[PATCH -tip v2 0/2] perf-probe: Dwarf support for uprobes

Masami Hiramatsu
2013-12-26T06:03:52Z

Hi,

Here is the 2nd version of the series of perf-probe patches
which adds basic dwarf(debuginfo) support for uprobes.

Currently perf-probe doesn't support debuginfo for uprobes.
The lack of the debuginfo support for uprobes sometimes
confuses users (or makes them cry) because they can't use
perf-probe as for kprobes case, and that is not what I hope.

So I tried to add debuginfo support for uprobes on
perf-probe. Actually, this is not completely done yet.
We still need to add some features for make it perfect.
However, this series can provide minimum debuginfo
support for uprobes.

For example, the following command shows the probe-able lines of
a given user space function. Something that so far was only
available in the 'perf probe' tool for kernel space functions:
----
# ./perf probe -x perf --line map__load
<map__load@/home/fedora/ksrc/linux-2.6/tools/perf/util/map.c:0>
0 int map__load(struct map *map, symbol_filter_t filter)
1 {
2 const char *name = map->dso->long_name;
int nr;

5 if (dso__loaded(map->dso, map->type))
6 return 0;

8 nr = dso__load(map->dso, map, filter);
9 if (nr < 0) {
10 if (map->dso->has_build_id) {
----

And this shows the available variables at the given line of
the function.
----
# ./perf probe -x perf --vars map__load:8
Available variables at map__load:8
@<map__load+96>
char* name
struct map* map
symbol_filter_t filter
@<map__find_symbol+112>
char* name
symbol_filter_t filter
@<map__find_symbol_by_name+136>
char* name
symbol_filter_t filter
@<map_groups__find_symbol_by_name+176>
char* name
struct map* map
symbol_filter_t filter
----

At last, we can now define a probe(s) with all available
variables on the given line.
----
# ./perf probe -x perf --add 'map__load:8 $vars'

Added new events:
probe_perf:map__load (on map__load:8 with $vars)
probe_perf:map__load_1 (on map__load:8 with $vars)
probe_perf:map__load_2 (on map__load:8 with $vars)
probe_perf:map__load_3 (on map__load:8 with $vars)

You can now use it in all perf tools, such as:

perf record -e probe_perf:map__load_3 -aR sleep 1
----

To complete this requires Namhyung's uprobe
fetch-method updates which is almost done on LKML.

TODO:
- Convert data symbol name in arguments to address
offset value.
- Support distro style debuginfo path (/usr/lib/debug/...)
- Support --list to show actual lines and executable names.

Changes from previous one:
- Fix not to print null string.
- Allocate memory for given path/module name everytime.
- Fix patch descriptions.
- Add examples in the patch description.
- Use .text section start address and dwarf symbol address
for calculating the offset of given symbol, instead of
searching the symbol in symtab again.
With this change, we can safely handle multiple local
function instances (e.g. scnprintf in perf).

---

Masami Hiramatsu (2):
[CLEANUP] perf-probe: Expand given path to absolute path
perf-probe: Support basic dwarf-based operations on uprobe events

tools/perf/builtin-probe.c | 18 ++++
tools/perf/util/probe-event.c | 162 ++++++++++++++++++++++++++++++++++------
tools/perf/util/probe-event.h | 1
tools/perf/util/probe-finder.c | 1
4 files changed, 155 insertions(+), 27 deletions(-)

--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com