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selftests/bpf: Pass all BPF .o's through BPF static linker 

Pass all individual BPF object files (generated from progs/*.c) through
`bpftool gen object` command to validate that BPF static linker doesn't
corrupt them.

As an additional sanity checks, validate that passing resulting object files
through linker again results in identical ELF files. Exact same ELF contents
can be guaranteed only after two passes, as after the first pass ELF sections
order changes, and thus .BTF.ext data sections order changes. That, in turn,
means that strings are added into the final BTF string sections in different
order, so .BTF strings data might not be exactly the same. But doing another
round of linking afterwards should result in the identical ELF file, which is
checked with additional `diff` command.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210318194036.3521577-12-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2021-03-18 12:40:35 -07:00 committed by Alexei Starovoitov
parent cab62c37be
commit 14137f3c62
1 changed files with 6 additions and 5 deletions
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11
tools/testing/selftests/bpf/Makefile
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@ -355,12 +355,13 @@ $(TRUNNER_BPF_OBJS): $(TRUNNER_OUTPUT)/%.o: \
$$(call $(TRUNNER_BPF_BUILD_RULE),$$<,$$@, \
$(TRUNNER_BPF_CFLAGS))
$(TRUNNER_BPF_SKELS): $(TRUNNER_OUTPUT)/%.skel.h: \
$(TRUNNER_OUTPUT)/%.o \
$(BPFTOOL) \
| $(TRUNNER_OUTPUT)
$(TRUNNER_BPF_SKELS): %.skel.h: %.o $(BPFTOOL) | $(TRUNNER_OUTPUT)
$$(call msg,GEN-SKEL,$(TRUNNER_BINARY),$$@)
$(Q)$$(BPFTOOL) gen skeleton $$< > $$@
$(Q)$$(BPFTOOL) gen object $$(<:.o=.linked.o) $$<
$(Q)$$(BPFTOOL) gen object $$(<:.o=.linked2.o) $$(<:.o=.linked.o)
$(Q)$$(BPFTOOL) gen object $$(<:.o=.linked3.o) $$(<:.o=.linked2.o)
$(Q)diff $$(<:.o=.linked2.o) $$(<:.o=.linked3.o)
$(Q)$$(BPFTOOL) gen skeleton $$(<:.o=.linked.o) name $$(notdir $$(<:.o=)) > $$@
endif
# ensure we set up tests.h header generation rule just once