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

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

[Patrick Palka]

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@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Patrick Palka <patrick@parcs.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

Re: [PATCH] perf: Fix library detection when building without libelf

[Arnaldo Carvalho de Melo]

Em Wed, Oct 23, 2013 at 10:51:09PM -0400, Patrick Palka escreveu:
> 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.

Can you please check with the perf/core branch in my tree or Ingo's?

git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git perf/core

or Ingo's:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git perf/core

The feature detection was reworked and perhaps it is fixed there.

- Arnaldo

Re: [PATCH] perf: Fix library detection when building without libelf

[Patrick Palka]

On Thu, Oct 24, 2013 at 4:13 PM, Arnaldo Carvalho de Melo
<acme@ghostprotocols.net> wrote:
> Em Wed, Oct 23, 2013 at 10:51:09PM -0400, Patrick Palka escreveu:
>> 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.
>
> Can you please check with the perf/core branch in my tree or Ingo's?
>
> git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git perf/core
>
> or Ingo's:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git perf/core
>
> The feature detection was reworked and perhaps it is fixed there.
>
> - Arnaldo

I can't reproduce the detection failure in your branch, and a quick inspection
shows that the new feature-detection code is not subject to the kind of bug
that my patch fixed. So consider my patch obsolete.

Thanks,
Patrick

Re: [PATCH] perf: Fix library detection when building without libelf

[Arnaldo Carvalho de Melo]

Em Thu, Oct 24, 2013 at 04:36:47PM -0400, Patrick Palka escreveu:
> On Thu, Oct 24, 2013 at 4:13 PM, Arnaldo Carvalho de Melo
> > The feature detection was reworked and perhaps it is fixed there.
 
> I can't reproduce the detection failure in your branch, and a quick inspection
> shows that the new feature-detection code is not subject to the kind of bug
> that my patch fixed. So consider my patch obsolete.

Thanks for checking!

- Arnaldo