Re: [PATCH bpf-next v5 9/9] selftest/bpf: Implement tests for bpftool gen min_core_btf

2022-01-28 18:23 UTC-0500 ~ Mauricio Vásquez Bernal [off-list ref]

On Fri, Jan 28, 2022 at 5:33 PM Mauricio Vásquez [off-list ref] wrote:

quoted

This commit implements some integration tests for "BTFGen". The goal
of such tests is to verify that the generated BTF file contains the
expected types.

This is not an exhaustive list of test cases. I'm not sure if this is
the approach we should follow to implement such tests, it seems to me
that checking each generated BTF file by hand is a lot of work but I
don't have other ideas to simplify it.

I considered different options to write these tests:
1. Use core_reloc_types.h to create a "source" BTF file with a lot of
types, then run BTFGen for all test_core_reloc_*.o files and use the
generated BTF file as btf_src_file in core_reloc.c. In other words,
re-run all test_core_reloc tests using a generated BTF file as source
instead of the "btf__core_reloc_" #name ".o" one. I think this test is
great because it tests the full functionality and actually checks that
the programs are able to run using the generated file. The problem is
how do we test that the BTFGen is creating an optimized file? Just
copying the source file without any modification will make all those
tests pass. We could check that the generated file is small (by
checking the size or the number of types) but it doesn't seem a very
reliable approach to me.

To check that the resulting BTF is optimised, one idea maybe would be to
first produce such a minimal BTF file for the program (with a manual
check) and then to expand it with additional symbols that you know are
all unnecessary to the program. Then for the test you can run bpftool to
produce the minimal BTF again and can check if any of the definitions
known as superfluous are still present.

Another solution could be to attempt to load the BTF and program by
removing any of the info from the produced BTF file, and see if the
program still loads.

Not sure if any of those solutions is easy to implement, though.

2. We could write some .c files with the types we expect to have on
the generated file and compare it with the generated file. The issue
here is that comparing those BTF files doesn't seem to be too
trivial...

Do you have any suggestions about it? Thanks!

I'm not familiar enough with BTF to have some great suggestion here,
maybe Andrii can help.

As a side note, it's already good to have some testing for the new
feature. The CI tests are pretty limited for bpftool at the moment and
we don't test much of it, so even basic tests to make sure that the
feature is not completely broken is a good start. Then the more we
cover, the safer we are of course :).

Thanks for this work!
Quentin