perf jvmti: unconditionally links against -lelf

perf jvmti: unconditionally links against -lelf

[Alexey Brodkin]

Hi Jiri,

Just tried to cross-compile perf with pretty bare-minimal toolchain
which has no libelf installed for the target (for the record I used
SNPS ARC pre-built arc-2016.09 tools) like that:
--------------->8------------
make NO_LIBELF=1
--------------->8------------

And got the following build failure:
--------------->8------------
? LINK?????libperf-jvmti.so
.../2016.09-uclibc-archs/bin/../lib/gcc/arc-snps-linux-uclibc/6.2.1/../../../../arc-snps-linux-uclibc/bin/ld: cannot find -lelf
--------------->8------------

First I was surprised because I intentionally disabled usage of libelf
but after some grepping figured out jvmti is linked against libelf
regardless any settings, see:
--------------->8------------
$(OUTPUT)$(LIBJVMTI): $(LIBJVMTI_IN)
? ? ? ?$(QUIET_LINK)$(CC) -shared -Wl,-soname -Wl,$(LIBJVMTI) -o $@ $< -lelf -lrt
endif
--------------->8------------

This comes from commit?d4dfdf00d43e ("perf jvmti: Plug compilation into perf build").

I'm not really sure what could be the best solution to the problem I see.
If libelf is a real must for jvmti then probably we may force set?NO_JVMTI=1
if?NO_LIBELF=1 is passed on the command line.

At least the following builds perf for me without issues:
--------------->8------------
make NO_LIBELF=1 NO_JVMTI=1
--------------->8------------

Regards,
Alexey

perf jvmti: unconditionally links against -lelf

[Jiri Olsa]

On Wed, Apr 12, 2017@09:58:26AM +0000, Alexey Brodkin wrote:
> Hi Jiri,
> 
> Just tried to cross-compile perf with pretty bare-minimal toolchain
> which has no libelf installed for the target (for the record I used
> SNPS ARC pre-built arc-2016.09 tools) like that:
> --------------->8------------
> make NO_LIBELF=1
> --------------->8------------
> 
> And got the following build failure:
> --------------->8------------
> ? LINK?????libperf-jvmti.so
> .../2016.09-uclibc-archs/bin/../lib/gcc/arc-snps-linux-uclibc/6.2.1/../../../../arc-snps-linux-uclibc/bin/ld: cannot find -lelf
> --------------->8------------
> 
> First I was surprised because I intentionally disabled usage of libelf
> but after some grepping figured out jvmti is linked against libelf
> regardless any settings, see:
> --------------->8------------
> $(OUTPUT)$(LIBJVMTI): $(LIBJVMTI_IN)
> ? ? ? ?$(QUIET_LINK)$(CC) -shared -Wl,-soname -Wl,$(LIBJVMTI) -o $@ $< -lelf -lrt
> endif
> --------------->8------------
> 
> This comes from commit?d4dfdf00d43e ("perf jvmti: Plug compilation into perf build").
> 
> I'm not really sure what could be the best solution to the problem I see.
> If libelf is a real must for jvmti then probably we may force set?NO_JVMTI=1
> if?NO_LIBELF=1 is passed on the command line.
> 
> At least the following builds perf for me without issues:
> --------------->8------------
> make NO_LIBELF=1 NO_JVMTI=1
> --------------->8------------

hi,
incidently, David just posted patch for this ;-)
  http://marc.info/?l=linux-kernel&m=149197980107421&w=2

should be merged soon

jirka

perf jvmti: unconditionally links against -lelf

[Alexey Brodkin]

Hi Jiri,

On Wed, 2017-04-12@12:19 +0200, Jiri Olsa wrote:
> On Wed, Apr 12, 2017@09:58:26AM +0000, Alexey Brodkin wrote:
> > 
> > Hi Jiri,
> > 
> > Just tried to cross-compile perf with pretty bare-minimal toolchain
> > which has no libelf installed for the target (for the record I used
> > SNPS ARC pre-built arc-2016.09 tools) like that:
> > --------------->8------------
> > make NO_LIBELF=1
> > --------------->8------------
> > 
> > And got the following build failure:
> > --------------->8------------
> > ? LINK?????libperf-jvmti.so
> > .../2016.09-uclibc-archs/bin/../lib/gcc/arc-snps-linux-uclibc/6.2.1/../../../../arc-snps-linux-uclibc/bin/ld: cannot find -lelf
> > --------------->8------------
> > 
> > First I was surprised because I intentionally disabled usage of libelf
> > but after some grepping figured out jvmti is linked against libelf
> > regardless any settings, see:
> > --------------->8------------
> > $(OUTPUT)$(LIBJVMTI): $(LIBJVMTI_IN)
> > ? ? ? ?$(QUIET_LINK)$(CC) -shared -Wl,-soname -Wl,$(LIBJVMTI) -o $@ $< -lelf -lrt
> > endif
> > --------------->8------------
> > 
> > This comes from commit?d4dfdf00d43e ("perf jvmti: Plug compilation into perf build").
> > 
> > I'm not really sure what could be the best solution to the problem I see.
> > If libelf is a real must for jvmti then probably we may force set?NO_JVMTI=1
> > if?NO_LIBELF=1 is passed on the command line.
> > 
> > At least the following builds perf for me without issues:
> > --------------->8------------
> > make NO_LIBELF=1 NO_JVMTI=1
> > --------------->8------------
> 
> hi,
> incidently, David just posted patch for this ;-)

So good to know somebody has already fixed my problem :)
Thanks for letting me know!

-Alexey