1 files changed, 876 insertions, 0 deletions

diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
new file mode 100644
index 000000000..1d352621b
--- /dev/null
+++ b/tools/perf/util/build-id.c
@@ -0,0 +1,876 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * build-id.c
+ *
+ * build-id support
+ *
+ * Copyright (C) 2009, 2010 Red Hat Inc.
+ * Copyright (C) 2009, 2010 Arnaldo Carvalho de Melo <acme@redhat.com>
+ */
+#include "util.h"
+#include <dirent.h>
+#include <errno.h>
+#include <stdio.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include "build-id.h"
+#include "event.h"
+#include "symbol.h"
+#include "thread.h"
+#include <linux/kernel.h>
+#include "debug.h"
+#include "session.h"
+#include "tool.h"
+#include "header.h"
+#include "vdso.h"
+#include "path.h"
+#include "probe-file.h"
+#include "strlist.h"
+
+#include "sane_ctype.h"
+
+static bool no_buildid_cache;
+
+int build_id__mark_dso_hit(struct perf_tool *tool __maybe_unused,
+			   union perf_event *event,
+			   struct perf_sample *sample,
+			   struct perf_evsel *evsel __maybe_unused,
+			   struct machine *machine)
+{
+	struct addr_location al;
+	struct thread *thread = machine__findnew_thread(machine, sample->pid,
+							sample->tid);
+
+	if (thread == NULL) {
+		pr_err("problem processing %d event, skipping it.\n",
+			event->header.type);
+		return -1;
+	}
+
+	if (thread__find_map(thread, sample->cpumode, sample->ip, &al))
+		al.map->dso->hit = 1;
+
+	thread__put(thread);
+	return 0;
+}
+
+static int perf_event__exit_del_thread(struct perf_tool *tool __maybe_unused,
+				       union perf_event *event,
+				       struct perf_sample *sample
+				       __maybe_unused,
+				       struct machine *machine)
+{
+	struct thread *thread = machine__findnew_thread(machine,
+							event->fork.pid,
+							event->fork.tid);
+
+	dump_printf("(%d:%d):(%d:%d)\n", event->fork.pid, event->fork.tid,
+		    event->fork.ppid, event->fork.ptid);
+
+	if (thread) {
+		machine__remove_thread(machine, thread);
+		thread__put(thread);
+	}
+
+	return 0;
+}
+
+struct perf_tool build_id__mark_dso_hit_ops = {
+	.sample	= build_id__mark_dso_hit,
+	.mmap	= perf_event__process_mmap,
+	.mmap2	= perf_event__process_mmap2,
+	.fork	= perf_event__process_fork,
+	.exit	= perf_event__exit_del_thread,
+	.attr		 = perf_event__process_attr,
+	.build_id	 = perf_event__process_build_id,
+	.ordered_events	 = true,
+};
+
+int build_id__sprintf(const u8 *build_id, int len, char *bf)
+{
+	char *bid = bf;
+	const u8 *raw = build_id;
+	int i;
+
+	for (i = 0; i < len; ++i) {
+		sprintf(bid, "%02x", *raw);
+		++raw;
+		bid += 2;
+	}
+
+	return (bid - bf) + 1;
+}
+
+int sysfs__sprintf_build_id(const char *root_dir, char *sbuild_id)
+{
+	char notes[PATH_MAX];
+	u8 build_id[BUILD_ID_SIZE];
+	int ret;
+
+	if (!root_dir)
+		root_dir = "";
+
+	scnprintf(notes, sizeof(notes), "%s/sys/kernel/notes", root_dir);
+
+	ret = sysfs__read_build_id(notes, build_id, sizeof(build_id));
+	if (ret < 0)
+		return ret;
+
+	return build_id__sprintf(build_id, sizeof(build_id), sbuild_id);
+}
+
+int filename__sprintf_build_id(const char *pathname, char *sbuild_id)
+{
+	u8 build_id[BUILD_ID_SIZE];
+	int ret;
+
+	ret = filename__read_build_id(pathname, build_id, sizeof(build_id));
+	if (ret < 0)
+		return ret;
+	else if (ret != sizeof(build_id))
+		return -EINVAL;
+
+	return build_id__sprintf(build_id, sizeof(build_id), sbuild_id);
+}
+
+/* asnprintf consolidates asprintf and snprintf */
+static int asnprintf(char **strp, size_t size, const char *fmt, ...)
