[PATCH v2 0/2] perf probe: Support debuginfod client

[PATCH v2 0/2] perf probe: Support debuginfod client

[Masami Hiramatsu]

Hi,

Here is the 2nd version of a series to enable debuginfod support on
perf probe command. This allows users to access debuginfo binary
from remote device. 

In this version I fixed a build error when libdebuginfod is not
installed ([2/2]).


Since the perf-probe heavily depends on the debuginfo, debuginfod
gives us many benefits on the perf probe command on remote
machine, especially for the embedded devices.

Here is an example (copied from [2/2])

1. at first you need to start debuginfod on the host machine.
   -F option scans local debuginfo binary. (You don't need to pass
   the source tree, but you must keep the source tree untouched)

  (host) $ cd PATH/TO/KBUILD/DIR/
  (host) $ debuginfod -F .
  ...

2. In the remote machine, you need to set DEBUGINFOD_URLS.
   debuginfod uses 8002 tcp port.

  (remote) # export DEBUGINFOD_URLS="http://$HOST_IP:8002/"

3. Then you can use the perf probe (it can refer the source code)

  (remote) # perf probe -L vfs_read
  <vfs_read@...>
        0  ssize_t vfs_read(struct file *file, char __user *buf, size_t count, loff_t *pos)
           {
        2         ssize_t ret;

                  if (!(file->f_mode & FMODE_READ))
                          return -EBADF;
        6         if (!(file->f_mode & FMODE_CAN_READ))
                          return -EINVAL;
        8         if (unlikely(!access_ok(buf, count)))
                          return -EFAULT;

       11         ret = rw_verify_area(READ, file, pos, count);
       12         if (ret)
                          return ret;
                  if (count > MAX_RW_COUNT)
  ...

  (remote) # perf probe -a "vfs_read count"
  Added new event:
    probe:vfs_read       (on vfs_read with count)

  (remote) # perf probe -l
    probe:vfs_read       (on vfs_read@ksrc/linux/fs/read_write.c with count)



Thank you,

---

Masami Hiramatsu (2):
      perf probe: Fix to adjust symbol address with correct reloc_sym address
      perf probe: Fall back to debuginfod query if debuginfo and source not found


 tools/perf/util/probe-event.c  |   66 ++++++++++++++++++++++++++++++++++++++--
 tools/perf/util/probe-finder.c |   61 ++++++++++++++++++++++++++++++++++---
 tools/perf/util/probe-finder.h |    7 +++-
 3 files changed, 123 insertions(+), 11 deletions(-)

--
Masami Hiramatsu (Linaro) <mhiramat@kernel.org>

[PATCH v2 1/2] perf probe: Fix to adjust symbol address with correct reloc_sym address

[Masami Hiramatsu]

Perf probe uses ref_reloc_sym to adjust symbol offset address
from debuginfo address or ref_reloc_sym based address, but
that is misused the reloc_sym->addr and reloc_sym->unrelocated_addr.
If map is not relocated (map->reloc == 0), we can use reloc_sym->addr
as unrelocated address instead of reloc_sym->unrelocated_addr.

This usually may not happen. If we have a non-stripped elf
binary, we will use it for map and debuginfo, if not, we use only
kallsyms without debuginfo. Thus, the map is always relocated (elf
and dwarf binary) or not relocated (kallsyms).

However, if we will allow the combination of debuginfo and kallsyms
based map (like using debuginfod), we have to check the map->reloc
and choose the collect address of reloc_sym.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 tools/perf/util/probe-event.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 99d36ac77c08..17831f186ab5 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -129,9 +129,10 @@ static int kernel_get_symbol_address_by_name(const char *name, u64 *addr,
 	struct map *map;
 
 	/* ref_reloc_sym is just a label. Need a special fix*/
-	reloc_sym = kernel_get_ref_reloc_sym(NULL);
+	reloc_sym = kernel_get_ref_reloc_sym(&map);
 	if (reloc_sym && strcmp(name, reloc_sym->name) == 0)
-		*addr = (reloc) ? reloc_sym->addr : reloc_sym->unrelocated_addr;
+		*addr = (!map->reloc || reloc) ? reloc_sym->addr :
+			reloc_sym->unrelocated_addr;
 	else {
 		sym = machine__find_kernel_symbol_by_name(host_machine, name, &map);
 		if (!sym)
@@ -795,7 +796,8 @@ post_process_kernel_probe_trace_events(struct probe_trace_event *tevs,
 			free(tevs[i].point.symbol);
 		tevs[i].point.symbol = tmp;
 		tevs[i].point.offset = tevs[i].point.address -
-				       reloc_sym->unrelocated_addr;
+			(map->reloc ? reloc_sym->unrelocated_addr :
+				      reloc_sym->addr);
 	}
 	return skipped;
 }

