perf bpf: Add probe() helper to reduce kprobes boilerplate

So that kprobe definitions become:

  int probe(function, variables)(void *ctx, int err, var1, var2, ...)

The existing 5sec.c, got converted and goes from:

  SEC("func=hrtimer_nanosleep rqtp->tv_sec")
  int func(void *ctx, int err, long sec)
  {
  }

To:

  int probe(hrtimer_nanosleep, rqtp->tv_sec)(void *ctx, int err, long sec)
  {
  }

If we decide to add tv_nsec as well, then it becomes:

  $ cat tools/perf/examples/bpf/5sec.c
  #include <bpf.h>

  int probe(hrtimer_nanosleep, rqtp->tv_sec rqtp->tv_nsec)(void *ctx, int err, long sec, long nsec)
  {
	  return sec == 5;
  }

  license(GPL);
  $

And if we run it, system wide as before and run some 'sleep' with values
for the tv_nsec field, we get:

  # perf trace --no-syscalls -e tools/perf/examples/bpf/5sec.c
     0.000 perf_bpf_probe:hrtimer_nanosleep:(ffffffff9811b5f0) tv_sec=5 tv_nsec=100000000
  9641.650 perf_bpf_probe:hrtimer_nanosleep:(ffffffff9811b5f0) tv_sec=5 tv_nsec=123450001
  ^C#

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/n/tip-1v9r8f6ds5av0w9pcwpeknyl@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/examples/bpf/5sec.c

@@ -15,6 +15,13 @@
 
     . While this is running, run something like "sleep 5s".
 
+    . If we decide to add tv_nsec as well, then it becomes:
+
+      int probe(hrtimer_nanosleep, rqtp->tv_sec rqtp->tv_nsec)(void *ctx, int err, long sec, long nsec)
+
+      I.e. add where it comes from (rqtp->tv_nsec) and where it will be
+      accessible in the function body (nsec)
+
     # perf trace --no-syscalls -e tools/perf/examples/bpf/5sec.c/call-graph=dwarf/
          0.000 perf_bpf_probe:func:(ffffffff9811b5f0) tv_sec=5
                                            hrtimer_nanosleep ([kernel.kallsyms])
@@ -34,8 +41,7 @@
 
 #include <bpf.h>
 
-SEC("func=hrtimer_nanosleep rqtp->tv_sec")
-int func(void *ctx, int err, long sec)
+int probe(hrtimer_nanosleep, rqtp->tv_sec)(void *ctx, int err, long sec)
 {
 	return sec == 5;
 }

tools/perf/include/bpf/bpf.h

@@ -3,6 +3,9 @@
 #define _PERF_BPF_H
 #define SEC(NAME) __attribute__((section(NAME),  used))
 
+#define probe(function, vars) \
+	SEC(#function "=" #function " " #vars) function
+
 #define license(name) \
 char _license[] SEC("license") = #name; \
 int _version SEC("version") = LINUX_VERSION_CODE;