Re: [PATCH bpf-next] libbpf: stop using feature-detection Makefiles

On 2/3/21 12:34 PM, Andrii Nakryiko wrote:

Libbpf's Makefile relies on Linux tools infrastructure's feature detection
framework, but libbpf's needs are very modest: it detects the presence of
libelf and libz, both of which are mandatory. So it doesn't benefit much from
the framework, but pays significant costs in terms of maintainability and
debugging experience, when something goes wrong. The other feature detector,
testing for the presernce of minimal BPF API in system headers is long
obsolete as well, providing no value.

So stop using feature detection and just assume the presence of libelf and
libz during build time. Worst case, user will get a clear and actionable
linker error, e.g.:

  /usr/bin/ld: cannot find -lelf

On the other hand, we completely bypass recurring issues various users
reported over time with false negatives of feature detection (libelf or libz
not being detected, while they are actually present in the system).

Cc: Arnaldo Carvalho de Melo <redacted>
Cc: Randy Dunlap <redacted>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/.gitignore |  1 -
 tools/lib/bpf/Makefile   | 47 ++++------------------------------------
 2 files changed, 4 insertions(+), 44 deletions(-)

Hi Andrii,

This does indeed fix the build problems that I was seeing,
so I can add:
Acked-by: Randy Dunlap <redacted>

but in the long term I think that features/libs/etc. that are
used should be checked for instead of being used blindly... IMO.

Thanks.

-- 
~Randy