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, 558 insertions, 0 deletions

diff --git a/tools/perf/builtin-buildid-cache.c b/tools/perf/builtin-buildid-cache.c
new file mode 100644
index 000000000..539e779e3
--- /dev/null
+++ b/tools/perf/builtin-buildid-cache.c
@@ -0,0 +1,558 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * builtin-buildid-cache.c
+ *
+ * Builtin buildid-cache command: Manages build-id cache
+ *
+ * Copyright (C) 2010, Red Hat Inc.
+ * Copyright (C) 2010, Arnaldo Carvalho de Melo <acme@redhat.com>
+ */
+#include <sys/types.h>
+#include <sys/time.h>
+#include <time.h>
+#include <dirent.h>
+#include <errno.h>
+#include <unistd.h>
+#include "builtin.h"
+#include "namespaces.h"
+#include "util/debug.h"
+#include "util/header.h"
+#include <subcmd/pager.h>
+#include <subcmd/parse-options.h>
+#include "util/strlist.h"
+#include "util/build-id.h"
+#include "util/session.h"
+#include "util/dso.h"
+#include "util/symbol.h"
+#include "util/time-utils.h"
+#include "util/util.h"
+#include "util/probe-file.h"
+#include "util/config.h"
+#include <linux/string.h>
+#include <linux/err.h>
+
+static int build_id_cache__kcore_buildid(const char *proc_dir, char *sbuildid, size_t sbuildid_size)
+{
+	char root_dir[PATH_MAX];
+	char *p;
+
+	strlcpy(root_dir, proc_dir, sizeof(root_dir));
+
+	p = strrchr(root_dir, '/');
+	if (!p)
+		return -1;
+	*p = '\0';
+	return sysfs__snprintf_build_id(root_dir, sbuildid, sbuildid_size);
+}
+
+static int build_id_cache__kcore_dir(char *dir, size_t sz)
+{
+	return fetch_current_timestamp(dir, sz);
+}
+
+static bool same_kallsyms_reloc(const char *from_dir, char *to_dir)
+{
+	char from[PATH_MAX];
+	char to[PATH_MAX];
+	const char *name;
+	u64 addr1 = 0, addr2 = 0;
+	int i, err = -1;
+
+	scnprintf(from, sizeof(from), "%s/kallsyms", from_dir);
+	scnprintf(to, sizeof(to), "%s/kallsyms", to_dir);
+
+	for (i = 0; (name = ref_reloc_sym_names[i]) != NULL; i++) {
+		err = kallsyms__get_function_start(from, name, &addr1);
+		if (!err)
+			break;
+	}
+
+	if (err)
+		return false;
+
+	if (kallsyms__get_function_start(to, name, &addr2))
+		return false;
+
+	return addr1 == addr2;
+}
+
+static int build_id_cache__kcore_existing(const char *from_dir, char *to_dir,
+					  size_t to_dir_sz)
+{
+	char from[PATH_MAX];
+	char to[PATH_MAX];
+	char to_subdir[PATH_MAX];
+	struct dirent *dent;
+	int ret = -1;
+	DIR *d;
+
+	d = opendir(to_dir);
+	if (!d)
+		return -1;
+
+	scnprintf(from, sizeof(from), "%s/modules", from_dir);
+
+	while (1) {
+		dent = readdir(d);
+		if (!dent)
+			break;
+		if (dent->d_type != DT_DIR)
+			continue;
+		scnprintf(to, sizeof(to), "%s/%s/modules", to_dir,
+			  dent->d_name);
+		scnprintf(to_subdir, sizeof(to_subdir), "%s/%s",
+			  to_dir, dent->d_name);
+		if (!compare_proc_modules(from, to) &&
+		    same_kallsyms_reloc(from_dir, to_subdir)) {
+			strlcpy(to_dir, to_subdir, to_dir_sz);
+			ret = 0;
+			break;
+		}
+	}
+
+	closedir(d);
+
+	return ret;
+}
+
+static int build_id_cache__add_kcore(const char *filename, bool force)
+{
+	char dir[32], sbuildid[SBUILD_ID_SIZE];
+	char from_dir[PATH_MAX], to_dir[PATH_MAX];
+	char *p;
+
+	strlcpy(from_dir, filename, sizeof(from_dir));
+
+	p = strrchr(from_dir, '/');
+	if (!p || strcmp(p + 1, "kcore"))
+		return -1;
+	*p = '\0';
+
+	if (build_id_cache__kcore_buildid(from_dir, sbuildid, sizeof(sbuildid)) < 0)
+		return -1;
+
+	scnprintf(to_dir, sizeof(to_dir), "%s/%s/%s",
+		  buildid_dir, DSO__NAME_KCORE, sbuildid);
+
+	if (!force &&
+	    !build_id_cache__kcore_existing(from_dir, to_dir, sizeof(to_dir))) {