[PATCH v2 2/2] perf probe: Fall back to debuginfod query if debuginfo and source not found

[Masami Hiramatsu]

Since the perf-probe heavily depends on the debuginfo, debuginfod
gives us many benefits on the perf probe command on remote machine.
Especially, this will be helpful for the embedded devices which will
not have enough storage, or boot with a cross-build kernel whose
source code is in the host machine.
This will work as similar to the commit c7a14fdcb3fa ("perf build-ids:
Fall back to debuginfod query if debuginfo not found")

Tested with:

  (host) $ cd PATH/TO/KBUILD/DIR/
  (host) $ debuginfod -F .
  ...

  (remote) # perf probe -L vfs_read
  Failed to find the path for the kernel: No such file or directory
    Error: Failed to show lines.

  (remote) # export DEBUGINFOD_URLS="http://$HOST_IP:8002/"
  (remote) # perf probe -L vfs_read
  <vfs_read@...>
        0  ssize_t vfs_read(struct file *file, char __user *buf, size_t count, loff_t *pos)
           {
        2         ssize_t ret;

                  if (!(file->f_mode & FMODE_READ))
                          return -EBADF;
        6         if (!(file->f_mode & FMODE_CAN_READ))
                          return -EINVAL;
        8         if (unlikely(!access_ok(buf, count)))
                          return -EFAULT;

       11         ret = rw_verify_area(READ, file, pos, count);
       12         if (ret)
                          return ret;
                  if (count > MAX_RW_COUNT)
  ...

  (remote) # perf probe -a "vfs_read count"
  Added new event:
    probe:vfs_read       (on vfs_read with count)

  (remote) # perf probe -l
    probe:vfs_read       (on vfs_read@ksrc/linux/fs/read_write.c with count)


Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
 Changes in v2:
  - Fix build error when libdebuginfod is not detected.
---
 tools/perf/util/probe-event.c  |   58 +++++++++++++++++++++++++++++++++++++-
 tools/perf/util/probe-finder.c |   61 +++++++++++++++++++++++++++++++++++++---
 tools/perf/util/probe-finder.h |    7 +++--
 3 files changed, 118 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 17831f186ab5..3a1b58a92673 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -43,6 +43,10 @@
 #include <linux/ctype.h>
 #include <linux/zalloc.h>
 
+#ifdef HAVE_DEBUGINFOD_SUPPORT
+#include <elfutils/debuginfod.h>
+#endif
+
 #define PERFPROBE_GROUP "probe"
 
 bool probe_event_dry_run;	/* Dry run flag */
@@ -338,6 +342,8 @@ static int kernel_get_module_dso(const char *module, struct dso **pdso)
 
 	map = machine__kernel_map(host_machine);
 	dso = map->dso;
+	if (!dso->has_build_id)
+		dso__read_running_kernel_build_id(dso, host_machine);
 
 	vmlinux_name = symbol_conf.vmlinux_name;
 	dso->load_errno = 0;
@@ -453,6 +459,49 @@ static int get_alternative_line_range(struct debuginfo *dinfo,
 	return ret;
 }
 
