Re: [PATCH 2/4] samples/bpf: Use llc in PATH, rather than a hardcoded value

[Daniel Borkmann]

On 03/31/2016 07:46 PM, Alexei Starovoitov wrote:
> On 3/31/16 4:25 AM, Naveen N. Rao wrote:
> > While at it, fix some typos in the comment.
> >
> > Cc: Alexei Starovoitov <ast@xxxxxx>
> > Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> > Cc: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxx>
> > Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> > Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> > ---
> >   samples/bpf/Makefile | 11 ++++-------
> >   1 file changed, 4 insertions(+), 7 deletions(-)
> >
> > diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> > index 502c9fc..88bc5a0 100644
> > --- a/samples/bpf/Makefile
> > +++ b/samples/bpf/Makefile
> > @@ -76,16 +76,13 @@ HOSTLOADLIBES_offwaketime += -lelf
> >   HOSTLOADLIBES_spintest += -lelf
> >   HOSTLOADLIBES_map_perf_test += -lelf -lrt
> >
> > -# point this to your LLVM backend with bpf support
> > -LLC=$(srctree)/tools/bpf/llvm/bld/Debug+Asserts/bin/llc
> > -
> > -# asm/sysreg.h inline assmbly used by it is incompatible with llvm.
> > -# But, ehere is not easy way to fix it, so just exclude it since it is
> > +# asm/sysreg.h - inline assembly used by it is incompatible with llvm.
> > +# But, there is no easy way to fix it, so just exclude it since it is
> >   # useless for BPF samples.
> >   $(obj)/%.o: $(src)/%.c
> >       clang $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(EXTRA_CFLAGS) \
> >           -D__KERNEL__ -D__ASM_SYSREG_H -Wno-unused-value -Wno-pointer-sign \
> > -        -O2 -emit-llvm -c $< -o -| $(LLC) -march=bpf -filetype=obj -o $@
> > +        -O2 -emit-llvm -c $< -o -| llc -march=bpf -filetype=obj -o $@
> >       clang $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(EXTRA_CFLAGS) \
> >           -D__KERNEL__ -D__ASM_SYSREG_H -Wno-unused-value -Wno-pointer-sign \
> > -        -O2 -emit-llvm -c $< -o -| $(LLC) -march=bpf -filetype=asm -o $@.s
> > +        -O2 -emit-llvm -c $< -o -| llc -march=bpf -filetype=asm -o $@.s
>
> that was a workaround when clang/llvm didn't have bpf support.
> Now clang 3.7 and 3.8 have bpf built-in, so make sense to remove
> manual calls to llc completely.
> Just use 'clang -target bpf -O2 -D... -c $< -o $@'

+1, the clang part in that Makefile should also more correctly be called
with '-target bpf' as it turns out (despite llc with '-march=bpf' ...).
Better to use clang directly as suggested by Alexei.