augmented_raw_syscalls.c defines the bpf map 'syscalls' which is
initialized by perf tool in user space to indicate which system calls
are enabled for tracing, on the other flip eBPF program relies on the
map to filter out the trace events which are not enabled.

The map also includes a field 'string_args_len[6]' which presents the
string length if the corresponding argument is a string type.

Now the map 'syscalls' is not used, bpf program doesn't use it as filter
anymore, this is replaced by using the function bpf_tail_call() and
PROG_ARRAY syscalls map.  And we don't need to explicitly set the string
length anymore, bpf_probe_read_str() is smart to copy the string and
return string length.

Therefore, it's safe to remove the bpf map 'syscalls'.

To consolidate the code, this patch removes the definition of map
'syscalls' from augmented_raw_syscalls.c and drops code for using
the map in the perf trace.

Note, since function trace__set_ev_qualifier_bpf_filter() is removed,
calling trace__init_syscall_bpf_progs() from it is also removed.  We
don't need to worry it because trace__init_syscall_bpf_progs() is
still invoked from trace__init_syscalls_bpf_prog_array_maps() for
initialization the system call's bpf program callback.

After:

  # perf trace -e examples/bpf/augmented_raw_syscalls.c,open* --max-events 10 perf stat --quiet sleep 0.001
  openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libm.so.6", O_RDONLY|O_CLOEXEC) = 3
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libelf.so.1", O_RDONLY|O_CLOEXEC) = 3
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libdw.so.1", O_RDONLY|O_CLOEXEC) = 3
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libunwind.so.8", O_RDONLY|O_CLOEXEC) = 3
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libunwind-aarch64.so.8", O_RDONLY|O_CLOEXEC) = 3
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libcrypto.so.3", O_RDONLY|O_CLOEXEC) = 3
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libslang.so.2", O_RDONLY|O_CLOEXEC) = 3
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libperl.so.5.34", O_RDONLY|O_CLOEXEC) = 3
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3

  # perf trace -e examples/bpf/augmented_raw_syscalls.c --max-events 10 perf stat --quiet sleep 0.001
  ... [continued]: execve())             = 0
  brk(NULL)                               = 0xaaaab1d28000
  faccessat(-100, "/etc/ld.so.preload", 4) = -1 ENOENT (No such file or directory)
  openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
  close(3</usr/lib/aarch64-linux-gnu/libcrypto.so.3>) = 0
  openat(AT_FDCWD, "/lib/aarch64-linux-gnu/libm.so.6", O_RDONLY|O_CLOEXEC) = 3
  read(3</usr/lib/aarch64-linux-gnu/libcrypto.so.3>, 0xfffff33f70d0, 832) = 832
  munmap(0xffffb5519000, 28672)           = 0
  munmap(0xffffb55b7000, 32880)           = 0
  mprotect(0xffffb55a6000, 61440, PROT_NONE) = 0
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20221121075237.127706-6-leo.yan@linaro.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>