_event_attr attr;
+	struct perf_pmu *pmu;
+	struct evsel *evsel, *grp_leader = NULL;
+	char *p, *q, *p_orig;
+	const char *sep;
+	int grp_evt = -1;
+	int ret;
+
+	libpfm_initialize();
+
+	p_orig = p = strdup(str);
+	if (!p)
+		return -1;
+
+	for (q = p; strsep(&p, ",{}"); q = p) {
+		sep = p ? str + (p - p_orig - 1) : "";
+		if (*sep == '{') {
+			if (grp_evt > -1) {
+				ui__error(
+					"nested event groups not supported\n");
+				goto error;
+			}
+			grp_evt++;
+		}
+
+		/* no event */
+		if (*q == '\0') {
+			if (*sep == '}') {
+				if (grp_evt < 0) {
+					ui__error("cannot close a non-existing event group\n");
+					goto error;
+				}
+				grp_evt--;
+			}
+			continue;
+		}
+
+		memset(&attr, 0, sizeof(attr));
+		event_attr_init(&attr);
+
+		ret = pfm_get_perf_event_encoding(q, PFM_PLM0|PFM_PLM3,
+						&attr, NULL, NULL);
+
+		if (ret != PFM_SUCCESS) {
+			ui__error("failed to parse event %s : %s\n", str,
+				  pfm_strerror(ret));
+			goto error;
+		}
+
+		pmu = perf_pmus__find_by_type((unsigned int)attr.type);
+		evsel = parse_events__add_event(evlist->core.nr_entries,
+						&attr, q, /*metric_id=*/NULL,
+						pmu);
+		if (evsel == NULL)
+			goto error;
+
+		evsel->is_libpfm_event = true;
+
+		evlist__add(evlist, evsel);
+
+		if (grp_evt == 0)
+			grp_leader = evsel;
+
+		if (grp_evt > -1) {
+			evsel__set_leader(evsel, grp_leader);
+			grp_leader->core.nr_members++;
+			grp_evt++;
+		}
+
+		if (*sep == '}') {
+			if (grp_evt < 0) {
+				ui__error(
+				   "cannot close a non-existing event group\n");
+				goto error;
+			}
+			grp_leader = NULL;
+			grp_evt = -1;
+		}
+	}
+	free(p_orig);
+	return 0;
+error:
+	free(p_orig);
+	return -1;
+}
+
+static bool is_libpfm_event_supported(const char *name, struct perf_cpu_map *cpus,
+				      struct perf_thread_map *threads)
+{
+	struct perf_pmu *pmu;
+	struct evsel *evsel;
+	struct perf_event_attr attr = {};
+	bool result = true;
+	int ret;
+
+	ret = pfm_get_perf_event_encoding(name, PFM_PLM0|PFM_PLM3,
+					  &attr, NULL, NULL);
+	if (ret != PFM_SUCCESS)
+		return false;
+
+	pmu = perf_pmus__find_by_type((unsigned int)attr.type);
+	evsel = parse_events__add_event(0, &attr, name, /*metric_id=*/NULL, pmu);
+	if (evsel == NULL)
+		return false;
+
+	evsel->is_libpfm_event = true;
+
+	ret = evsel__open(evsel, cpus, threads);
+	if (ret == -EACCES) {
+		/*
+		 * This happens if the paranoid value
+		 * /proc/sys/kernel/perf_event_paranoid is set to 2
+		 * Re-run with exclude_kernel set; we don't do that
+		 * by default as some ARM machines do not support it.
+		 *
+		 */
+		evsel->core.attr.exclude_kernel = 1;
+		ret = evsel__open(evsel, cpus, threads);
+
+	}
+	if (ret < 0)
+		result = false;
+
+	evsel__close(evsel);
+	evsel__delete(evsel);
+
+	return result;
+}
+
+static const char *srcs[PFM_ATTR_CTRL_MAX] = {
+	[PFM_ATTR_CTRL_UNKNOWN] = "???",
+	[PFM_ATTR_CTRL_PMU] = "PMU",
+	[PFM_ATTR_CTRL_PERF_EVENT] = "perf_event",
+};
+
+static void
+print_attr_flags(struct strbuf *buf, const pfm_event_attr_info_t *info)
+{
+	if (info->is_dfl)
+		strbuf_addf(buf, "[default] ");
+
+	if (info->is_precise)
+		strbuf_addf(buf, "[precise] ");
+}
+
+static void
+print_libpfm_event(const struct print_callbacks *print_cb, void *print_state,
+		const pfm_pmu_info_t *pinfo, const pfm_event_info_t *info,
+		struct strbuf *buf)
+{
+	int j, ret;
+	char topic[80], name[80];
+	struct perf_cpu_map *cpus = perf_cpu_map__empty_new(1);
+	struct perf_thread_map *threads = thread_map__new_by_tid(0);
