xref: /aosp_15_r20/external/bcc/tools/shmsnoop_example.txt (revision 387f9dfdfa2baef462e92476d413c7bc2470293e)

Demonstrations of shmsnoop, the Linux eBPF/bcc version.

shmsnoop traces shm*() syscalls, for example:

# ./shmsnoop.py
PID    COMM                SYS              RET ARGs
19813  server           SHMGET            10000 key: 0x78020001, size: 20, shmflg: 0x3b6 (IPC_CREAT|0666)
19813  server            SHMAT     7f1cf8b1f000 shmid: 0x10000, shmaddr: 0x0, shmflg: 0x0
19816  client           SHMGET            10000 key: 0x78020001, size: 20, shmflg: 0x1b6 (0666)
19816  client            SHMAT     7f4fd8ee7000 shmid: 0x10000, shmaddr: 0x0, shmflg: 0x0
19816  client            SHMDT                0 shmaddr: 0x7f4fd8ee7000
19813  server            SHMDT                0 shmaddr: 0x7f1cf8b1f000
19813  server           SHMCTL                0 shmid: 0x10000, cmd: 0, buf: 0x0


Every call the shm* syscall (SHM column) is displayed
on separate line together with process info (PID/COMM
columns) and argument details: return value (RET column)
and syscall arguments (ARGs column).

The ARGs column contains 'arg: value' couples that represent
given syscall arguments as described in their manpage.

This works by tracing shm* system calls and sending
argument details to the python script.

A -T option can be used to include a timestamp column,
and a -n option to match on a command name. Regular
expressions are allowed.  For example, matching commands
containing "server" with timestamps:

# ./shmsnoop.py -T -n server
TIME(s)       PID    COMM                SYS              RET ARGs
0.563194000   19825  server            SHMDT                0 shmaddr: 0x7f74362e4000
0.563237000   19825  server           SHMCTL                0 shmid: 0x18000, cmd: 0, buf: 0x0


A -p option can be used to trace only selected process:

# ./shmsnoop.py -p 19855
PID    COMM                SYS              RET ARGs
19855  server            SHMDT                0 shmaddr: 0x7f4329ff8000
19855  server           SHMCTL                0 shmid: 0x20000, cmd: 0, buf: 0x0

USAGE message:
# ./shmsnoop.py -h
usage: shmsnoop.py [-h] [-T] [-p PID] [-t TID] [-d DURATION] [-n NAME]

Trace shm*() syscalls

optional arguments:
  -h, --help            show this help message and exit
  -T, --timestamp       include timestamp on output
  -p PID, --pid PID     trace this PID only
  -t TID, --tid TID     trace this TID only
  -d DURATION, --duration DURATION
                        total duration of trace in seconds
  -n NAME, --name NAME  only print process names containing this name

examples:
    ./shmsnoop           # trace all shm*() syscalls
    ./shmsnoop -T        # include timestamps
    ./shmsnoop -p 181    # only trace PID 181
    ./shmsnoop -t 123    # only trace TID 123
    ./shmsnoop -d 10     # trace for 10 seconds only
    ./shmsnoop -n main   # only print process names containing "main"