+{
+	va_list ap;
+	int ret;
+
+	if (!strp)
+		return -EINVAL;
+
+	va_start(ap, fmt);
+	if (*strp)
+		ret = vsnprintf(*strp, size, fmt, ap);
+	else
+		ret = vasprintf(strp, fmt, ap);
+	va_end(ap);
+
+	return ret;
+}
+
+char *build_id_cache__kallsyms_path(const char *sbuild_id, char *bf,
+				    size_t size)
+{
+	bool retry_old = true;
+
+	snprintf(bf, size, "%s/%s/%s/kallsyms",
+		 buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
+retry:
+	if (!access(bf, F_OK))
+		return bf;
+	if (retry_old) {
+		/* Try old style kallsyms cache */
+		snprintf(bf, size, "%s/%s/%s",
+			 buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
+		retry_old = false;
+		goto retry;
+	}
+
+	return NULL;
+}
+
+char *build_id_cache__linkname(const char *sbuild_id, char *bf, size_t size)
+{
+	char *tmp = bf;
+	int ret = asnprintf(&bf, size, "%s/.build-id/%.2s/%s", buildid_dir,
+			    sbuild_id, sbuild_id + 2);
+	if (ret < 0 || (tmp && size < (unsigned int)ret))
+		return NULL;
+	return bf;
+}
+
+/* The caller is responsible to free the returned buffer. */
+char *build_id_cache__origname(const char *sbuild_id)
+{
+	char *linkname;
+	char buf[PATH_MAX];
+	char *ret = NULL, *p;
+	size_t offs = 5;	/* == strlen("../..") */
+	ssize_t len;
+
+	linkname = build_id_cache__linkname(sbuild_id, NULL, 0);
+	if (!linkname)
+		return NULL;
+
+	len = readlink(linkname, buf, sizeof(buf) - 1);
+	if (len <= 0)
+		goto out;
+	buf[len] = '\0';
+
+	/* The link should be "../..<origpath>/<sbuild_id>" */
+	p = strrchr(buf, '/');	/* Cut off the "/<sbuild_id>" */
+	if (p && (p > buf + offs)) {
+		*p = '\0';
+		if (buf[offs + 1] == '[')
+			offs++;	/*
+				 * This is a DSO name, like [kernel.kallsyms].
+				 * Skip the first '/', since this is not the
+				 * cache of a regular file.
+				 */
+		ret = strdup(buf + offs);	/* Skip "../..[/]" */
+	}
+out:
+	free(linkname);
+	return ret;
+}
+
+/* Check if the given build_id cache is valid on current running system */
+static bool build_id_cache__valid_id(char *sbuild_id)
+{
+	char real_sbuild_id[SBUILD_ID_SIZE] = "";
+	char *pathname;
+	int ret = 0;
+	bool result = false;
+
+	pathname = build_id_cache__origname(sbuild_id);
+	if (!pathname)
+		return false;
+
+	if (!strcmp(pathname, DSO__NAME_KALLSYMS))
+		ret = sysfs__sprintf_build_id("/", real_sbuild_id);
+	else if (pathname[0] == '/')
+		ret = filename__sprintf_build_id(pathname, real_sbuild_id);
+	else
+		ret = -EINVAL;	/* Should we support other special DSO cache? */
+	if (ret >= 0)
+		result = (strcmp(sbuild_id, real_sbuild_id) == 0);
+	free(pathname);
+
+	return result;
+}
+
+static const char *build_id_cache__basename(bool is_kallsyms, bool is_vdso,
+					    bool is_debug)
+{
+	return is_kallsyms ? "kallsyms" : (is_vdso ? "vdso" : (is_debug ?
