Subject: Re: [net-next PATCH V2 5/5] samples/bpf: like LLC also verify and allow redefining CLANG command

From: Jesper Dangaard Brouer <[email-masked]>
Date: Wed, 27 Apr 2016 08:45:44 +0200

On Tue, 26 Apr 2016 10:36:10 -0700
Alexei Starovoitov <[email-masked]> wrote:

> On Tue, Apr 26, 2016 at 06:27:32PM +0200, Jesper Dangaard Brouer wrote:
> > Users are likely to manually compile both LLVM 'llc' and 'clang'
> > tools.  Thus, also allow redefining CLANG and verify command exist.
> > 
> > Makefile implementation wise, the target that verify the command have
> > been generalized.
> > 
> > Signed-off-by: Jesper Dangaard Brouer <[email-masked]>
> > ---
> >  samples/bpf/Makefile   |   23 +++++++++++++----------
> >  samples/bpf/README.rst |    6 +++---
> >  2 files changed, 16 insertions(+), 13 deletions(-)
> > 
> > diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> > index dd63521832d8..c02ea9d2a248 100644
> > --- a/samples/bpf/Makefile
> > +++ b/samples/bpf/Makefile
> > @@ -81,9 +81,10 @@ HOSTLOADLIBES_spintest += -lelf
> >  HOSTLOADLIBES_map_perf_test += -lelf -lrt
> >  HOSTLOADLIBES_test_overhead += -lelf -lrt
> >  
> > -# Allows pointing LLC to a LLVM backend with bpf support, redefine on cmdline:
> > -#  make samples/bpf/ LLC=~/git/llvm/build/bin/llc
> > +# Allows pointing LLC/CLANG to a LLVM backend with bpf support, redefine on cmdline:
> > +#  make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
> >  LLC ?= llc
> > +CLANG ?= clang
> >  
> >  # Trick to allow make to be run from this directory
> >  all:
> > @@ -94,15 +95,17 @@ clean:
> >  	@rm -f *~
> >  
> >  # Verify LLVM compiler is available and bpf target is supported
> > -.PHONY: verify_cmd_llc verify_target_bpf
> > +.PHONY: verify_cmd_llc verify_target_bpf $(CLANG) $(LLC)
> >  
> > -verify_cmd_llc:
> > -	@if ! (which "${LLC}" > /dev/null 2>&1); then \
> > -		echo "*** ERROR: Cannot find LLVM tool 'llc' (${LLC})" ;\
> > -		exit 1; \
> > -	else true; fi
> > +verify_cmds: $(CLANG) $(LLC)
> > +	@for TOOL in $^ ; do \
> > +		if ! (which "$${TOOL}" > /dev/null 2>&1); then \
> > +			echo "*** ERROR: Cannot find LLVM tool $${TOOL}" ;\
> > +			exit 1; \
> > +		else true; fi; \
> > +	done
> >  
> > -verify_target_bpf: verify_cmd_llc
> > +verify_target_bpf: verify_cmds
> >  	@if ! (${LLC} -march=bpf -mattr=help > /dev/null 2>&1); then \
> >  		echo "*** ERROR: LLVM (${LLC}) does not support 'bpf' target" ;\
> >  		echo "   NOTICE: LLVM version >= 3.7.1 required" ;\  
> 
> If I read the patch correctly, it only checks that any version
> of clang is available and llc supports -march=bpf.
> That's correct.

Yes, you read the patch correctly :-)

> There is no need to build the latest clang most of the time.
> clang 3.4 and 3.5 are fine to compile samples/bpf/
> since llvm ir is mostly compatible with llc from 3.7 or 3.8

Good to get confirmation. I was testing with clang 3.5.0, and llc 3.9-git.

> Acked-by: Alexei Starovoitov <[email-masked]>

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer