perf tools: Back [vdso] DSO with real data

Storing data for VDSO shared object, because we need it for the post
unwind processing.

The VDSO shared object is same for all process on a running system, so
it makes no difference when we store it inside the tracer - perf.

When [vdso] map memory is hit, we retrieve [vdso] DSO image and store it
into temporary file.

During the build-id processing phase, the [vdso] DSO image is stored in
build-id db, and build-id reference is made inside perf.data. The
build-id vdso file object is called '[vdso]'. We don't use temporary
file name which gets removed when record is finished.

During report phase the vdso build-id object is treated as any other
build-id DSO object.

Adding following API for vdso object:

bool is_vdso_map(const char *filename)
- returns true if the filename matches vdso map name

struct dso *vdso__dso_findnew(struct list_head *head)
- find/create proper vdso DSO object

vdso__exit(void)
- removes temporary VDSO image if there's any

This change makes backtrace dwarf post unwind possible from [vdso] maps.

Following output is current report of [vdso] sample dwarf backtrace:

# Overhead Command Shared Object Symbol
# ........ ....... ................. .............................
#
99.52% ex [vdso] [.] 0x00007fff3ace89af
|
--- 0x7fff3ace89af

Following output is new report of [vdso] sample dwarf backtrace:

# Overhead Command Shared Object Symbol
# ........ ....... ................. .............................
#
99.52% ex [vdso] [.] 0x00000000000009af
|
--- 0x7fff3ace89af
main
__libc_start_main
_start

Signed-off-by: Jiri Olsa <[e-mail]>
Acked-by: Peter Zijlstra <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
[ committer note: s/ALIGN/PERF_ALIGN/g to cope with the android build changes ]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Makefile

···
 LIB_H += util/perf_regs.h
 LIB_H += util/unwind.h
 LIB_H += ui/helpline.h
+LIB_H += util/vdso.h
 
 LIB_OBJS += $(OUTPUT)util/abspath.o
 LIB_OBJS += $(OUTPUT)util/alias.o
···
 LIB_OBJS += $(OUTPUT)util/target.o
 LIB_OBJS += $(OUTPUT)util/rblist.o
 LIB_OBJS += $(OUTPUT)util/intlist.o
+LIB_OBJS += $(OUTPUT)util/vdso.o
 
 LIB_OBJS += $(OUTPUT)ui/helpline.o
 LIB_OBJS += $(OUTPUT)ui/hist.o

tools/perf/builtin-buildid-cache.c

···
 	}
 
 	build_id__sprintf(build_id, sizeof(build_id), sbuild_id);
-	err = build_id_cache__add_s(sbuild_id, debugdir, filename, false);
+	err = build_id_cache__add_s(sbuild_id, debugdir, filename,
+				    false, false);
 	if (verbose)
 		pr_info("Adding %s %s: %s\n", sbuild_id, filename,
 			err ? "FAIL" : "Ok");

tools/perf/util/header.c

···
 #include "debug.h"
 #include "cpumap.h"
 #include "pmu.h"
+#include "vdso.h"
 
 static bool no_buildid_cache = false;
 
···
 			continue;		\
 		else
 
+static int write_buildid(char *name, size_t name_len, u8 *build_id,
+			 pid_t pid, u16 misc, int 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 __dsos__write_buildid_table(struct list_head *head, pid_t pid,
 				u16 misc, int fd)
 {
···
 
 	dsos__for_each_with_build_id(pos, head) {
 		int err;
-		struct build_id_event b;
-		size_t len;
+		char  *name;
+		size_t name_len;
 
 		if (!pos->hit)
 			continue;
-		len = pos->long_name_len + 1;
-		len = PERF_ALIGN(len, NAME_ALIGN);
-		memset(&b, 0, sizeof(b));
-		memcpy(&b.build_id, pos->build_id, sizeof(pos->build_id));
-		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;
-		err = write_padded(fd, pos->long_name,
-				   pos->long_name_len + 1, len);
-		if (err < 0)
+
+		if (is_vdso_map(pos->short_name)) {
+			name = (char *) VDSO__MAP_NAME;
+			name_len = sizeof(VDSO__MAP_NAME) + 1;
+		} else {
+			name = pos->long_name;
+			name_len = pos->long_name_len + 1;
+		}
+
+		err = write_buildid(name, name_len, pos->build_id,
+				    pid, misc, fd);
+		if (err)
 			return err;
 	}
 
···
 }
 
 int build_id_cache__add_s(const char *sbuild_id, const char *debugdir,
-			  const char *name, bool is_kallsyms)
+			  const char *name, bool is_kallsyms, bool is_vdso)
 {
 	const size_t size = PATH_MAX;
 	char *realname, *filename = zalloc(size),
 	     *linkname = zalloc(size), *targetname;
 	int len, err = -1;
+	bool slash = is_kallsyms || is_vdso;
 
 	if (is_kallsyms) {
 		if (symbol_conf.kptr_restrict) {
 			pr_debug("Not caching a kptr_restrict'ed /proc/kallsyms\n");
 			return 0;
 		}
-		realname = (char *)name;
+		realname = (char *) name;
 	} else
 		realname = realpath(name, NULL);
 
···
 		goto out_free;
 
 	len = scnprintf(filename, size, "%s%s%s",
-		       debugdir, is_kallsyms ? "/" : "", realname);
+		       debugdir, slash ? "/" : "",
+		       is_vdso ? VDSO__MAP_NAME : realname);
 	if (mkdir_p(filename, 0755))
 		goto out_free;
 
···
 
 static int build_id_cache__add_b(const u8 *build_id, size_t build_id_size,
 				 const char *name, const char *debugdir,
-				 bool is_kallsyms)
+				 bool is_kallsyms, bool is_vdso)
 {
 	char sbuild_id[BUILD_ID_SIZE * 2 + 1];
 
 	build_id__sprintf(build_id, build_id_size, sbuild_id);
 
-	return build_id_cache__add_s(sbuild_id, debugdir, name, is_kallsyms);
+	return build_id_cache__add_s(sbuild_id, debugdir, name,
+				     is_kallsyms, is_vdso);
 }
 
 int build_id_cache__remove_s(const char *sbuild_id, const char *debugdir)
···
 static int dso__cache_build_id(struct dso *dso, const char *debugdir)
 {
 	bool is_kallsyms = dso->kernel && dso->long_name[0] != '/';
+	bool is_vdso = is_vdso_map(dso->short_name);
 
 	return build_id_cache__add_b(dso->build_id, sizeof(dso->build_id),
-				     dso->long_name, debugdir, is_kallsyms);
+				     dso->long_name, debugdir,
+				     is_kallsyms, is_vdso);
 }
 
 static int __dsos__cache_build_ids(struct list_head *head, const char *debugdir)

tools/perf/util/header.h

···
 int perf_header__fprintf_info(struct perf_session *s, FILE *fp, bool full);
 
 int build_id_cache__add_s(const char *sbuild_id, const char *debugdir,
-			  const char *name, bool is_kallsyms);
+			  const char *name, bool is_kallsyms, bool is_vdso);
 int build_id_cache__remove_s(const char *sbuild_id, const char *debugdir);
 
 int perf_event__synthesize_attr(struct perf_tool *tool,

tools/perf/util/map.c

···
 #include "map.h"
 #include "thread.h"
 #include "strlist.h"
+#include "vdso.h"
 
 const char *map_type__name[MAP__NR_TYPES] = {
 	[MAP__FUNCTION] = "Functions",
···
 static inline int is_no_dso_memory(const char *filename)
 {
 	return !strcmp(filename, "[stack]") ||
-	       !strcmp(filename, "[vdso]")  ||
 	       !strcmp(filename, "[heap]");
 }
 
