Fix issue #1802.

On x64, the following commit (in 4.17) changed the raw parameter passed to
the syscall entry function from a list of parameters supplied in user space
to a single `pt_regs *` parameter. Also in 4.17, x64 syscall entry function
is changed from `sys_<name>` to `__x64_sys_<name>`.

```
commit fa697140f9a20119a9ec8fd7460cc4314fbdaff3
Author: Dominik Brodowski <linux@dominikbrodowski.net>
Date:   Thu Apr 5 11:53:02 2018 +0200

    syscalls/x86: Use 'struct pt_regs' based syscall calling convention for 64-bit syscalls

    Let's make use of ARCH_HAS_SYSCALL_WRAPPER=y on pure 64-bit x86-64 systems:

    Each syscall defines a stub which takes struct pt_regs as its only
    argument. It decodes just those parameters it needs, e.g:

            asmlinkage long sys_xyzzy(const struct pt_regs *regs)
            {
                    return SyS_xyzzy(regs->di, regs->si, regs->dx);
            }

    This approach avoids leaking random user-provided register content down
    the call chain.

    ...
```

In bcc, we support kprobe function signatures in the bpf program.
The rewriter will automatically generate proper assignment to
these parameters. With the above function signature change, the
original method does not work any more.

This patch enhanced rewriter to generate two version codes guarded
with CONFIG_ARCH_HAS_SYSCALL_WRAPPER. But we need to identify
whether a function will be attached to syscall entry function
or not during prog load time at which time the program has not
attached to any event.

The prefix `kprobe__` is used for kprobe autoload, we can use
`kprobe____x64_sys_` as the prefix to identify x64 syscall entry
functions. To support other architecture or not-autoloading program,
the prefix `syscall__` is introduced to signal it is a syscall
entry function.

trace.py and other tools which uses kprobe syscall entry functions
are also modified with the new interface so that they can
work properly with 4.17.
Signed-off-by: Yonghong Song <yhs@fb.com>

20fb64cd stops the whole AST traversal if it meets a bpf_probe_read call.  I
think the original intent was to simply not rewrite the third argument, so this
commit fixes it by remembering the third argument on bpf_probe_read call
traversals and overriding TraverseStmt to skip the traversal of that argument
when we meet it later.

bcc uses some func prefixes for auto load purpose. These
func prefixes include "kprobe__", "tracepoint__" and
"raw_tracepoint__". Currently we also pass this
function name as the program name to the kernel.

The kernel can only accept 16 bytes so long program
name will be truncated. For example, with bps we will see
something like
     287- <raw_tracepoint>       0      2 Jun10/17:07  raw_tracepoint_
     290- tracepoint             0      4 Jun10/17:08  tracepoint__soc
     297- kprobe                 0      2 Jun10/17:09  kprobe__tcp_cle

Such long prefixes are unnecessarily taking the space
for the real function name. This patch removed such prefixes
before giving them to the kernel.
The result will like below:
     311- <raw_tracepoint>       0      2 Jun10/17:44  sched_switch
     321- tracepoint             0      4 Jun10/17:45  sock__inet_sock
     322- kprobe                 0      2 Jun10/17:45  tcp_cleanup_rbu
Signed-off-by: Yonghong Song <yhs@fb.com>

commit 95b3d8c8 fixed the dport filtering of the kprobes variant by
moving the network byte order to host byte order conversation before the
filtering. Before submitting the perf event the byte order of the dport
was again converted - this commit removes this double conversion.

[V2] Add two map types for bpf_redirect_map()

Smoke test for tcpdrop

adjust tracepoint field type based on size

add missing types in bps

Also add a simple example for DEVMAP based on xdp_drop_count.py

v2:
  Add an example for CPUMAP
Signed-off-by: Gary Lin <glin@suse.com>

Those two map types are necessary to support bpf_redirect_map() in XDP.

v2:
  Use ArrayBase as the base class of DevMap and CpuMap
Signed-off-by: Gary Lin <glin@suse.com>

Add missing program and map types in bps
Signed-off-by: Yonghong Song <yhs@fb.com>

Fix issue #1807

tracepoint may have a format like this:
(from syscalls/sys_enter_socket)
	field:unsigned short common_type;	offset:0;	size:2;	signed:0;
	field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
	field:unsigned char common_preempt_count;	offset:3;	size:1;	signed:0;
	field:int common_pid;	offset:4;	size:4;	signed:1;

	field:int __syscall_nr;	offset:8;	size:4;	signed:1;
	field:int family;	offset:16;	size:8;	signed:0;
	field:int type;	offset:24;	size:8;	signed:0;
	field:int protocol;	offset:32;	size:8;	signed:0;

Current rewriter generates:
    struct tracepoint__syscalls__sys_enter_socket {
	    u64 __do_not_use__;
	    int __syscall_nr;
	    int family;
	    int type;
	    int protocol;
    };

This is incorrect as in the above structure, offsets of
`family`/`type`/`procotol` becomingg 12/16/20.

