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

From: Jiri Olsa <[email-masked]>
Date: Tue, 7 Jul 2020 17:57:20 +0200

On Mon, Jul 06, 2020 at 06:26:28PM -0700, Andrii Nakryiko wrote:
> On Fri, Jul 3, 2020 at 2:54 AM Jiri Olsa <[email-masked]> 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 <[email-masked]>
> > ---
> >  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

> 
> >
> >  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

jirka