+	    "debug" : "elf"));
+}
+
+char *dso__build_id_filename(const struct dso *dso, char *bf, size_t size,
+			     bool is_debug)
+{
+	bool is_kallsyms = dso__is_kallsyms((struct dso *)dso);
+	bool is_vdso = dso__is_vdso((struct dso *)dso);
+	char sbuild_id[SBUILD_ID_SIZE];
+	char *linkname;
+	bool alloc = (bf == NULL);
+	int ret;
+
+	if (!dso->has_build_id)
+		return NULL;
+
+	build_id__sprintf(dso->build_id, sizeof(dso->build_id), sbuild_id);
+	linkname = build_id_cache__linkname(sbuild_id, NULL, 0);
+	if (!linkname)
+		return NULL;
+
+	/* Check if old style build_id cache */
+	if (is_regular_file(linkname))
+		ret = asnprintf(&bf, size, "%s", linkname);
+	else
+		ret = asnprintf(&bf, size, "%s/%s", linkname,
+			 build_id_cache__basename(is_kallsyms, is_vdso,
+						  is_debug));
+	if (ret < 0 || (!alloc && size < (unsigned int)ret))
+		bf = NULL;
+	free(linkname);
+
+	return bf;
+}
+
+#define dsos__for_each_with_build_id(pos, head)	\
+	list_for_each_entry(pos, head, node)	\
+		if (!pos->has_build_id)		\
+			continue;		\
+		else
+
+static int write_buildid(const char *name, size_t name_len, u8 *build_id,
+			 pid_t pid, u16 misc, struct feat_fd *fd)
+{
+	int err;
+	struct build_id_event b;
+	size_t len;
+
+	len = name_len + 1;
+	len = PERF_ALIGN(len, NAME_ALIGN);
+
+	memset(&b, 0, sizeof(b));
+	memcpy(&b.build_id, build_id, BUILD_ID_SIZE);
+	b.pid = pid;
+	b.header.misc = misc;
+	b.header.size = sizeof(b) + len;
+
+	err = do_write(fd, &b, sizeof(b));
+	if (err < 0)
+		return err;
+
+	return write_padded(fd, name, name_len + 1, len);
+}
+
+static int machine__write_buildid_table(struct machine *machine,
+					struct feat_fd *fd)
+{
+	int err = 0;
+	struct dso *pos;
+	u16 kmisc = PERF_RECORD_MISC_KERNEL,
+	    umisc = PERF_RECORD_MISC_USER;
+
+	if (!machine__is_host(machine)) {
+		kmisc = PERF_RECORD_MISC_GUEST_KERNEL;
+		umisc = PERF_RECORD_MISC_GUEST_USER;
+	}
+
+	dsos__for_each_with_build_id(pos, &machine->dsos.head) {
+		const char *name;
+		size_t name_len;
+		bool in_kernel = false;
+
+		if (!pos->hit && !dso__is_vdso(pos))
+			continue;
+
+		if (dso__is_vdso(pos)) {
+			name = pos->short_name;
+			name_len = pos->short_name_len;
+		} else if (dso__is_kcore(pos)) {
+			name = machine->mmap_name;
+			name_len = strlen(name);
+		} else {
+			name = pos->long_name;
+			name_len = pos->long_name_len;
+		}
+
+		in_kernel = pos->kernel ||
+				is_kernel_module(name,
+					PERF_RECORD_MISC_CPUMODE_UNKNOWN);
+		err = write_buildid(name, name_len, pos->build_id, machine->pid,
+				    in_kernel ? kmisc : umisc, fd);
+		if (err)
+			break;
+	}
+
+	return err;
+}
+
+int perf_session__write_buildid_table(struct perf_session *session,
+				      struct feat_fd *fd)
+{
+	struct rb_node *nd;
+	int err = machine__write_buildid_table(&session->machines.host, fd);
+
+	if (err)
+		return err;
+
+	for (nd = rb_first(&session->machines.guests); nd; nd = rb_next(nd)) {
+		struct machine *pos = rb_entry(nd, struct machine, rb_node);
+		err = machine__write_buildid_table(pos, fd);
+		if (err)
