Implement matching btfhub files with uname, makes centos7 work \o/

This looks like a big scary diff but it isnt really, it just regenerates the table and docs.

The major change is being able to finally work on systems that don't have BPF and don't have BTF, like good'ol centos7.

In quark_btf_open_hub() we try to match what we get from uname(2) with an existing kernel in our pre-compiled btfhub database. The matching is a bit crude, but good enough to work on centos7 and hopefully every other system that falls into the same case.

We have a dumb score system that tries to match the characters from the beginning and the end of uname -r, like:

$ ./quark-btf -l 3.10.0-123.el7.x86_64 3.10.0-1062.4.3.el7.x86_64

This matches the characters 3.10.0-1 from the beginning, it then scores one point for every character matched. Then it does the same from the end of the string, matching 3.el7.x86_64, scoring more one point for every character.

We do this for every kernel in the database and choose the highest scoring one.

In order to get it all working nicely some refactoring was needed in quark-btf.c and btf.c:

Change the name we store for the kernel in quark_btf{}, keep the escaped name for the structure, otherwise we wouldn't match on uname(2).
Cleanup a bunch of crap related to btf_targets.
Refactor gen_c() to play ball with new naming scheme.
Make quark-btf(8) take the same path as the library instead of reaching trough libbpf directly.
Make sure we stash a NULL in every btfhub entry.
Cleanup printing of quark-btf(8).
Cleanup main of quark-btf(8).
Fix some wrong documentation flags in quark-btf(8).
Implement a -l option in quark-btf(8) to lookup a kernel entry given a string.

Testing on centos7, my VM has:

[haesbaert@centos7 ~]$ uname -r
3.10.0-123.el7.x86_64

We don't really have that, but it matches something close:

[haesbaert@centos7 ~]$ ./quark-btf -l $(uname -r)
3.10.0-1062.4.3.el7.x86_64

And it works \o/, there is some erroneous printing that has to be cleanup, but not in dis diff:

[haesbaert@centos7 ~]$ sudo ./quark-mon -ks
quark-mon: open: /sys/kernel/tracing: No such file or directory
libbpf: kernel BTF is missing at '/sys/kernel/btf/vmlinux', was
CONFIG_DEBUG_INFO_BTF enabled?
libbpf: failed to find valid kernel BTF
quark-mon: open: /sys/kernel/tracing: No such file or directory
quark-mon: open: /sys/kernel/tracing: No such file or directory
quark-mon: open: /sys/kernel/tracing: No such file or directory
quark-mon: open: /sys/kernel/tracing: No such file or directory
quark-mon: open: /sys/kernel/tracing: No such file or directory
quark-mon: open: /sys/kernel/tracing: No such file or directory
quark-mon: open: /sys/kernel/tracing: No such file or directory
quark-mon: open: /sys/kernel/tracing: No such file or directory
quark-mon: open: /sys/kernel/tracing: No such file or directory
quark-mon: open: /sys/kernel/tracing: No such file or directory
quark-mon: open: /sys/kernel/tracing: No such file or directory
quark-mon: open: /sys/kernel/tracing: No such file or directory
quark-mon: open: /sys/kernel/tracing: No such file or directory
quark-mon: open: /sys/kernel/tracing: No such file or directory
->1068 (FORK+EXEC+EXIT+SETPROCTITLE)
  COMM  comm=echo
  CMDL  cmdline=[ /bin/echo, hi, from, centos7 ]
  PROC  ppid=1045
  PROC  uid=1000 gid=1000 suid=1000 sgid=1000 euid=1000 egid=1000 pgid=1068 sid=1045
  PROC  cap_inheritable=0x0 cap_permitted=0x0 cap_effective=0x0
  PROC  cap_bset=0xffffffffffffffff cap_ambient=0x0
  PROC  time_boot=1727420639000617449 tty_major=136 tty_minor=1
  PROC  entry_leader_type=UNKNOWN entry_leader=0
  CWD   cwd=/home/haesbaert
  FILE  filename=/bin/echo
  EXIT  exit_code=0 exit_time=1728038088089740243

elastic / quark

Implement matching btfhub files with uname, makes centos7 work \o/ #72