perf bpf: Include uapi/linux/bpf.h from the 'perf trace' script's bpf.h

Commit-ID:  822c2621daadcf9e8fa8f11f7334e3c349434154
Gitweb:     https://git.kernel.org/tip/822c2621daadcf9e8fa8f11f7334e3c349434154
Author:     Arnaldo Carvalho de Melo <[email protected]>
AuthorDate: Wed, 1 Aug 2018 10:50:51 -0300
Committer:  Arnaldo Carvalho de Melo <[email protected]>
CommitDate: Wed, 1 Aug 2018 12:34:06 -0300

perf bpf: Include uapi/linux/bpf.h from the 'perf trace' script's bpf.h

The next example scripts need the definition for the BPF functions, i.e. things like BPF_FUNC_probe_read, and in time will require lots of other definitions found in uapi/linux/bpf.h, so include it from the bpf.h file included from the eBPF scripts build with clang via '-e bpf_script.c' like in this example:

  $ tail -8 tools/perf/examples/bpf/5sec.c
  #include <bpf.h>

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

  {
	return sec == 5;

}

  license(GPL);
  $

That 'bpf.h' include in the 5sec.c eBPF example will come from a set of header files crafted for building eBPF objects, that in a end-user system will come from:

/usr/lib/perf/include/bpf/bpf.h

And will include <uapi/linux/bpf.h> either from the place where the kernel was built, or from a kernel-devel rpm package like:

-working-directory /lib/modules/4.17.9-100.fc27.x86_64/build

That is set up by tools/perf/util/llvm-utils.c, and can be overriden by setting the 'kbuild-dir' variable in the "llvm" ~/.perfconfig file, like:

  # cat ~/.perfconfig
  [llvm]
       kbuild-dir = /home/foo/git/build/linux

This usually doesn't need any change, just documenting here my findings while working with this code.

In the future we may want to instead just use what is in /usr/include/linux/bpf.h, that comes from the UAPI provided from the kernel sources, for now, to avoid getting the kernel's non-UAPI "linux/bpf.h" file, that will cause clang to fail and is not what we want anyway (no BPF function definitions, etc), do it explicitely by asking for "uapi/linux/bpf.h".

---
 tools/perf/include/bpf/bpf.h | 3 +++
 1 file changed, 3 insertions(+)

index dd764ad5efdf..a63aa6241b7f 100644
@@ -1,6 +1,9 @@
 // SPDX-License-Identifier: GPL-2.0
 #ifndef _PERF_BPF_H
 #define _PERF_BPF_H
+
+#include <uapi/linux/bpf.h>
+
 #define SEC(NAME) __attribute__((section(NAME),  used))
 
 #define probe(function, vars) \