+		pr_debug("same kcore found in %s\n", to_dir);
+		return 0;
+	}
+
+	if (build_id_cache__kcore_dir(dir, sizeof(dir)))
+		return -1;
+
+	scnprintf(to_dir, sizeof(to_dir), "%s/%s/%s/%s",
+		  buildid_dir, DSO__NAME_KCORE, sbuildid, dir);
+
+	if (mkdir_p(to_dir, 0755))
+		return -1;
+
+	if (kcore_copy(from_dir, to_dir)) {
+		/* Remove YYYYmmddHHMMSShh directory */
+		if (!rmdir(to_dir)) {
+			p = strrchr(to_dir, '/');
+			if (p)
+				*p = '\0';
+			/* Try to remove buildid directory */
+			if (!rmdir(to_dir)) {
+				p = strrchr(to_dir, '/');
+				if (p)
+					*p = '\0';
+				/* Try to remove [kernel.kcore] directory */
+				rmdir(to_dir);
+			}
+		}
+		return -1;
+	}
+
+	pr_debug("kcore added to build-id cache directory %s\n", to_dir);
+
+	return 0;
+}
+
+static int build_id_cache__add_file(const char *filename, struct nsinfo *nsi)
+{
+	char sbuild_id[SBUILD_ID_SIZE];
+	struct build_id bid = { .size = 0, };
+	int err;
+	struct nscookie nsc;
+
+	nsinfo__mountns_enter(nsi, &nsc);
+	err = filename__read_build_id(filename, &bid);
+	nsinfo__mountns_exit(&nsc);
+	if (err < 0) {
+		pr_debug("Couldn't read a build-id in %s\n", filename);
+		return -1;
+	}
+
+	build_id__snprintf(&bid, sbuild_id, sizeof(sbuild_id));
+	err = build_id_cache__add_s(sbuild_id, filename, nsi,
+				    false, false);
+	pr_debug("Adding %s %s: %s\n", sbuild_id, filename,
+		 err ? "FAIL" : "Ok");
+	return err;
+}
+
+static int build_id_cache__remove_file(const char *filename, struct nsinfo *nsi)
+{
+	char sbuild_id[SBUILD_ID_SIZE];
+	struct build_id bid = { .size = 0, };
+	struct nscookie nsc;
+
+	int err;
+
+	nsinfo__mountns_enter(nsi, &nsc);
+	err = filename__read_build_id(filename, &bid);
+	nsinfo__mountns_exit(&nsc);
+	if (err < 0) {
+		pr_debug("Couldn't read a build-id in %s\n", filename);
+		return -1;
+	}
+
+	build_id__snprintf(&bid, sbuild_id, sizeof(sbuild_id));
+	err = build_id_cache__remove_s(sbuild_id);
+	pr_debug("Removing %s %s: %s\n", sbuild_id, filename,
+		 err ? "FAIL" : "Ok");
+
+	return err;
+}
+
+static int build_id_cache__purge_path(const char *pathname, struct nsinfo *nsi)
+{
+	struct strlist *list;
+	struct str_node *pos;
+	int err;
+
+	err = build_id_cache__list_build_ids(pathname, nsi, &list);
+	if (err)
+		goto out;
+
+	strlist__for_each_entry(pos, list) {
+		err = build_id_cache__remove_s(pos->s);
+		pr_debug("Removing %s %s: %s\n", pos->s, pathname,
+			 err ? "FAIL" : "Ok");
+		if (err)
+			break;
+	}
+	strlist__delete(list);
+
+out:
+	pr_debug("Purging %s: %s\n", pathname, err ? "FAIL" : "Ok");
+
+	return err;
+}
+
+static int build_id_cache__purge_all(void)
+{
+	struct strlist *list;
+	struct str_node *pos;
+	int err = 0;
+	char *buf;
+
+	list = build_id_cache__list_all(false);
+	if (!list) {
+		pr_debug("Failed to get buildids: -%d\n", errno);
+		return -EINVAL;
+	}
+
+	strlist__for_each_entry(pos, list) {
+		buf = build_id_cache__origname(pos->s);
+		err = build_id_cache__remove_s(pos->s);
+		pr_debug("Removing %s (%s): %s\n", buf, pos->s,
+			 err ? "FAIL" : "Ok");
+		free(buf);
+		if (err)
+			break;
+	}
+	strlist__delete(list);
+
+	pr_debug("Purged all: %s\n", err ? "FAIL" : "Ok");
+	return err;
+}
+
+static bool dso__missing_buildid_cache(struct dso *dso, int parm __maybe_unused)
+{
+	char filename[PATH_MAX];
+	struct build_id bid = { .size = 0, };
+	int err;
+
+	if (!dso__build_id_filename(dso, filename, sizeof(filename), false))
+		return true;
+
+	err = filename__read_build_id(filename, &bid);
+	if (err < 0) {
+		if (err == -ENOENT)
+			return false;
+
+		pr_warning("Problems with %s file, consider removing it from the cache\n",