+			break;
+	}
+	return err;
+}
+
+static int __dsos__hit_all(struct list_head *head)
+{
+	struct dso *pos;
+
+	list_for_each_entry(pos, head, node)
+		pos->hit = true;
+
+	return 0;
+}
+
+static int machine__hit_all_dsos(struct machine *machine)
+{
+	return __dsos__hit_all(&machine->dsos.head);
+}
+
+int dsos__hit_all(struct perf_session *session)
+{
+	struct rb_node *nd;
+	int err;
+
+	err = machine__hit_all_dsos(&session->machines.host);
+	if (err)
+		return err;
+
+	for (nd = rb_first(&session->machines.guests); nd; nd = rb_next(nd)) {
+		struct machine *pos = rb_entry(nd, struct machine, rb_node);
+
+		err = machine__hit_all_dsos(pos);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+void disable_buildid_cache(void)
+{
+	no_buildid_cache = true;
+}
+
+static bool lsdir_bid_head_filter(const char *name __maybe_unused,
+				  struct dirent *d)
+{
+	return (strlen(d->d_name) == 2) &&
+		isxdigit(d->d_name[0]) && isxdigit(d->d_name[1]);
+}
+
+static bool lsdir_bid_tail_filter(const char *name __maybe_unused,
+				  struct dirent *d)
+{
+	int i = 0;
+	while (isxdigit(d->d_name[i]) && i < SBUILD_ID_SIZE - 3)
+		i++;
+	return (i == SBUILD_ID_SIZE - 3) && (d->d_name[i] == '\0');
+}
+
+struct strlist *build_id_cache__list_all(bool validonly)
+{
+	struct strlist *toplist, *linklist = NULL, *bidlist;
+	struct str_node *nd, *nd2;
+	char *topdir, *linkdir = NULL;
+	char sbuild_id[SBUILD_ID_SIZE];
+
+	/* for filename__ functions */
+	if (validonly)
+		symbol__init(NULL);
+
+	/* Open the top-level directory */
+	if (asprintf(&topdir, "%s/.build-id/", buildid_dir) < 0)
+		return NULL;
+
+	bidlist = strlist__new(NULL, NULL);
+	if (!bidlist)
+		goto out;
+
+	toplist = lsdir(topdir, lsdir_bid_head_filter);
+	if (!toplist) {
+		pr_debug("Error in lsdir(%s): %d\n", topdir, errno);
+		/* If there is no buildid cache, return an empty list */
+		if (errno == ENOENT)
+			goto out;
+		goto err_out;
+	}
+
+	strlist__for_each_entry(nd, toplist) {
+		if (asprintf(&linkdir, "%s/%s", topdir, nd->s) < 0)
+			goto err_out;
+		/* Open the lower-level directory */
+		linklist = lsdir(linkdir, lsdir_bid_tail_filter);
+		if (!linklist) {
+			pr_debug("Error in lsdir(%s): %d\n", linkdir, errno);
+			goto err_out;
+		}
+		strlist__for_each_entry(nd2, linklist) {
+			if (snprintf(sbuild_id, SBUILD_ID_SIZE, "%s%s",
+				     nd->s, nd2->s) != SBUILD_ID_SIZE - 1)
+				goto err_out;
+			if (validonly && !build_id_cache__valid_id(sbuild_id))
+				continue;
+			if (strlist__add(bidlist, sbuild_id) < 0)
+				goto err_out;
+		}
+		strlist__delete(linklist);
+		zfree(&linkdir);
+	}
+
+out_free:
+	strlist__delete(toplist);
+out:
+	free(topdir);
+
+	return bidlist;
+
+err_out:
+	strlist__delete(linklist);
+	zfree(&linkdir);
+	strlist__delete(bidlist);
+	bidlist = NULL;
+	goto out_free;
+}
+
+static bool str_is_build_id(const char *maybe_sbuild_id, size_t len)
+{
+	size_t i;
+
+	for (i = 0; i < len; i++) {
+		if (!isxdigit(maybe_sbuild_id[i]))
+			return false;
+	}
+	return true;
+}
+
+/* Return the valid complete build-id */