+#ifdef HAVE_DEBUGINFOD_SUPPORT
+static struct debuginfo *open_from_debuginfod(struct dso *dso, struct nsinfo *nsi,
+					      bool silent)
+{
+	debuginfod_client *c = debuginfod_begin();
+	char sbuild_id[SBUILD_ID_SIZE + 1];
+	struct debuginfo *ret = NULL;
+	struct nscookie nsc;
+	char *path;
+	int fd;
+
+	if (!c)
+		return NULL;
+
+	build_id__sprintf(dso->build_id, BUILD_ID_SIZE, sbuild_id);
+	fd = debuginfod_find_debuginfo(c, (const unsigned char *)sbuild_id,
+					0, &path);
+	if (fd >= 0)
+		close(fd);
+	debuginfod_end(c);
+	if (fd < 0) {
+		if (!silent)
+			pr_debug("Failed to find debuginfo in debuginfod.\n");
+		return NULL;
+	}
+	if (!silent)
+		pr_debug("Load debuginfo from debuginfod (%s)\n", path);
+
+	nsinfo__mountns_enter(nsi, &nsc);
+	ret = debuginfo__new((const char *)path);
+	nsinfo__mountns_exit(&nsc);
+	return ret;
+}
+#else
+static inline
+struct debuginfo *open_from_debuginfod(struct dso *dso __maybe_unused,
+				       struct nsinfo *nsi __maybe_unused,
+				       bool silent __maybe_unused)
+{
+	return NULL;
+}
+#endif
+
 /* Open new debuginfo of given module */
 static struct debuginfo *open_debuginfo(const char *module, struct nsinfo *nsi,
 					bool silent)
@@ -472,6 +521,10 @@ static struct debuginfo *open_debuginfo(const char *module, struct nsinfo *nsi,
 					strcpy(reason, "(unknown)");
 			} else
 				dso__strerror_load(dso, reason, STRERR_BUFSIZE);
+			if (dso)
+				ret = open_from_debuginfod(dso, nsi, silent);
+			if (ret)
+				return ret;
 			if (!silent) {
 				if (module)
 					pr_err("Module %s is not loaded, please specify its full path name.\n", module);
@@ -959,6 +1012,7 @@ static int __show_line_range(struct line_range *lr, const char *module,
 	int ret;
 	char *tmp;
 	char sbuf[STRERR_BUFSIZE];
+	char sbuild_id[SBUILD_ID_SIZE] = "";
 
 	/* Search a line range */
 	dinfo = open_debuginfo(module, NULL, false);
@@ -971,6 +1025,8 @@ static int __show_line_range(struct line_range *lr, const char *module,
 		if (!ret)
 			ret = debuginfo__find_line_range(dinfo, lr);
 	}
+	if (dinfo->build_id)
+		build_id__sprintf(dinfo->build_id, BUILD_ID_SIZE, sbuild_id);
 	debuginfo__delete(dinfo);
 	if (ret == 0 || ret == -ENOENT) {
 		pr_warning("Specified source line is not found.\n");
@@ -982,7 +1038,7 @@ static int __show_line_range(struct line_range *lr, const char *module,
 
 	/* Convert source file path */
 	tmp = lr->path;
-	ret = get_real_path(tmp, lr->comp_dir, &lr->path);
+	ret = find_source_path(tmp, sbuild_id, lr->comp_dir, &lr->path);
 
 	/* Free old path when new path is assigned */
 	if (tmp != lr->path)
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 659024342e9a..6eddf7be8293 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -31,6 +31,10 @@
 #include "probe-file.h"
 #include "string2.h"
 
+#ifdef HAVE_DEBUGINFOD_SUPPORT
+#include <elfutils/debuginfod.h>
+#endif
+
 /* Kprobe tracer basic type is up to u64 */
 #define MAX_BASIC_TYPE_BITS	64
 
@@ -51,6 +55,7 @@ static const Dwfl_Callbacks offline_callbacks = {
 static int debuginfo__init_offline_dwarf(struct debuginfo *dbg,
 					 const char *path)
 {
+	GElf_Addr dummy;
 	int fd;
 
 	fd = open(path, O_RDONLY);
@@ -70,6 +75,8 @@ static int debuginfo__init_offline_dwarf(struct debuginfo *dbg,
 	if (!dbg->dbg)
 		goto error;
 
+	dwfl_module_build_id(dbg->mod, &dbg->build_id, &dummy);
+
 	dwfl_report_end(dbg->dwfl, NULL, NULL);
 
 	return 0;
@@ -942,6 +949,7 @@ static int probe_point_lazy_walker(const char *fname, int lineno,
 /* Find probe points from lazy pattern  */
 static int find_probe_point_lazy(Dwarf_Die *sp_die, struct probe_finder *pf)
 {
+	char sbuild_id[SBUILD_ID_SIZE] = "";
 	int ret = 0;
 	char *fpath;
 
@@ -949,7 +957,10 @@ static int find_probe_point_lazy(Dwarf_Die *sp_die, struct probe_finder *pf)
 		const char *comp_dir;
 
 		comp_dir = cu_get_comp_dir(&pf->cu_die);
-		ret = get_real_path(pf->fname, comp_dir, &fpath);
+		if (pf->dbg->build_id)
+			build_id__sprintf(pf->dbg->build_id,
+					BUILD_ID_SIZE, sbuild_id);
+		ret = find_source_path(pf->fname, sbuild_id, comp_dir, &fpath);
 		if (ret < 0) {
 			pr_warning("Failed to find source file path.\n");
 			return ret;
@@ -1448,7 +1459,7 @@ int debuginfo__find_trace_events(struct debuginfo *dbg,
 				 struct probe_trace_event **tevs)
 {
 	struct trace_event_finder tf = {
-			.pf = {.pev = pev, .callback = add_probe_trace_event},
+			.pf = {.pev = pev, .dbg = dbg, .callback = add_probe_trace_event},
 			.max_tevs = probe_conf.max_probes, .mod = dbg->mod};
 	int ret, i;
 