+
+	strbuf_setlen(buf, 0);
+	snprintf(topic, sizeof(topic), "pfm %s", pinfo->name);
+
+	snprintf(name, sizeof(name), "%s::%s", pinfo->name, info->name);
+	strbuf_addf(buf, "Code: 0x%"PRIx64"\n", info->code);
+
+	pfm_for_each_event_attr(j, info) {
+		pfm_event_attr_info_t ainfo;
+		const char *src;
+
+		ainfo.size = sizeof(ainfo);
+		ret = pfm_get_event_attr_info(info->idx, j, PFM_OS_PERF_EVENT_EXT, &ainfo);
+		if (ret != PFM_SUCCESS)
+			continue;
+
+		if (ainfo.ctrl >= PFM_ATTR_CTRL_MAX)
+			ainfo.ctrl = PFM_ATTR_CTRL_UNKNOWN;
+
+		src = srcs[ainfo.ctrl];
+		switch (ainfo.type) {
+		case PFM_ATTR_UMASK: /* Ignore for now */
+			break;
+		case PFM_ATTR_MOD_BOOL:
+			strbuf_addf(buf, " Modif: %s: [%s] : %s (boolean)\n", src,
+				    ainfo.name, ainfo.desc);
+			break;
+		case PFM_ATTR_MOD_INTEGER:
+			strbuf_addf(buf, " Modif: %s: [%s] : %s (integer)\n", src,
+				    ainfo.name, ainfo.desc);
+			break;
+		case PFM_ATTR_NONE:
+		case PFM_ATTR_RAW_UMASK:
+		case PFM_ATTR_MAX:
+		default:
+			strbuf_addf(buf, " Attr: %s: [%s] : %s\n", src,
+				    ainfo.name, ainfo.desc);
+		}
+	}
+
+	if (is_libpfm_event_supported(name, cpus, threads)) {
+		print_cb->print_event(print_state, topic, pinfo->name,
+				      /*pmu_type=*/PERF_TYPE_RAW,
+				      name, info->equiv,
+				      /*scale_unit=*/NULL,
+				      /*deprecated=*/NULL, "PFM event",
+				      info->desc, /*long_desc=*/NULL,
+				      /*encoding_desc=*/buf->buf);
+	}
+
+	pfm_for_each_event_attr(j, info) {
+		pfm_event_attr_info_t ainfo;
+		const char *src;
+
+		strbuf_setlen(buf, 0);
+
+		ainfo.size = sizeof(ainfo);
+		ret = pfm_get_event_attr_info(info->idx, j, PFM_OS_PERF_EVENT_EXT, &ainfo);
+		if (ret != PFM_SUCCESS)
+			continue;
+
+		if (ainfo.ctrl >= PFM_ATTR_CTRL_MAX)
+			ainfo.ctrl = PFM_ATTR_CTRL_UNKNOWN;
+
+		src = srcs[ainfo.ctrl];
+		if (ainfo.type == PFM_ATTR_UMASK) {
+			strbuf_addf(buf, "Umask: 0x%02"PRIx64" : %s: ",
+				ainfo.code, src);
+			print_attr_flags(buf, &ainfo);
+			snprintf(name, sizeof(name), "%s::%s:%s",
+				 pinfo->name, info->name, ainfo.name);
+
+			if (!is_libpfm_event_supported(name, cpus, threads))
+				continue;
+
+			print_cb->print_event(print_state,
+					topic,
+					pinfo->name,
+					/*pmu_type=*/PERF_TYPE_RAW,
+					name, /*alias=*/NULL,
+					/*scale_unit=*/NULL,
+					/*deprecated=*/NULL, "PFM event",
+					ainfo.desc, /*long_desc=*/NULL,
+					/*encoding_desc=*/buf->buf);
+		}
+	}
+
+	perf_cpu_map__put(cpus);
+	perf_thread_map__put(threads);
+}
+
+void print_libpfm_events(const struct print_callbacks *print_cb, void *print_state)
+{
+	pfm_event_info_t info;
+	pfm_pmu_info_t pinfo;
+	int p, ret;
+	struct strbuf storage;
+
+	libpfm_initialize();
+
+	/* initialize to zero to indicate ABI version */
+	info.size  = sizeof(info);
+	pinfo.size = sizeof(pinfo);
+
+	strbuf_init(&storage, 2048);
+
+	pfm_for_all_pmus(p) {
+		ret = pfm_get_pmu_info(p, &pinfo);
+		if (ret != PFM_SUCCESS)
+			continue;
+
+		/* only print events that are supported by host HW */
+		if (!pinfo.is_present)
+			continue;
+
+		/* handled by perf directly */
+		if (pinfo.pmu == PFM_PMU_PERF_EVENT)
+			continue;
+
+		for (int i = pinfo.first_event; i != -1; i = pfm_get_event_next(i)) {
+			ret = pfm_get_event_info(i, PFM_OS_PERF_EVENT_EXT,
+						&info);
+			if (ret != PFM_SUCCESS)
+				continue;
+
+			print_libpfm_event(print_cb, print_state, &pinfo, &info, &storage);
+		}
+	}
+	strbuf_release(&storage);
+}