linux-kernel - [PATCH] perf: Fix library detection when building without libelf

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Date:	Wed, 23 Oct 2013 22:51:09 -0400
From:	Patrick Palka <patrick@...cs.ath.cx>
To:	linux-kernel@...r.kernel.org
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Jiri Olsa <jolsa@...hat.com>
Subject: [PATCH] perf: Fix library detection when building without libelf

When I attempt to build perf on a system with slang but without libelf,
'make' would wrongly complain that the slang library could not be found.

It turns out that this was happening because we are not filtering -lelf
from EXTLIBS early enough.  As a result, the library test for slang
(ditto for gtk, libaudit, etc) erroneously passes -lelf to try-cc, which
of course fails on a system without libelf.

This patch makes the filtering of -lelf from EXTLIBS occur right after
testing for libelf support, so that the subsequent library tests will
not erroneously pass -lelf to try-cc when building without libelf
support.

Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc: Jiri Olsa <jolsa@...hat.com>
Signed-off-by: Patrick Palka <patrick@...cs.ath.cx>
---
 tools/perf/Makefile        | 2 --
 tools/perf/config/Makefile | 4 ++++
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/perf/Makefile b/tools/perf/Makefile
index 64c043b..94635c8 100644
--- a/tools/perf/Makefile
+++ b/tools/perf/Makefile
@@ -443,8 +443,6 @@ ifneq ($(OUTPUT),)
 endif
 
 ifdef NO_LIBELF
-EXTLIBS := $(filter-out -lelf,$(EXTLIBS))
-
 # Remove ELF/DWARF dependent codes
 LIB_OBJS := $(filter-out $(OUTPUT)util/symbol-elf.o,$(LIB_OBJS))
 LIB_OBJS := $(filter-out $(OUTPUT)util/dwarf-aux.o,$(LIB_OBJS))
diff --git a/tools/perf/config/Makefile b/tools/perf/config/Makefile
index 5f6f9b3..1748767 100644
--- a/tools/perf/config/Makefile
+++ b/tools/perf/config/Makefile
@@ -174,6 +174,10 @@ else
 endif # SOURCE_LIBELF
 endif # NO_LIBELF
 
+ifdef NO_LIBELF
+EXTLIBS := $(filter-out -lelf,$(EXTLIBS))
+endif
+
 ifndef NO_LIBELF
 CFLAGS += -DLIBELF_SUPPORT
 FLAGS_LIBELF=$(CFLAGS) $(LDFLAGS) $(EXTLIBS)
-- 
1.8.4.rc3

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