+			   filename);
+	} else if (memcmp(dso__bid(dso)->data, bid.data, bid.size)) {
+		pr_warning("Problems with %s file, consider removing it from the cache\n",
+			   filename);
+	}
+
+	return true;
+}
+
+static int build_id_cache__fprintf_missing(struct perf_session *session, FILE *fp)
+{
+	perf_session__fprintf_dsos_buildid(session, fp, dso__missing_buildid_cache, 0);
+	return 0;
+}
+
+static int build_id_cache__update_file(const char *filename, struct nsinfo *nsi)
+{
+	char sbuild_id[SBUILD_ID_SIZE];
+	struct build_id bid = { .size = 0, };
+	struct nscookie nsc;
+
+	int err;
+
+	nsinfo__mountns_enter(nsi, &nsc);
+	err = filename__read_build_id(filename, &bid);
+	nsinfo__mountns_exit(&nsc);
+	if (err < 0) {
+		pr_debug("Couldn't read a build-id in %s\n", filename);
+		return -1;
+	}
+	err = 0;
+
+	build_id__snprintf(&bid, sbuild_id, sizeof(sbuild_id));
+	if (build_id_cache__cached(sbuild_id))
+		err = build_id_cache__remove_s(sbuild_id);
+
+	if (!err)
+		err = build_id_cache__add_s(sbuild_id, filename, nsi, false,
+					    false);
+
+	pr_debug("Updating %s %s: %s\n", sbuild_id, filename,
+		 err ? "FAIL" : "Ok");
+
+	return err;
+}
+
+static int build_id_cache__show_all(void)
+{
+	struct strlist *bidlist;
+	struct str_node *nd;
+	char *buf;
+
+	bidlist = build_id_cache__list_all(true);
+	if (!bidlist) {
+		pr_debug("Failed to get buildids: -%d\n", errno);
+		return -1;
+	}
+	strlist__for_each_entry(nd, bidlist) {
+		buf = build_id_cache__origname(nd->s);
+		fprintf(stdout, "%s %s\n", nd->s, buf);
+		free(buf);
+	}
+	strlist__delete(bidlist);
+	return 0;
+}
+
+static int perf_buildid_cache_config(const char *var, const char *value, void *cb)
+{
+	struct perf_debuginfod *di = cb;
+
+	if (!strcmp(var, "buildid-cache.debuginfod")) {
+		di->urls = strdup(value);
+		if (!di->urls)
+			return -ENOMEM;
+		di->set = true;
+	}
+
+	return 0;
+}
+
+int cmd_buildid_cache(int argc, const char **argv)
+{
+	struct strlist *list;
+	struct str_node *pos;
+	int ret, ns_id = -1;
+	bool force = false;
+	bool list_files = false;
+	bool opts_flag = false;
+	bool purge_all = false;
+	char const *add_name_list_str = NULL,
+		   *remove_name_list_str = NULL,
+		   *purge_name_list_str = NULL,
+		   *missing_filename = NULL,
+		   *update_name_list_str = NULL,
+		   *kcore_filename = NULL;
+	struct perf_debuginfod debuginfod = { };
+	char sbuf[STRERR_BUFSIZE];
+
+	struct perf_data data = {
+		.mode  = PERF_DATA_MODE_READ,
+	};
+	struct perf_session *session = NULL;
+	struct nsinfo *nsi = NULL;
+
+	const struct option buildid_cache_options[] = {
+	OPT_STRING('a', "add", &add_name_list_str,
+		   "file list", "file(s) to add"),
+	OPT_STRING('k', "kcore", &kcore_filename,
+		   "file", "kcore file to add"),
+	OPT_STRING('r', "remove", &remove_name_list_str, "file list",
+		    "file(s) to remove"),
+	OPT_STRING('p', "purge", &purge_name_list_str, "file list",
+		    "file(s) to remove (remove old caches too)"),
+	OPT_BOOLEAN('P', "purge-all", &purge_all, "purge all cached files"),
+	OPT_BOOLEAN('l', "list", &list_files, "list all cached files"),
+	OPT_STRING('M', "missing", &missing_filename, "file",
+		   "to find missing build ids in the cache"),
+	OPT_BOOLEAN('f', "force", &force, "don't complain, do it"),
+	OPT_STRING('u', "update", &update_name_list_str, "file list",
+		    "file(s) to update"),
+	OPT_STRING_OPTARG_SET(0, "debuginfod", &debuginfod.urls,
+			&debuginfod.set, "debuginfod urls",
+			"Enable debuginfod data retrieval from DEBUGINFOD_URLS or specified urls",
+			"system"),
+	OPT_INCR('v', "verbose", &verbose, "be more verbose"),
