Add uprobe strlen histogram example

This example traces all calls to libc's strlen(). The program is attached as a
retprobe, therefore giving access to the resulting string length. The value is
kept in a log2 histogram that is printed to console once per second.

Example:
```
$ sudo ./strlen_hist.py
22:12:51
     strlen return:      : count     distribution
         0 -> 1          : 2041     |****************                        |
         2 -> 3          : 1120     |********                                |
         4 -> 7          : 3300     |**************************              |
         8 -> 15         : 4995     |****************************************|
        16 -> 31         : 2130     |*****************                       |
        32 -> 63         : 562      |****                                    |
^C
```
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

Uprobe support

Use the full path invocation of objdump in both places.

Add a docstring for the variants of attach_retprobe.
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

The calculation of function address in non-shared libraries was
incorrect. Fix it.
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

This adds a similar set of functions to kprobes for userspace probes.
The calling convention is different, however, since the user must
provide a library/binary name and function symbol or address. Add two
simple test cases for both.

I don't see an easy way in this api to add auto-loading support, as in
kprobe functions that start with "kprobe__". Such niceties can come
later.
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

The base calling convention for uprobes is the same as kprobes, but just
the path in debug/tracing/ is slightly different. Add a new API for this
and slightly refactor the code.
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

wakeuptime

Add decode() to ascii string in offcputime.py

Fixes: #318
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

Updates to use cmake GLOB and libbcc.so.0 in python init

In order not to miss some files in the tools and examples source
directories, use cmake file(GLOB) to collect relevant files. To ease the
implementation, move all tools to be .py suffixed in the source, but
sans-suffix in the installation (same as before)

In addition, to prevent future API breakage confusion (though of course
that may still happen), use CDLL("libbcc.so.0") in the bcc __init__.py.

Fixes: #317
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

offcputime improvements

stack walker typo and improvement

Close fd and unshare when public map is destructed

Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

stack walking scripts

fix pep8 lint errors in the rest of the tools

no functional changes
Signed-off-by: Alexei Starovoitov <ast@fb.com>

fix pep8 lint errors in biolatency and biosnoop

Signed-off-by: Alexei Starovoitov <ast@fb.com>

Add ability to export maps, enables cross-program sharing

Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

Allow a program to export a map for other programs to use. This enables
cross-program map sharing.

parent program syntax:
BPF_TABLE("array", int, int, shared, 10);
BPF_TABLE_EXPORT(shared);

child program syntax:
BPF_TABLE("extern", int, int, shared, 10);
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

Add ability to set custom cflags when loading programs

Example:
b = bcc.BPF("myprog.c", cflags=["-DMYCUSTOMFLAG1", ...])
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

Remove runtime dependency on gcc stdarg headers and make

Remove the runtime dependency on gcc's stdarg.h. Do this by packaging
the (non-GPL) version shipped with clang. This allows the bulk of
kbuild_helper to be removed, at the expense of hardcoding the kernel
include paths. If in the future the kernel make system changes again to
require different -I paths, we'll have to think this through again.
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

add new Arch packages, new TOC and spiffy up the formatting