docs: update BPF features list (tracepoints to debug eBPF were removed)

Tracepoints for debugging eBPF were removed from the kernel (some other
mechanisms were being used instead, and they were not used often enough
to get proper maintenance). Let's specify this on the related line in
BPF features doc.

introduce {attach|detach}_raw_tracepoint API

Update docs/kernel_versions

Update list of main features and supported map types.

Also update list of architectures supporting JIT, and main features
list, with important upcoming changes (x86_32 for JIT, bpfilter and
AF_XDP for main features).

Also add notes on top of the lists about how to obtain the items of each
list.

Remove speculative map types with no link or schedule.

- Update links in doc (make them point from net-next to linux, when
  relevant).
- Add helpers bpf_xdp_adjust_tail() and bpf_skb_get_xfrm_state() to
  documentation and headers.
- Synchronise helpers with latest net-next.

The motivation comes from pull request #1689.
It attached a kprobe bpf program to kernel function
ttwu_do_wakeup for more accurate tracing.
Unfortunately, it broke runqlat.py in my
4.17 environment since ttwu_do_wakeup function
is inlined in my kernel with gcc 7.3.1.

4.17 introduced raw_tracepoint and this patch
added the relevant API to bcc. With this,
we can use tracepoints
sched:{sched_wakeup, sched_wakeup_new, sched_switch}
to measure runq latency more reliably.
Signed-off-by: Yonghong Song <yhs@fb.com>

Misc improvements to C++ API and example

introduce C++ get_syscall_fnname API

Support Cgroup Array in BCC

This fixed issue #1695 for C++. The example
HelloWorld.cc and tests test_libbcc also got fixed.
Signed-off-by: Yonghong Song <yhs@fb.com>

document cflags argument to BPF()

Refactor profile.py stack id error handling

using get_syscall_fnname to get kprobe func name for tools

Refactor offwaketime stack id error handling

introduce new BPF APIs to get kernel syscall entry func name/prefix

Fixed tools which are attached to syscall entry functions
"sys_*". Instead, use get_syscall_fnname to get
proper names.
Signed-off-by: Yonghong Song <yhs@fb.com>

As described in issue #1695, on 4.17 for syscalls on x86,
both sys_<fnname> and SyS_<fnname> are gone, the replacements
are __ia32_sys_sync and __x64_sys_sync.
The commit in Linus tree:
https://github.com/torvalds/linux/commit/d5a00528b58cdb2c71206e18bd021e34c4eab878

This patch introduced two APIs for python BPF object.
The API get_syscall_prefix() returns the prefix "sys_"/"__x64_sys_".
The API get_syscall_fnname(name) returns kernel function name for the syscall,
e.g., on x64, get_syscall_fnname("clone") will return "sys_clone" if kernel
has it, otherwise, "__x64_sys_clone".
get_syscall_prefix() is mostly useful for the regex func specifier of
attach_kprobe().

This patch only fixed the code using python API on examples and tests directory.

TOTO: python on tools directory, C++ and lua
Signed-off-by: Yonghong Song <yhs@fb.com>

print out more useful attach_kprobe failure information

As stated in issue #1695, the following commit
https://github.com/torvalds/linux/commit/5c8dad48e4f53d6fd0a7e4f95d7c1c983374de88
removed corresponding dmesg when attach_kprobe failed, and
userspace needs to print out proper error messages.
Signed-off-by: Yonghong Song <yhs@fb.com>

Add -c option for profile.py

Fix offwaketime PID / TGID handling

Refactor offcputime stack id error handling

Use better kprobes for runqlat.py

Fix probe name encoding in Python 3