On 11/29/19 3:00 PM, Toke Høiland-Jørgensen wrote:

Daniel Borkmann [off-list ref] writes:

quoted

On 11/28/19 5:07 PM, Toke Høiland-Jørgensen wrote:

quoted

From: Jiri Olsa <jolsa@kernel.org>

[...]

quoted

quoted

   ifeq ($(srctree),)
   srctree := $(patsubst %/,%,$(dir $(CURDIR)))

@@ -63,6 +72,19 @@ RM ?= rm -f
   FEATURE_USER = .bpftool
   FEATURE_TESTS = libbfd disassembler-four-args reallocarray zlib
   FEATURE_DISPLAY = libbfd disassembler-four-args zlib
+ifdef LIBBPF_DYNAMIC
+  FEATURE_TESTS   += libbpf
+  FEATURE_DISPLAY += libbpf
+
+  # for linking with debug library run:
+  # make LIBBPF_DYNAMIC=1 LIBBPF_DIR=/opt/libbpf

The Makefile already has BPF_DIR which points right now to
'$(srctree)/tools/lib/bpf/' and LIBBPF_PATH for the final one and
where $(LIBBPF_PATH)libbpf.a is expected to reside. Can't we improve
the Makefile to reuse and work with these instead of adding yet
another LIBBPF_DIR var which makes future changes in this area more
confusing? The libbpf build spills out libbpf.{a,so*} by default
anyway.

I see what you mean; however, LIBBPF_DIR is meant to be specifically an
override for the dynamic library, not just the path to libbpf.

Would it be less confusing to overload the LIBBPF_DYNAMIC variable
instead? I.e.,

make LIBBPF_DYNAMIC=1

would dynamically link against the libbpf installed in the system, but

make LIBBPF_DYNAMIC=/opt/libbpf

would override that and link against whatever is in /opt/libbpf instead?
WDYT?

Hm, given perf tool has similar LIB*_DIR vars in place for its libs, it probably
makes sense to stick with this convention as well then. Perhaps better in this
case to just rename s/BPF_DIR/BPF_SRC_DIR/, s/LIBBPF_OUTPUT/LIBBPF_BUILD_OUTPUT/,
and s/LIBBPF_PATH/LIBBPF_BUILD_PATH/ to make their purpose more clear.

One thing that would be good to do as well for this patch is to:

  i) Document both LIBBPF_DYNAMIC and LIBBPF_DIR in the Makefile comment you
     added at the top along with a simple usage example.

ii) Extend tools/testing/selftests/bpf/test_bpftool_build.sh with a dynamic
     linking test case, e.g. building libbpf into a temp dir and pointing
     LIBBPF_DIR to it for bpftool LIBBPF_DYNAMIC=1 build.

Thanks,
Daniel