Re: [PATCH v5 bpf-next 9/9] selftests/bpf: Add test for resolve_btfids

Andrii Nakryiko
2020-07-07T17:49:36Z

On Tue, Jul 7, 2020 at 8:57 AM Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Mon, Jul 06, 2020 at 06:26:28PM -0700, Andrii Nakryiko wrote:
> > On Fri, Jul 3, 2020 at 2:54 AM Jiri Olsa <jolsa@kernel.org> wrote:
> > >
> > > Adding resolve_btfids test under test_progs suite.
> > >
> > > It's possible to use btf_ids.h header and its logic in
> > > user space application, so we can add easy test for it.
> > >
> > > The test defines BTF_ID_LIST and checks it gets properly
> > > resolved.
> > >
> > > For this reason the test_progs binary (and other binaries
> > > that use TRUNNER* macros) is processed with resolve_btfids
> > > tool, which resolves BTF IDs in .BTF.ids section.
> > >
> > > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > > ---
> > > tools/testing/selftests/bpf/Makefile | 22 ++-
> > > .../selftests/bpf/prog_tests/resolve_btfids.c | 170 ++++++++++++++++++
> > > 2 files changed, 190 insertions(+), 2 deletions(-)
> > > create mode 100644 tools/testing/selftests/bpf/prog_tests/resolve_btfids.c
> > >
> > > diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> > > index 1f9c696b3edf..b47a685d12bd 100644
> > > --- a/tools/testing/selftests/bpf/Makefile
> > > +++ b/tools/testing/selftests/bpf/Makefile
> > > @@ -190,6 +190,16 @@ else
> > > cp "$(VMLINUX_H)" $@
> > > endif
> > >
> > > +$(SCRATCH_DIR)/resolve_btfids: $(BPFOBJ) \
> > > + $(TOOLSDIR)/bpf/resolve_btfids/main.c \
> > > + $(TOOLSDIR)/lib/rbtree.c \
> > > + $(TOOLSDIR)/lib/zalloc.c \
> > > + $(TOOLSDIR)/lib/string.c \
> > > + $(TOOLSDIR)/lib/ctype.c \
> > > + $(TOOLSDIR)/lib/str_error_r.c
> > > + $(Q)$(MAKE) $(submake_extras) -C $(TOOLSDIR)/bpf/resolve_btfids \
> > > + OUTPUT=$(SCRATCH_DIR)/ BPFOBJ=$(BPFOBJ)
> > > +
> >
> > please indent OUTPUT, so it doesn't look like it's a separate command
>
> ok
>
> >
> > > # Get Clang's default includes on this system, as opposed to those seen by
> > > # '-target bpf'. This fixes "missing" files on some architectures/distros,
> > > # such as asm/byteorder.h, asm/socket.h, asm/sockios.h, sys/cdefs.h etc.
> > > @@ -333,7 +343,8 @@ $(TRUNNER_TEST_OBJS): $(TRUNNER_OUTPUT)/%.test.o: \
> > > $(TRUNNER_BPF_SKELS) \
> > > $$(BPFOBJ) | $(TRUNNER_OUTPUT)
> > > $$(call msg,TEST-OBJ,$(TRUNNER_BINARY),$$@)
> > > - cd $$(@D) && $$(CC) -I. $$(CFLAGS) -c $(CURDIR)/$$< $$(LDLIBS) -o $$(@F)
> > > + cd $$(@D) && $$(CC) -I. $$(CFLAGS) $(TRUNNER_EXTRA_CFLAGS) \
> > > + -c $(CURDIR)/$$< $$(LDLIBS) -o $$(@F)
> > >
> > > $(TRUNNER_EXTRA_OBJS): $(TRUNNER_OUTPUT)/%.o: \
> > > %.c \
> > > @@ -355,6 +366,7 @@ $(OUTPUT)/$(TRUNNER_BINARY): $(TRUNNER_TEST_OBJS) \
> > > | $(TRUNNER_BINARY)-extras
> > > $$(call msg,BINARY,,$$@)
> > > $$(CC) $$(CFLAGS) $$(filter %.a %.o,$$^) $$(LDLIBS) -o $$@
> > > + $(TRUNNER_BINARY_EXTRA_CMD)
> >
> > no need to make this generic, just write out resolve_btfids here explicitly
>
> currently resolve_btfids fails if there's no .BTF.ids section found,
> but we can make it silently pass i nthis case and then we can invoke
> it for all the binaries

ah, I see. Yeah, either we can add an option to resolve_btfids to not
error when .BTF_ids is missing (probably best), or we can check
whether the test has .BTF_ids section, and if it does - run
resolve_btfids on it. Just ignoring errors always is more error-prone,
because we won't know if it's a real problem we are ignoring, or
missing .BTF_ids.

