On Sun, Dec 6, 2020 at 9:21 PM <saeed@xxxxxxxxxx> wrote: > > From: Saeed Mahameed <saeedm@xxxxxxxxxx> > > While playing with BTF for modules, i noticed that executing the command: > $ bpftool btf dump id <module's btf id> > > Fails due to lack of information in the BTF data. > > Maybe I am missing a step but actually adding the support for this is > very simple. yes, bpftool takes -B <path> argument for specifying base BTF. So if you added -B /sys/kernel/btf/vmlinux, it should have worked. I've added auto-detection logic for the case of `btf dump file /sys/kernel/btf/<module>` (see [0]), and we can also add it for when ID corresponds to a module BTF. But I think it's simplest to re-use the logic and just open /sys/kernel/btf/vmlinux, instead of adding narrowly-focused libbpf API for that. > > To completely parse modules BTF data, we need the vmlinux BTF as their > "base btf", which can be easily found by iterating through the btf ids and > looking for btf.name == "vmlinux". > > I am not sure why this hasn't been added by the original patchset because I never though of dumping module BTF by id, given there is nicely named /sys/kernel/btf/<module> :) > "Integrate kernel module BTF support", as adding the support for > this is very trivial. Unless i am missing something, CCing Andrii.. > > Signed-off-by: Saeed Mahameed <saeedm@xxxxxxxxxx> > CC: Andrii Nakryiko <andrii@xxxxxxxxxx> > --- > tools/lib/bpf/btf.c | 57 ++++++++++++++++++++++++++++++++++++++++ > tools/lib/bpf/btf.h | 2 ++ > tools/lib/bpf/libbpf.map | 1 + > 3 files changed, 60 insertions(+) > [...]