···
 	if (self != NULL) {
 		char newfilename[PATH_MAX];
 		struct dso *dso;
-		int anon, no_dso;
+		int anon, no_dso, vdso;
 
 		anon = is_anon_memory(filename);
+		vdso = is_vdso_map(filename);
 		no_dso = is_no_dso_memory(filename);
 
 		if (anon) {
···
 			filename = newfilename;
 		}
 
-		dso = __dsos__findnew(dsos__list, filename);
+		if (vdso) {
+			pgoff = 0;
+			dso = vdso__dso_findnew(dsos__list);
+		} else
+			dso = __dsos__findnew(dsos__list, filename);
+
 		if (dso == NULL)
 			goto out_delete;
 

tools/perf/util/session.c

···
 #include "event-parse.h"
 #include "perf_regs.h"
 #include "unwind.h"
+#include "vdso.h"
 
 static int perf_session__open(struct perf_session *self, bool force)
 {
···
 	machine__exit(&self->host_machine);
 	close(self->fd);
 	free(self);
+	vdso__exit();
 }
 
 void machine__remove_thread(struct machine *self, struct thread *th)

tools/perf/util/vdso.c

···
+
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <linux/kernel.h>
+
+#include "vdso.h"
+#include "util.h"
+#include "symbol.h"
+#include "linux/string.h"
+
+static bool vdso_found;
+static char vdso_file[] = "/tmp/perf-vdso.so-XXXXXX";
+
+static int find_vdso_map(void **start, void **end)
+{
+	FILE *maps;
+	char line[128];
+	int found = 0;
+
+	maps = fopen("/proc/self/maps", "r");
+	if (!maps) {
+		pr_err("vdso: cannot open maps\n");
+		return -1;
+	}
+
+	while (!found && fgets(line, sizeof(line), maps)) {
+		int m = -1;
+
+		/* We care only about private r-x mappings. */
+		if (2 != sscanf(line, "%p-%p r-xp %*x %*x:%*x %*u %n",
+				start, end, &m))
+			continue;
+		if (m < 0)
+			continue;
+
+		if (!strncmp(&line[m], VDSO__MAP_NAME,
+			     sizeof(VDSO__MAP_NAME) - 1))
+			found = 1;
+	}
+
+	fclose(maps);
+	return !found;
+}
+
+static char *get_file(void)
+{
+	char *vdso = NULL;
+	char *buf = NULL;
+	void *start, *end;
+	size_t size;
+	int fd;
+
+	if (vdso_found)
+		return vdso_file;
+
+	if (find_vdso_map(&start, &end))
+		return NULL;
+
+	size = end - start;
+
+	buf = memdup(start, size);
+	if (!buf)
+		return NULL;
+
+	fd = mkstemp(vdso_file);
+	if (fd < 0)
+		goto out;
+
+	if (size == (size_t) write(fd, buf, size))
+		vdso = vdso_file;
+
+	close(fd);
+
+ out:
+	free(buf);
+
+	vdso_found = (vdso != NULL);
+	return vdso;
+}
+
+void vdso__exit(void)
+{
+	if (vdso_found)
+		unlink(vdso_file);
+}
+
+struct dso *vdso__dso_findnew(struct list_head *head)
+{
+	struct dso *dso = dsos__find(head, VDSO__MAP_NAME);
+
+	if (!dso) {
+		char *file;
+
+		file = get_file();
+		if (!file)
+			return NULL;
+
+		dso = dso__new(VDSO__MAP_NAME);
+		if (dso != NULL) {
+			dsos__add(head, dso);
+			dso__set_long_name(dso, file);
+		}
+	}
+
+	return dso;
+}

tools/perf/util/vdso.h

···
+#ifndef __PERF_VDSO__
+#define __PERF_VDSO__
+
+#include <linux/types.h>
+#include <string.h>
+#include <stdbool.h>
+
+#define VDSO__MAP_NAME "[vdso]"
+
+static inline bool is_vdso_map(const char *filename)
+{
+	return !strcmp(filename, VDSO__MAP_NAME);
+}
+
+struct dso *vdso__dso_findnew(struct list_head *head);
+void vdso__exit(void);
+
+#endif /* __PERF_VDSO__ */