>
> >
> > >
> > > endef
> > >
> > > @@ -365,7 +377,10 @@ TRUNNER_EXTRA_SOURCES := test_progs.c cgroup_helpers.c trace_helpers.c \
> > > network_helpers.c testing_helpers.c \
> > > flow_dissector_load.h
> > > TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read \
> > > - $(wildcard progs/btf_dump_test_case_*.c)
> > > + $(wildcard progs/btf_dump_test_case_*.c) \
> > > + $(SCRATCH_DIR)/resolve_btfids
> > > +TRUNNER_EXTRA_CFLAGS := -D"BUILD_STR(s)=\#s" -DVMLINUX_BTF="BUILD_STR($(VMLINUX_BTF))"
> > > +TRUNNER_BINARY_EXTRA_CMD := $(SCRATCH_DIR)/resolve_btfids --btf $(VMLINUX_BTF) test_progs
> >
> > I hope we can get rid of this, see suggestion below.
> >
> > > TRUNNER_BPF_BUILD_RULE := CLANG_BPF_BUILD_RULE
> > > TRUNNER_BPF_CFLAGS := $(BPF_CFLAGS) $(CLANG_CFLAGS)
> > > TRUNNER_BPF_LDFLAGS := -mattr=+alu32
> > > @@ -373,6 +388,7 @@ $(eval $(call DEFINE_TEST_RUNNER,test_progs))
> > >
> >
> > [...]
> >
> > > +
> > > +static int duration;
> > > +
> > > +static struct btf *btf__parse_raw(const char *file)
> >
> > another copy here...
>
> ok
>
> >
> > > +{
> > > + struct btf *btf;
> > > + struct stat st;
> > > + __u8 *buf;
> > > + FILE *f;
> > > +
> >
> > [...]
> >
> > > +
> > > +BTF_ID_LIST(test_list)
> > > +BTF_ID_UNUSED
> > > +BTF_ID(typedef, pid_t)
> > > +BTF_ID(struct, sk_buff)
> > > +BTF_ID(union, thread_union)
> > > +BTF_ID(func, memcpy)
> > > +
> > > +struct symbol {
> > > + const char *name;
> > > + int type;
> > > + int id;
> > > +};
> > > +
> > > +struct symbol test_symbols[] = {
> > > + { "unused", -1, 0 },
> >
> > could use BTF_KIND_UNKN here instead of -1
>
> ok
>
> >
> > > + { "pid_t", BTF_KIND_TYPEDEF, -1 },
> > > + { "sk_buff", BTF_KIND_STRUCT, -1 },
> > > + { "thread_union", BTF_KIND_UNION, -1 },
> > > + { "memcpy", BTF_KIND_FUNC, -1 },
> > > +};
> > > +
> >
> > [...]
> >
> > > +
> > > +static int resolve_symbols(void)
> > > +{
> > > + const char *path = VMLINUX_BTF;
> >
> >
> > This build-time parameter passing to find the original VMLINUX_BTF
> > really sucks, IMO.
> >
> > Why not use the btf_dump tests approach and have our own small
> > "vmlinux BTF", which resolve_btfids would use to resolve these IDs?
> > See how btf_dump_xxx.c files define BTFs that are used in tests. You
> > can do something similar here, and use a well-known BPF object file as
> > a source of BTF, both here in a test and in Makefile for --btf param
> > to resolve_btfids?
>
> well VMLINUX_BTF is there and those types are used are not going
> away any time soon ;-) but yea, we can do that.. we do this also
> for bpftrace, it's nicer

"VMLINUX_BTF is there" is not really true in a lot of more complicated
setups, which is why I'd like to avoid that assumption. E.g., for
libbpf Travis CI, we build self-tests in one VM, but run the binary in
a different VM. So either vmlinux itself or the path to it might
change.

Also, having full control over **small** BTF allows to create various
test situations that might be harder to pinpoint in real vmlinux BTF,
e.g., same-named entities with different KINDS (typedef vs struct,
etc). Then if that fails, debugging this on a small BTF is much-much
easier than on a real thing. Real vmlinux BTF is being tested each
time you build a kernel and run selftests inside VM either way, so I
don't think we lose anything in terms of coverage.

>
> jirka
>