On Mon, Nov 8, 2021 at 7:44 PM Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > On Sun, Nov 07, 2021 at 10:13:09PM -0800, Andrii Nakryiko wrote: > > Add test_progs-shared flavor to compile against libbpf as a shared > > library. This is useful to make sure that libbpf's backwards/forward > > compatibility guarantees are upheld. Currently this has to be checked > > locally, but in the future we'll automate at least some scenarios as > > part of libbpf CI runs. > > > > Biggest change is how either libbpf.a or libbpf.so is passed to the > > compiler, which is controled on per-flavor through a new TRUNNER_LIBBPF > > parameter. All the places that depend on libbpf artifacts (headers, > > library itself, etc) to be built are moved to order-only dependency on > > $(BPFOBJ). rpath is used to specify relative location to where libbpf.so > > should be so that when test_progs-shared is run under QEMU, libbpf.so is > > still going to be discovered correctly. > > > > Few selftests are using or testing internal libbpf APIs, so are not > > compatible with shared library use of libbpf. Filter them out for shared > > flavor. > ... > > +# Define test_progs-shared test runner. > > +TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE > > +TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS) -DENABLE_ATOMICS_TESTS > > +TRUNNER_EXTRA_CFLAGS := -Wl,-rpath=$(subst $(CURDIR)/,,$(dir $(BPFOBJ))) > > +TRUNNER_LIBBPF := $(patsubst %libbpf.a,%libbpf.so,$(BPFOBJ)) > > +TRUNNER_TESTS_BLACKLIST := cpu_mask.c hashmap.c perf_buffer.c raw_tp_test_run.c > > +$(eval $(call DEFINE_TEST_RUNNER,test_progs,shared)) > > +TRUNNER_TESTS_BLACKLIST := > > It's a good idea to add libbpf.so test, but going through test_progs is imo overkill. > No reason to run more than one test with shared lib. > If it links fine it's pretty much certain that it will work. > Maybe convert test_maps into shared only? CI runs it already. If some APIs are not used from a user app, their symbols won't be used during dynamic linking, so they won't be tested neither for linking nor functionally. E.g., in this case all the btf_dump__new(), btf__dedup(), etc, invocations won't be verified even at dynamic linking time. At least that's my understanding from looking at generated ELF binaries. And that was the sole motivator (at least initially) to add -shared flavor, so that I can make sure it works. Learned a bit about symbol versioning and symbol visibility from that, so definitely not a waste of time. But more broadly, what's the concern? User-space part compilation time for test_progs is extremely fast, it's the BPF object compilation that is slow. I'll send another Makefile change to eliminate the third compilation variant for BPF source code in the next few days (will roll it into this patch set unless it lands first), so that will go away. It seems useful to have a full-featured testing ground for libbpf.so, especially that I don't use (and thus don't test and validate constantly) it in practice in my own applications.