+char *build_id_cache__complement(const char *incomplete_sbuild_id)
+{
+	struct strlist *bidlist;
+	struct str_node *nd, *cand = NULL;
+	char *sbuild_id = NULL;
+	size_t len = strlen(incomplete_sbuild_id);
+
+	if (len >= SBUILD_ID_SIZE ||
+	    !str_is_build_id(incomplete_sbuild_id, len))
+		return NULL;
+
+	bidlist = build_id_cache__list_all(true);
+	if (!bidlist)
+		return NULL;
+
+	strlist__for_each_entry(nd, bidlist) {
+		if (strncmp(nd->s, incomplete_sbuild_id, len) != 0)
+			continue;
+		if (cand) {	/* Error: There are more than 2 candidates. */
+			cand = NULL;
+			break;
+		}
+		cand = nd;
+	}
+	if (cand)
+		sbuild_id = strdup(cand->s);
+	strlist__delete(bidlist);
+
+	return sbuild_id;
+}
+
+char *build_id_cache__cachedir(const char *sbuild_id, const char *name,
+			       struct nsinfo *nsi, bool is_kallsyms,
+			       bool is_vdso)
+{
+	char *realname = (char *)name, *filename;
+	bool slash = is_kallsyms || is_vdso;
+
+	if (!slash) {
+		realname = nsinfo__realpath(name, nsi);
+		if (!realname)
+			return NULL;
+	}
+
+	if (asprintf(&filename, "%s%s%s%s%s", buildid_dir, slash ? "/" : "",
+		     is_vdso ? DSO__NAME_VDSO : realname,
+		     sbuild_id ? "/" : "", sbuild_id ?: "") < 0)
+		filename = NULL;
+
+	if (!slash)
+		free(realname);
+
+	return filename;
+}
+
+int build_id_cache__list_build_ids(const char *pathname, struct nsinfo *nsi,
+				   struct strlist **result)
+{
+	char *dir_name;
+	int ret = 0;
+
+	dir_name = build_id_cache__cachedir(NULL, pathname, nsi, false, false);
+	if (!dir_name)
+		return -ENOMEM;
+
+	*result = lsdir(dir_name, lsdir_no_dot_filter);
+	if (!*result)
+		ret = -errno;
+	free(dir_name);
+
+	return ret;
+}
+
+#if defined(HAVE_LIBELF_SUPPORT) && defined(HAVE_GELF_GETNOTE_SUPPORT)
+static int build_id_cache__add_sdt_cache(const char *sbuild_id,
+					  const char *realname,
+					  struct nsinfo *nsi)
+{
+	struct probe_cache *cache;
+	int ret;
+	struct nscookie nsc;
+
+	cache = probe_cache__new(sbuild_id, nsi);
+	if (!cache)
+		return -1;
+
+	nsinfo__mountns_enter(nsi, &nsc);
+	ret = probe_cache__scan_sdt(cache, realname);
+	nsinfo__mountns_exit(&nsc);
+	if (ret >= 0) {
+		pr_debug4("Found %d SDTs in %s\n", ret, realname);
+		if (probe_cache__commit(cache) < 0)
+			ret = -1;
+	}
+	probe_cache__delete(cache);
+	return ret;
+}
+#else
+#define build_id_cache__add_sdt_cache(sbuild_id, realname, nsi) (0)
+#endif
+
+static char *build_id_cache__find_debug(const char *sbuild_id,
+					struct nsinfo *nsi)
+{
+	char *realname = NULL;
+	char *debugfile;
+	struct nscookie nsc;
+	size_t len = 0;
+
+	debugfile = calloc(1, PATH_MAX);
+	if (!debugfile)
+		goto out;
+
+	len = __symbol__join_symfs(debugfile, PATH_MAX,
+				   "/usr/lib/debug/.build-id/");
+	snprintf(debugfile + len, PATH_MAX - len, "%.2s/%s.debug", sbuild_id,
+		 sbuild_id + 2);
+
+	nsinfo__mountns_enter(nsi, &nsc);
+	realname = realpath(debugfile, NULL);
+	if (realname && access(realname, R_OK))
+		zfree(&realname);
+	nsinfo__mountns_exit(&nsc);
+out:
+	free(debugfile);
+	return realname;
