When compiling bpftool on a system where the /usr/include/asm symlink
doesn't exist (e.g. on an Ubuntu system without gcc-multilib installed),
the build fails with:

    CLANG    skeleton/profiler.bpf.o
  In file included from skeleton/profiler.bpf.c:4:
  In file included from /usr/include/linux/bpf.h:11:
  /usr/include/linux/types.h:5:10: fatal error: 'asm/types.h' file not found
  #include <asm/types.h>
           ^~~~~~~~~~~~~
  1 error generated.
  make: *** [Makefile:123: skeleton/profiler.bpf.o] Error 1

This indicates that the build is using linux/types.h from system headers
instead of source tree headers.

To fix this, adjust the clang search path to include the necessary
headers from tools/testing/selftests/bpf/include/uapi and
tools/include/uapi. Also use __bitwise__ instead of __bitwise in
skeleton/profiler.h to avoid clashing with the definition in
tools/testing/selftests/bpf/include/uapi/linux/types.h.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20200312130330.32239-1-tklauser@distanz.ch

With fentry/fexit programs, it is possible to profile BPF program with
hardware counters. Introduce bpftool "prog profile", which measures key
metrics of a BPF program.

bpftool prog profile command creates per-cpu perf events. Then it attaches
fentry/fexit programs to the target BPF program. The fentry program saves
perf event value to a map. The fexit program reads the perf event again,
and calculates the difference, which is the instructions/cycles used by
the target program.

Example input and output:

  ./bpftool prog profile id 337 duration 3 cycles instructions llc_misses

        4228 run_cnt
     3403698 cycles                                              (84.08%)
     3525294 instructions   #  1.04 insn per cycle               (84.05%)
          13 llc_misses     #  3.69 LLC misses per million isns  (83.50%)

This command measures cycles and instructions for BPF program with id
337 for 3 seconds. The program has triggered 4228 times. The rest of the
output is similar to perf-stat. In this example, the counters were only
counting ~84% of the time because of time multiplexing of perf counters.

Note that, this approach measures cycles and instructions in very small
increments. So the fentry/fexit programs introduce noticeable errors to
the measurement results.

The fentry/fexit programs are generated with BPF skeletons. Therefore, we
build bpftool twice. The first time _bpftool is built without skeletons.
Then, _bpftool is used to generate the skeletons. The second time, bpftool
is built with skeletons.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Quentin Monnet <quentin@isovalent.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200309173218.2739965-2-songliubraving@fb.com