perf trace: Allow dumping a BPF map after setting up BPF events

Initial use case:

Dumping the maps setup by tools/perf/examples/bpf/augmented_raw_syscalls.c,
which so far are just booleans, showing just non-zeroed entries:

  # cat ~/.perfconfig
  [llvm]
	dump-obj = true
	clang-opt = -g
  [trace]
	#add_events = /home/acme/git/perf/tools/perf/examples/bpf/augmented_raw_syscalls.o
	add_events = /wb/augmented_raw_syscalls.o
  $ date
  Tue Feb 19 16:29:33 -03 2019
  $ ls -la /wb/augmented_raw_syscalls.o
  -rwxr-xr-x. 1 root root 14048 Jan 24 12:09 /wb/augmented_raw_syscalls.o
  $ file /wb/augmented_raw_syscalls.o
  /wb/augmented_raw_syscalls.o: ELF 64-bit LSB relocatable, eBPF, version 1 (SYSV), with debug_info, not stripped
  $
  # trace -e recvmmsg,sendmmsg --map-dump foobar
  ERROR: BPF map "foobar" not found
  # trace -e recvmmsg,sendmmsg --map-dump filtered_pids
  ERROR: BPF map "filtered_pids" not found
  # trace -e recvmmsg,sendmmsg --map-dump pids_filtered
  [2583] = 1,
  [2267] = 1,
  ^Z
  [1]+  Stopped                 trace -e recvmmsg,sendmmsg --map-dump pids_filtered
  # pidof trace
  2267
  # ps ax|grep gnome-terminal|grep -v grep
  2583 ?        Ssl   58:33 /usr/libexec/gnome-terminal-server
  ^C
  # trace -e recvmmsg,sendmmsg --map-dump syscalls
  [299] = 1,
  [307] = 1,
  ^C
  # grep x64_recvmmsg arch/x86/entry/syscalls/syscall_64.tbl
  299	64	recvmmsg		__x64_sys_recvmmsg
  # grep x64_sendmmsg arch/x86/entry/syscalls/syscall_64.tbl
  307	64	sendmmsg		__x64_sys_sendmmsg
  #

Next step probably will be something like 'perf stat's --interval-print and
--interval-clear.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Yonghong Song <yhs@fb.com>
Link: https://lkml.kernel.org/n/tip-ztxj25rtx37ixo9cfajt8ocy@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/tools/perf/Documentation/perf-trace.txt b/tools/perf/Documentation/perf-trace.txt
index 631e687be4eb..fc6e43262c41 100644
--- a/tools/perf/Documentation/perf-trace.txt
+++ b/tools/perf/Documentation/perf-trace.txt
@@ -210,6 +210,14 @@ the thread executes on the designated CPUs. Default is to monitor all CPUs.
 	may happen, for instance, when a thread gets migrated to a different CPU
 	while processing a syscall.
 
+--map-dump::
+	Dump BPF maps setup by events passed via -e, for instance the augmented_raw_syscalls
+	living in tools/perf/examples/bpf/augmented_raw_syscalls.c. For now this
+	dumps just boolean map values and integer keys, in time this will print in hex
+	by default and use BTF when available, as well as use functions to do pretty
+	printing using the existing 'perf trace' syscall arg beautifiers to map integer
+	arguments to strings (pid to comm, syscall id to syscall name, etc).
+
 
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