+}
+
+int build_id_cache__add_s(const char *sbuild_id, const char *name,
+			  struct nsinfo *nsi, bool is_kallsyms, bool is_vdso)
+{
+	const size_t size = PATH_MAX;
+	char *realname = NULL, *filename = NULL, *dir_name = NULL,
+	     *linkname = zalloc(size), *tmp;
+	char *debugfile = NULL;
+	int err = -1;
+
+	if (!is_kallsyms) {
+		if (!is_vdso)
+			realname = nsinfo__realpath(name, nsi);
+		else
+			realname = realpath(name, NULL);
+		if (!realname)
+			goto out_free;
+	}
+
+	dir_name = build_id_cache__cachedir(sbuild_id, name, nsi, is_kallsyms,
+					    is_vdso);
+	if (!dir_name)
+		goto out_free;
+
+	/* Remove old style build-id cache */
+	if (is_regular_file(dir_name))
+		if (unlink(dir_name))
+			goto out_free;
+
+	if (mkdir_p(dir_name, 0755))
+		goto out_free;
+
+	/* Save the allocated buildid dirname */
+	if (asprintf(&filename, "%s/%s", dir_name,
+		     build_id_cache__basename(is_kallsyms, is_vdso,
+		     false)) < 0) {
+		filename = NULL;
+		goto out_free;
+	}
+
+	if (access(filename, F_OK)) {
+		if (is_kallsyms) {
+			if (copyfile("/proc/kallsyms", filename))
+				goto out_free;
+		} else if (nsi && nsi->need_setns) {
+			if (copyfile_ns(name, filename, nsi))
+				goto out_free;
+		} else if (link(realname, filename) && errno != EEXIST &&
+				copyfile(name, filename))
+			goto out_free;
+	}
+
+	/* Some binaries are stripped, but have .debug files with their symbol
+	 * table.  Check to see if we can locate one of those, since the elf
+	 * file itself may not be very useful to users of our tools without a
+	 * symtab.
+	 */
+	if (!is_kallsyms && !is_vdso &&
+	    strncmp(".ko", name + strlen(name) - 3, 3)) {
+		debugfile = build_id_cache__find_debug(sbuild_id, nsi);
+		if (debugfile) {
+			zfree(&filename);
+			if (asprintf(&filename, "%s/%s", dir_name,
+			    build_id_cache__basename(false, false, true)) < 0) {
+				filename = NULL;
+				goto out_free;
+			}
+			if (access(filename, F_OK)) {
+				if (nsi && nsi->need_setns) {
+					if (copyfile_ns(debugfile, filename,
+							nsi))
+						goto out_free;
+				} else if (link(debugfile, filename) &&
+						errno != EEXIST &&
+						copyfile(debugfile, filename))
+					goto out_free;
+			}
+		}
+	}
+
+	if (!build_id_cache__linkname(sbuild_id, linkname, size))
+		goto out_free;
+	tmp = strrchr(linkname, '/');
+	*tmp = '\0';
+
+	if (access(linkname, X_OK) && mkdir_p(linkname, 0755))
+		goto out_free;
+
+	*tmp = '/';
+	tmp = dir_name + strlen(buildid_dir) - 5;
+	memcpy(tmp, "../..", 5);
+
+	if (symlink(tmp, linkname) == 0)
+		err = 0;
+
+	/* Update SDT cache : error is just warned */
+	if (realname &&
+	    build_id_cache__add_sdt_cache(sbuild_id, realname, nsi) < 0)
+		pr_debug4("Failed to update/scan SDT cache for %s\n", realname);
+
+out_free:
+	if (!is_kallsyms)
+		free(realname);
+	free(filename);
+	free(debugfile);
+	free(dir_name);
+	free(linkname);
+	return err;
+}
+
+static int build_id_cache__add_b(const u8 *build_id, size_t build_id_size,
+				 const char *name, struct nsinfo *nsi,
+				 bool is_kallsyms, bool is_vdso)
