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

From: Masami Hiramatsu
Date: Fri Sep 18 2020 - 04:01:27 EST


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
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@xxxxxxxxxx>