Add support for listing struct/union/enum definitions using BTF

[mmisono]

'-l' option now can take struct/union/enum name and dump its definition
using BTF. For example:

% sudo ./src/bpftrace -l "enum bpf*"
enum bpf_access_type
enum bpf_adj_room_mode
enum bpf_arg_type
enum bpf_attach_type
enum bpf_cgroup_storage_type
[...]

and

% sudo ./src/bpftrace -lv "struct path"
BTF: using data from /sys/kernel/btf/vmlinux
struct path {
        struct vfsmount *mnt;
        struct dentry *dentry;
};

Checklist

• Language changes are updated in docs/reference_guide.md
• User-visible and non-trivial changes updated in CHANGELOG.md

[mmisono]

@olsajiri
I think the second commit c5959b6 is harmless, but could you take a look when you can?

[mmisono]

@danobi
Thanks for the review. I fixed the reviewed points. I also added 8aab8ab to list only usdt and uprobe when a pid is given. For example:

% sudo ./src/bpftrace -lv -p 25655
BTF: using data from /sys/kernel/btf/vmlinux
uprobe:/proc/25655/root/home/ubuntu/work/bpftrace/bpftrace/build-debug/a.out:__do_global_dtors_aux
uprobe:/proc/25655/root/home/ubuntu/work/bpftrace/bpftrace/build-debug/a.out:__libc_csu_fini
uprobe:/proc/25655/root/home/ubuntu/work/bpftrace/bpftrace/build-debug/a.out:__libc_csu_init
[...]
usdt:/proc/25655/root/lib/x86_64-linux-gnu/libc-2.27.so:libc:setjmp
usdt:/proc/25655/root/lib/x86_64-linux-gnu/libc-2.27.so:libc:longjmp
usdt:/proc/25655/root/lib/x86_64-linux-gnu/libc-2.27.so:libc:longjmp_target
[...]

Please let me know if this has a problem.

[danobi]

Can you add a "Changed" entry to the changelog for the usdt+uprobe change?

[danobi]

Please let me know if this has a problem.

Seems like a reasonable change

[mmisono]

• Updated changelog and fixed nits.