+{
+	char sbuild_id[SBUILD_ID_SIZE];
+
+	build_id__sprintf(build_id, build_id_size, sbuild_id);
+
+	return build_id_cache__add_s(sbuild_id, name, nsi, is_kallsyms,
+				     is_vdso);
+}
+
+bool build_id_cache__cached(const char *sbuild_id)
+{
+	bool ret = false;
+	char *filename = build_id_cache__linkname(sbuild_id, NULL, 0);
+
+	if (filename && !access(filename, F_OK))
+		ret = true;
+	free(filename);
+
+	return ret;
+}
+
+int build_id_cache__remove_s(const char *sbuild_id)
+{
+	const size_t size = PATH_MAX;
+	char *filename = zalloc(size),
+	     *linkname = zalloc(size), *tmp;
+	int err = -1;
+
+	if (filename == NULL || linkname == NULL)
+		goto out_free;
+
+	if (!build_id_cache__linkname(sbuild_id, linkname, size))
+		goto out_free;
+
+	if (access(linkname, F_OK))
+		goto out_free;
+
+	if (readlink(linkname, filename, size - 1) < 0)
+		goto out_free;
+
+	if (unlink(linkname))
+		goto out_free;
+
+	/*
+	 * Since the link is relative, we must make it absolute:
+	 */
+	tmp = strrchr(linkname, '/') + 1;
+	snprintf(tmp, size - (tmp - linkname), "%s", filename);
+
+	if (rm_rf(linkname))
+		goto out_free;
+
+	err = 0;
+out_free:
+	free(filename);
+	free(linkname);
+	return err;
+}
+
+static int dso__cache_build_id(struct dso *dso, struct machine *machine)
+{
+	bool is_kallsyms = dso__is_kallsyms(dso);
+	bool is_vdso = dso__is_vdso(dso);
+	const char *name = dso->long_name;
+
+	if (dso__is_kcore(dso)) {
+		is_kallsyms = true;
+		name = machine->mmap_name;
+	}
+	return build_id_cache__add_b(dso->build_id, sizeof(dso->build_id), name,
+				     dso->nsinfo, is_kallsyms, is_vdso);
+}
+
+static int __dsos__cache_build_ids(struct list_head *head,
+				   struct machine *machine)
+{
+	struct dso *pos;
+	int err = 0;
+
+	dsos__for_each_with_build_id(pos, head)
+		if (dso__cache_build_id(pos, machine))
+			err = -1;
+
+	return err;
+}
+
+static int machine__cache_build_ids(struct machine *machine)
+{
+	return __dsos__cache_build_ids(&machine->dsos.head, machine);
+}
+
+int perf_session__cache_build_ids(struct perf_session *session)
+{
+	struct rb_node *nd;
+	int ret;
+
+	if (no_buildid_cache)
+		return 0;
+
+	if (mkdir(buildid_dir, 0755) != 0 && errno != EEXIST)
+		return -1;
+
+	ret = machine__cache_build_ids(&session->machines.host);
+
+	for (nd = rb_first(&session->machines.guests); nd; nd = rb_next(nd)) {
+		struct machine *pos = rb_entry(nd, struct machine, rb_node);
+		ret |= machine__cache_build_ids(pos);
+	}
+	return ret ? -1 : 0;
+}
+
+static bool machine__read_build_ids(struct machine *machine, bool with_hits)
+{
+	return __dsos__read_build_ids(&machine->dsos.head, with_hits);
+}
+
+bool perf_session__read_build_ids(struct perf_session *session, bool with_hits)
+{
+	struct rb_node *nd;
+	bool ret = machine__read_build_ids(&session->machines.host, with_hits);
+
+	for (nd = rb_first(&session->machines.guests); nd; nd = rb_next(nd)) {
+		struct machine *pos = rb_entry(nd, struct machine, rb_node);
+		ret |= machine__read_build_ids(pos, with_hits);
+	}
+
+	return ret;
+}