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.

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

fix profile.py with latest net-next

fixing bpflist

when you have lots of shortlived progs, there is posibillity of
race condition during proc scanning. you could get pid of this
shortlived prog, but when you will start to read it's fd/ dir
it will fail, as prog would be already terminated

The profile.py tries to validate whether the "ip" from the
context register is a kernel ip address or not by comparing
"ip" to the kernel PAGE_OFFSET.

On non-x86_64 architectures, PAGE_OFFSET can be directly used.
On x86_64 architecture, things become more complex.
With 4.17 (latest linus tree), __PAGE_OFFSET_BASE is gone
and replaced with __PAGE_OFFSET_BASE_L5 and __PAGE_OFFSET_BASE_L4
for 5 and 4 level page table respectively.
Running profile.py will have the following error:
    /virtual/main.c:41:18: error: use of undeclared identifier '__PAGE_OFFSET_BASE'
            if (ip > __PAGE_OFFSET_BASE) {
                     ^
    1 error generated.

So, for 4.17, __PAGE_OFFSET_BASE_{L4, L5} should be used.
For 4.16 and some old kernels (e.g., 4.11), which I did not
check earlier one, __PAGE_OFFSET_BASE should be used.
For even older kernels like 4.6, PAGE_OFFSET should be used.
Signed-off-by: Yonghong Song <yhs@fb.com>