linux-kernel - [PATCH 6/8] tools lib bpf: Use FEATURE_USER to allow building in the same dir as perf

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Message-Id: <1442870601-26004-7-git-send-email-acme@kernel.org>
Date:	Mon, 21 Sep 2015 18:23:19 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Jiri Olsa <jolsa@...nel.org>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Borislav Petkov <bp@...e.de>, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Wang Nan <wangnan0@...wei.com>, pi3orama@....com
Subject: [PATCH 6/8] tools lib bpf: Use FEATURE_USER to allow building in the same dir as perf

From: Arnaldo Carvalho de Melo <acme@...hat.com>

When building tools/lib/bpf as part of the tools/perf/ build process,
which will happend when we introduce a patch wiring that up, we end up
stomping on the feature detection caching mechanism, that uses a file in
the output directory (O=) that is shared by libbpf and perf to check if
something changed from one build to another that requires redoing the
feature detection process.

By using the recently introduced FEATURE_USER tools/build/ knob, we can
avoid that:

Before, every make invokation would run the feature detection:

  $ make O=/tmp/build/perf -C tools/perf
  make: Entering directory '/home/git/linux/tools/perf'
  Auto-detecting system features:
  ...                         dwarf: [ on  ]
  ...                         glibc: [ on  ]
  <SNIP>
  ...                     get_cpuid: [ on  ]
  ...                           bpf: [ on  ]

    GEN      perf-archive
    GEN      perf-with-kcore

  Auto-detecting system features:
  ...                        libelf: [ on  ]
  ...                           bpf: [ on  ]
  <SNIP>

After:

  $ make O=/tmp/build/perf -C tools/perf
  make: Entering directory '/home/git/linux/tools/perf'
    BUILD:   Doing 'make -j4' parallel build
  make: Leaving directory '/home/git/linux/tools/perf'
  $

Because we now have two different feature detection state files:

  $ ls -la /tmp/build/perf/FEATURE-DUMP*
  -rw-rw-r--. 1 acme acme 338 Sep 21 17:25 /tmp/build/perf/FEATURE-DUMP
  -rw-rw-r--. 1 acme acme  33 Sep 21 17:25 /tmp/build/perf/FEATURE-DUMP.libbpf
  $

Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Alexei Starovoitov <ast@...mgrid.com>
Cc: Borislav Petkov <bp@...e.de>
Cc: David Ahern <dsahern@...il.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Stephane Eranian <eranian@...gle.com>
Cc: Wang Nan <wangnan0@...wei.com>
Cc: pi3orama@....com
Fixes: 1b76c13e4b36 ("bpf tools: Introduce 'bpf' library and add bpf feature check")
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/lib/bpf/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index 604c12081b4b..e630f9fc4fb6 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -64,6 +64,7 @@ srctree := $(patsubst %/,%,$(dir $(srctree)))
 #$(info Determined 'srctree' to be $(srctree))
 endif
 
+FEATURE_USER = .libbpf
 FEATURE_TESTS = libelf libelf-getphdrnum libelf-mmap bpf
 FEATURE_DISPLAY = libelf bpf
 
-- 
2.1.0

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