[net-next,V4,1/5] samples/bpf: add back functionality to redefine LLC command
diff mbox

Message ID 20160428122053.16807.93143.stgit@firesoul
State New
Headers show

Commit Message

Jesper Dangaard Brouer April 28, 2016, 12:20 p.m. UTC
It is practical to be-able-to redefine the location of the LLVM
command 'llc', because not all distros have a LLVM version with bpf
target support.  Thus, it is sometimes required to compile LLVM from
source, and sometimes it is not desired to overwrite the distros
default LLVM version.

This feature was removed with 128d1514be35 ("samples/bpf: Use llc in
PATH, rather than a hardcoded value").

Add this features back. Note that it is possible to redefine the LLC
on the make command like:

 make samples/bpf/ LLC=~/git/llvm/build/bin/llc

Fixes: 128d1514be35 ("samples/bpf: Use llc in PATH, rather than a hardcoded value")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
---
 samples/bpf/Makefile |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)


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Comments

Naveen N. Rao April 28, 2016, 1:21 p.m. UTC | #1
On 2016/04/28 02:20PM, Jesper Dangaard Brouer wrote:
> It is practical to be-able-to redefine the location of the LLVM
> command 'llc', because not all distros have a LLVM version with bpf
> target support.  Thus, it is sometimes required to compile LLVM from
> source, and sometimes it is not desired to overwrite the distros
> default LLVM version.
> 
> This feature was removed with 128d1514be35 ("samples/bpf: Use llc in
> PATH, rather than a hardcoded value").
> 
> Add this features back. Note that it is possible to redefine the LLC
> on the make command like:
> 
>  make samples/bpf/ LLC=~/git/llvm/build/bin/llc

I don't have an objection to this patch, but you didn't explain why/how 
this approach is better than just doing:
  PATH=~/git/llvm/build/bin make samples/bpf/

- Naveen

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Jesper Dangaard Brouer April 28, 2016, 2:40 p.m. UTC | #2
On Thu, 28 Apr 2016 18:51:33 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:

> > Add this features back. Note that it is possible to redefine the LLC
> > on the make command like:
> > 
> >  make samples/bpf/ LLC=~/git/llvm/build/bin/llc  
> 
> I don't have an objection to this patch, but you didn't explain why/how 
> this approach is better than just doing:
>   PATH=~/git/llvm/build/bin make samples/bpf/

It is almost the same. There is always another way to do the same.

I explicitly use this to test different combinations of LLC and CLANG,
in-order to validate Alexei's claim that older versions of CLANG could
still work with a newer version of LLC.  Thus, one use-case you
approach cannot cover ;-)

And clang seems to install a clang-3.9, which my solution also covers
by explicitly specifying CLANG=clang-3.9, if several avail clang's are
in the PATH.
Naveen N. Rao April 28, 2016, 2:50 p.m. UTC | #3
On 2016/04/28 04:40PM, Jesper Dangaard Brouer wrote:
> On Thu, 28 Apr 2016 18:51:33 +0530
> "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
> 
> > > Add this features back. Note that it is possible to redefine the LLC
> > > on the make command like:
> > > 
> > >  make samples/bpf/ LLC=~/git/llvm/build/bin/llc  
> > 
> > I don't have an objection to this patch, but you didn't explain why/how 
> > this approach is better than just doing:
> >   PATH=~/git/llvm/build/bin make samples/bpf/
> 
> It is almost the same. There is always another way to do the same.
> 
> I explicitly use this to test different combinations of LLC and CLANG,
> in-order to validate Alexei's claim that older versions of CLANG could
> still work with a newer version of LLC.  Thus, one use-case you
> approach cannot cover ;-)
> 
> And clang seems to install a clang-3.9, which my solution also covers
> by explicitly specifying CLANG=clang-3.9, if several avail clang's are
> in the PATH.

Ah, so a very niche use-case.

Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>

- Naveen

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Patch
diff mbox

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 744dd7a16144..5bae9536f100 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -81,10 +81,14 @@  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
+LLC ?= llc
+
 # 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 $@