+	OPT_INTEGER(0, "target-ns", &ns_id, "target pid for namespace context"),
+	OPT_END()
+	};
+	const char * const buildid_cache_usage[] = {
+		"perf buildid-cache [<options>]",
+		NULL
+	};
+
+	ret = perf_config(perf_buildid_cache_config, &debuginfod);
+	if (ret)
+		return ret;
+
+	argc = parse_options(argc, argv, buildid_cache_options,
+			     buildid_cache_usage, 0);
+
+	opts_flag = add_name_list_str || kcore_filename ||
+		remove_name_list_str || purge_name_list_str ||
+		missing_filename || update_name_list_str ||
+		purge_all;
+
+	if (argc || !(list_files || opts_flag))
+		usage_with_options(buildid_cache_usage, buildid_cache_options);
+
+	perf_debuginfod_setup(&debuginfod);
+
+	/* -l is exclusive. It can not be used with other options. */
+	if (list_files && opts_flag) {
+		usage_with_options_msg(buildid_cache_usage,
+			buildid_cache_options, "-l is exclusive.\n");
+	}
+
+	if (ns_id > 0)
+		nsi = nsinfo__new(ns_id);
+
+	if (missing_filename) {
+		data.path  = missing_filename;
+		data.force = force;
+
+		session = perf_session__new(&data, NULL);
+		if (IS_ERR(session))
+			return PTR_ERR(session);
+	}
+
+	if (symbol__init(session ? perf_session__env(session) : NULL) < 0)
+		goto out;
+
+	setup_pager();
+
+	if (list_files) {
+		ret = build_id_cache__show_all();
+		goto out;
+	}
+
+	if (add_name_list_str) {
+		list = strlist__new(add_name_list_str, NULL);
+		if (list) {
+			strlist__for_each_entry(pos, list)
+				if (build_id_cache__add_file(pos->s, nsi)) {
+					if (errno == EEXIST) {
+						pr_debug("%s already in the cache\n",
+							 pos->s);
+						continue;
+					}
+					pr_warning("Couldn't add %s: %s\n",
+						   pos->s, str_error_r(errno, sbuf, sizeof(sbuf)));
+				}
+
+			strlist__delete(list);
+		}
+	}
+
+	if (remove_name_list_str) {
+		list = strlist__new(remove_name_list_str, NULL);
+		if (list) {
+			strlist__for_each_entry(pos, list)
+				if (build_id_cache__remove_file(pos->s, nsi)) {
+					if (errno == ENOENT) {
+						pr_debug("%s wasn't in the cache\n",
+							 pos->s);
+						continue;
+					}
+					pr_warning("Couldn't remove %s: %s\n",
+						   pos->s, str_error_r(errno, sbuf, sizeof(sbuf)));
+				}
+
+			strlist__delete(list);
+		}
+	}
+
+	if (purge_name_list_str) {
+		list = strlist__new(purge_name_list_str, NULL);
+		if (list) {
+			strlist__for_each_entry(pos, list)
+				if (build_id_cache__purge_path(pos->s, nsi)) {
+					if (errno == ENOENT) {
+						pr_debug("%s wasn't in the cache\n",
+							 pos->s);
+						continue;
+					}
+					pr_warning("Couldn't remove %s: %s\n",
+						   pos->s, str_error_r(errno, sbuf, sizeof(sbuf)));
+				}
+
+			strlist__delete(list);
+		}
+	}
+
+	if (purge_all) {
+		if (build_id_cache__purge_all()) {
+			pr_warning("Couldn't remove some caches. Error: %s.\n",
+				str_error_r(errno, sbuf, sizeof(sbuf)));
+		}
+	}
+
+	if (missing_filename)
+		ret = build_id_cache__fprintf_missing(session, stdout);
+
+	if (update_name_list_str) {
+		list = strlist__new(update_name_list_str, NULL);
+		if (list) {
+			strlist__for_each_entry(pos, list)
+				if (build_id_cache__update_file(pos->s, nsi)) {
+					if (errno == ENOENT) {
+						pr_debug("%s wasn't in the cache\n",
+							 pos->s);
+						continue;
+					}
+					pr_warning("Couldn't update %s: %s\n",
+						   pos->s, str_error_r(errno, sbuf, sizeof(sbuf)));
+				}
+
+			strlist__delete(list);
+		}
+	}
+
+	if (kcore_filename && build_id_cache__add_kcore(kcore_filename, force))
+		pr_warning("Couldn't add %s\n", kcore_filename);
+
+out:
+	perf_session__delete(session);
+	nsinfo__zput(nsi);
+
+	return ret;
+}