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Date: Sat, 30 Nov 2019 00:56:49 +0100 From: Daniel Borkmann <daniel@...earbox.net> To: Toke Høiland-Jørgensen <toke@...hat.com>, Alexei Starovoitov <alexei.starovoitov@...il.com> Cc: Jiri Olsa <jolsa@...nel.org>, lkml <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org, bpf@...r.kernel.org, Ingo Molnar <mingo@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Michael Petlan <mpetlan@...hat.com>, Jesper Dangaard Brouer <brouer@...hat.com>, Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>, Andrii Nakryiko <andriin@...com>, Arnaldo Carvalho de Melo <acme@...nel.org>, kubakici@...pl Subject: Re: [PATCH bpf v3] bpftool: Allow to link libbpf dynamically On 11/29/19 3:00 PM, Toke Høiland-Jørgensen wrote: > Daniel Borkmann <daniel@...earbox.net> writes: >> On 11/28/19 5:07 PM, Toke Høiland-Jørgensen wrote: >>> From: Jiri Olsa <jolsa@...nel.org> [...] >>> 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
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