This patch fixed the issue by adjusting field type based on its size.
The new structure:
    struct tracepoint__syscalls__sys_enter_socket {
	    u64 __do_not_use__;
	    int __syscall_nr;
	    s64 family;
	    s64 type;
	    s64 protocol;
    };
The offsets of all fields are correct now.
Signed-off-by: Yonghong Song <yhs@fb.com>

add tcpdrop tool

Feat/add stack frames to funcslower

profile: remove remnant from old version

The comment on the instrumentation of perf_event_open should have
been removed in commit 715f7e6e.

Signed-off-by: Gary Lin <glin@suse.com>

2. Not using BPF_F_REUSE_STACKID in funcslower stack traces
3. Combining an ifdef check

fix a memory leak for getline()

The memory allocated by getline() is not freed.
This may cause some tool like clang memory
leak sanitizer complain.
Signed-off-by: Yonghong Song <yhs@fb.com>

Fix typo

daelays -> delays

skip probe rewriter for bpf_probe_read()

bpf_probe_read() is often used to access pointees in bpf programs.
Recent rewriter has become smarter so a lot of bpf_probe_read()
can be replaced with simple pointer/member access.

In certain cases, bpf_probe_read() is still preferred though.
For example, kernel net/tcp.h defined TCP_SKB_CB as below
  #define TCP_SKB_CB(__skb)	((struct tcp_skb_cb *)&((__skb)->cb[0]))
User can use below to access tcp_gso_size of a skb data structure.
  TCP_SKB_CB(skb)->tcp_gso_size
The rewriter will fail as it attempts to rewrite (__skb)->cb[0].

Instead of chasing down to prevent exactly the above pattern,
this patch detects function bpf_probe_read() in ProbeVisitor and
will skip it so bpf_probe_read()'s third parameter is a AddrOf.
This can also help other cases where rewriter is not
capable and user used bpf_probe_read() as the workaround.

Also fixed tcptop.py to use direct assignment instead of
bpf_probe_read. Otherwise, rewriter will actually rewrite
src address reference inside the bpf_probe_read().
Signed-off-by: Yonghong Song <yhs@fb.com>

Add "-D __BPF_TRACING__" to frontend compilation flags

In 4.17 kernel, x86 build requires compiler asm-goto support. clang
does not support asm-goto and bpf program compilation started to break.
The following kernel commit

  commit b1ae32dbab50ed19cfc16d225b0fb0114fb13025
  Author: Alexei Starovoitov <ast@kernel.org>
  Date:   Sun May 13 12:32:22 2018 -0700

      x86/cpufeature: Guard asm_volatile_goto usage for BPF compilation

      Workaround for the sake of BPF compilation which utilizes kernel
      headers, but clang does not support ASM GOTO and fails the build.

workarounded the issue by permitting native clang compilation.
A warning message, however, is issued:

  ./arch/x86/include/asm/cpufeature.h:150:2: warning: "Compiler lacks ASM_GOTO support.
        Add -D __BPF_TRACING__ to your compiler arguments" [-W#warnings]
  #warning "Compiler lacks ASM_GOTO support. Add -D __BPF_TRACING__ to your compil...
   ^
  1 warning generated.

This patch added "-D __BPF_TRACING__" to clang frontend compilation to
suppress the warning.
Signed-off-by: Yonghong Song <yhs@fb.com>

Refactor external pointer assignments

sync BPF compat headers with latest bpf-next, update BPF features list

Update doc/kernel-versions.md with latest eBPF features, map types,
JIT-compiler, helpers.

Synchronise headers with bpf-next (at commit bcece5dc40b9). Add
prototypes for the following helpers:

- bpf_get_stack()
- bpf_skb_load_bytes_relative()
- bpf_fib_lookup()
- bpf_sock_hash_update()
- bpf_msg_redirect_hash()
- bpf_sk_redirect_hash()
- bpf_lwt_push_encap()
- bpf_lwt_seg6_store_bytes()
- bpf_lwt_seg6_adjust_srh()
- bpf_lwt_seg6_action()
- bpf_rc_repeat()
- bpf_rc_keydown()

The code to track assignments of external pointers was scattered
between VisitVarDecl and VisitBinaryOperator.  This commit defines a
shared assignsExtPtr method.

Doing so also fixes a bug as VisitVarDecl was missing a case for
external pointers retrieved from maps.