Em Mon, Dec 02, 2019 at 10:42:53AM -0800, Andrii Nakryiko escreveu: > On Mon, Dec 2, 2019 at 10:09 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: > > Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes: > > > On Wed, Nov 27, 2019 at 1:49 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote: > > >> adding support to link bpftool with libbpf dynamically, > > >> and config change for perf. > > >> It's now possible to use: > > >> $ make -C tools/bpf/bpftool/ LIBBPF_DYNAMIC=1 > > > I wonder what's the motivation behind these changes, though? Why is > > > linking bpftool dynamically with libbpf is necessary and important? > > > They are both developed tightly within kernel repo, so I fail to see > > > what are the huge advantages one can get from linking them > > > dynamically. > > Well, all the regular reasons for using dynamic linking (memory usage, > > binary size, etc). > bpftool is 327KB with statically linked libbpf. Hardly a huge problem > for either binary size or memory usage. CPU instruction cache usage is > also hardly a concern for bpftool specifically. > > But in particular, the ability to update the libbpf > > package if there's a serious bug, and have that be picked up by all > > utilities making use of it. > I agree, and that works only for utilities linking with libbpf > dynamically. For tools that build statically, you'd have to update > tools anyways. And if you can update libbpf, you can as well update > bpftool at the same time, so I don't think linking bpftool statically > with libbpf causes any new problems. > > No reason why bpftool should be special in that respect. > But I think bpftool is special and we actually want it to be special > and tightly coupled to libbpf with sometimes very intimate knowledge > of libbpf and access to "hidden" APIs. That allows us to experiment > with new stuff that requires use of bpftool (e.g., code generation for > BPF programs), without having to expose and seal public APIs. And I > don't think it's a problem from the point of code maintenance, because > both live in the same repository and are updated "atomically" when new > features are added or changed. > Beyond superficial binary size worries, I don't see any good reason > why we should add more complexity and variables to libbpf and bpftool > build processes just to have a "nice to have" option of linking > bpftool dynamically with libbpf. s/bpftool/perf/g s/libbpf/libperf/g And I would also agree 8-) - Arnaldo