@@ -1618,7 +1629,7 @@ int debuginfo__find_available_vars_at(struct debuginfo *dbg,
 				      struct variable_list **vls)
 {
 	struct available_var_finder af = {
-			.pf = {.pev = pev, .callback = add_available_vars},
+			.pf = {.pev = pev, .dbg = dbg, .callback = add_available_vars},
 			.mod = dbg->mod,
 			.max_vls = probe_conf.max_probes};
 	int ret;
@@ -1973,17 +1984,57 @@ int debuginfo__find_line_range(struct debuginfo *dbg, struct line_range *lr)
 	return (ret < 0) ? ret : lf.found;
 }
 
+#ifdef HAVE_DEBUGINFOD_SUPPORT
+/* debuginfod doesn't require the comp_dir but buildid is required */
+static int get_source_from_debuginfod(const char *raw_path,
+				const char *sbuild_id, char **new_path)
+{
+	debuginfod_client *c = debuginfod_begin();
+	const char *p = raw_path;
+	int fd;
+
+	if (!c)
+		return -ENOMEM;
+
+	fd = debuginfod_find_source(c, (const unsigned char *)sbuild_id,
+				0, p, new_path);
+	pr_debug("Search %s from debuginfod -> %d\n", p, fd);
+	if (fd >= 0)
+		close(fd);
+	debuginfod_end(c);
+	if (fd < 0) {
+		pr_debug("Failed to find %s in debuginfod (%s)\n",
+			raw_path, sbuild_id);
+		return -ENOENT;
+	}
+	pr_debug("Got a source %s\n", *new_path);
+
+	return 0;
+}
+#else
+static inline int get_source_from_debuginfod(const char *raw_path __maybe_unused,
+				const char *sbuild_id __maybe_unused,
+				char **new_path __maybe_unused)
+{
+	return -ENOTSUP;
+}
+#endif
 /*
  * Find a src file from a DWARF tag path. Prepend optional source path prefix
  * and chop off leading directories that do not exist. Result is passed back as
  * a newly allocated path on success.
  * Return 0 if file was found and readable, -errno otherwise.
  */
-int get_real_path(const char *raw_path, const char *comp_dir,
-			 char **new_path)
+int find_source_path(const char *raw_path, const char *sbuild_id,
+		const char *comp_dir, char **new_path)
 {
 	const char *prefix = symbol_conf.source_prefix;
 
+	if (sbuild_id && !prefix) {
+		if (!get_source_from_debuginfod(raw_path, sbuild_id, new_path))
+			return 0;
+	}
+
 	if (!prefix) {
 		if (raw_path[0] != '/' && comp_dir)
 			/* If not an absolute path, try to use comp_dir */
diff --git a/tools/perf/util/probe-finder.h b/tools/perf/util/probe-finder.h
index 11be10080613..2febb5875678 100644
--- a/tools/perf/util/probe-finder.h
+++ b/tools/perf/util/probe-finder.h
@@ -4,6 +4,7 @@
 
 #include <stdbool.h>
 #include "intlist.h"
+#include "build-id.h"
 #include "probe-event.h"
 #include <linux/ctype.h>
 
@@ -32,6 +33,7 @@ struct debuginfo {
 	Dwfl_Module	*mod;
 	Dwfl		*dwfl;
 	Dwarf_Addr	bias;
+	const unsigned char	*build_id;
 };
 
 /* This also tries to open distro debuginfo */
@@ -59,11 +61,12 @@ int debuginfo__find_available_vars_at(struct debuginfo *dbg,
 				      struct variable_list **vls);
 
 /* Find a src file from a DWARF tag path */
-int get_real_path(const char *raw_path, const char *comp_dir,
-			 char **new_path);
+int find_source_path(const char *raw_path, const char *sbuild_id,
+		     const char *comp_dir, char **new_path);
 
 struct probe_finder {
 	struct perf_probe_event	*pev;		/* Target probe event */
+	struct debuginfo	*dbg;
 
 	/* Callback when a probe point is found */
 	int (*callback)(Dwarf_Die *sc_die, struct probe_finder *pf);