`trace` filters and print expressions can now use the
magic STRCMP helper function to compare strings. The first
string must be a compile-time constant literal string,
such as "test", and the second string can be determined at
runtime (e.g., from a function argument). The codegen for
STRCMP is on a case-by-case basis for each literal string,
and it generates an inline function with a constant-length
loop that compares the string's characters. This is a
decent workaround until we get something more reasonable
from the kernel side, such as a `bpf_strcmp` helper.

Usage example:

```
trace 'p:c:open (STRCMP("test.txt", arg1)) "%s", arg1'
``

funccount: Generalized for uprobes, tracepoints, and USDT

As part of the funccount work, the kprobe quota test doesn't fail
early when adding multiple kprobes at once (with `event_re`), but
rather only when the 1000th probe is being added. Revert to the old
behavior, which fixes the `test_probe_quota` test. Add similar test
for uprobes, `test_uprobe_quota`, which tests the recently-added
uprobe regex support.

This commit updates `funccount` to support attaching to a set of
user functions, kernel tracepoints, or USDT probes using familiar
syntax. Along the way, the implementation has been updated to use
a separate BPF function for each target function, because using
the instruction pointer to determine the function name doesn't
work for anything other than kprobes. Even though the BPF program
can now be potentially larger, testing with 40-50 attach points
shows no significant overhead compared to the previous version.

Examples of what's now possible:

```
funccount t:block:*
funccount u:node:gc*
funccount -r 'c:(read|write)$'
funccount -p 142 u:ruby:object__create
```

Make the `get_user_functions`, `get_kprobe_functions`, and
`get_tracepoints` methods publicly accessible from the BPF class.
These can then be used by tools that need to do their own work
before attaching programs to a set of functions or tracepoints.

* argdist: linter cleanup

* cpudist: linter cleanup

* execsnoop: linter cleanup

* funclatency: linter cleanup

* gethostlatency: linter cleanup

* hardirqs: linter cleanup

* memleak: linter cleanup

* mountsnoop: linter cleanup

* offcputime: linter cleanup

* softirqs: linter cleanup

* solisten: linter cleanup and u+x mode

* stacksnoop: linter cleanup

* tplist: linter cleanup

* trace: linter cleanup

mysqld_slower: Fix breakage after USDT API change

* trace: Additional include files support

Similarly to `argdist`, `trace` now has a `-I` option for adding
include files that can be used in filter and print expressions.
This also required a slight modification to `argdist`'s syntax
for consistency: where previously we would allow `-I header1 header2`,
we now require `-I header1 -I header2` to avoid any mixups with
which argument is a header file and which is a probe for `trace`.

This is very unlikely to break anyone, because I haven't seen the
`-I` option used at all, not to mention extensively with multiple
headers.

Also made sure the man and example pages are up to date.

* argdist: Update -C and -H switches for consistency

This commit updates `argdist`'s `-H` and `-C` switches for consistency
with the `-I` switch and `trace`'s switches. Specifically, each probe
needs an explicit `-C` or `-H` specifier in front of it. This also
allows safe and understandable mixing of histogram and counting probes,
for example:

```
argdist -C 'p:c:write()' -H 'p::vfs__write(int fd, const void *buf, size_t size):size_t:size#write sizes'
```

* trace: Fix stack trace support for tracepoints

Tracepoint probes don't have a `ctx` argument, it's called `args`
instead. The recently-added stack trace support code didn't take
this into account, and consequently didn't work for tracepoints.
This commit fixes the issue, so we can now do things like
`trace -K t:block:block_rq_complete`.

Making selection of kernel headers type automatic

Modern versions of USDT probes (such as what's found in
PostgreSQL when compiled with `--enable-dtrace`) may have
the offset listed after the global symbol for USDT
arguments of the format `4@symbol+8(%rip)`. This commit
extends the argument parser to support these cases, adds
tests for these cases, and makes sure that in case of a
parse error, the parser always moves forward and consumes
at least one character. Presently, the parser would get
stuck on the problematic position and enter an infinite
loop.

Add vxlan gbp header

* Filter by process ID in ex4slower

* Updated the rest of the tools to filter by process ID

The BPF class constructor now accepts an array of USDT
contexts instead of just one object. Update the examples
in **examples/tracing** and docs in **docs** to reflect
this change.

A recent PR to the USDT infrastructure changed the BPF
module constructor to accept an array of USDT contexts.
This commit updates `mysqld_slower` to use that new
constructor.

Filesystem mounting and unmounting affects an entire system, so this is
a great candidate for system-wide tracing. mountsnoop.py watches all
mounts and unmounts and is also mount namespace-aware, which is a
requirement for working with containers.
Signed-off-by: Omar Sandoval <osandov@fb.com>

Signed-off-by: Deepa Kalani <dkalani@plumgrid.com>

The %K and %U format specifiers can be used in a trace
format string to resolve kernel and user symbols,
respectively. For example, the pthread_create USDT probe
has an argument pointing to the new thread's function.
To trace pthread_create and print the symbolic name of
the new thread's function, use:

```
trace 'u:pthread:pthread_create "%U", arg3'
```

The %U specifier resolves addresses in the event's process,
while the %K specifier resolves kernel addresses.

* Use real PID instead of TID in opensnoop

* Replaced -t for timestamp with -T

* Support TID as well as PID

* Update opensnoop example

* Update man

* Added missing documentation re -n option

* Minor: styling

Update INSTALL.md

Quickstart leaves out installing the examples.

GCC 6 behaves slightly differently when using -isystem, and our use of
that parameter is causing a build failure. Avoid using -isystem on
gcc6+ for now, until that compiler becomes a bit more mainstream and
we can debug further.

Failure had been introuced in d19e0cb0.
Signed-off-by: Marco Leogrande <marcol@plumgrid.com>

* bcc: Allow custom bucket formatting for histogram keys

When histogram keys are complex structures (`ct.Structure`
created from C struct), they can't be used as dictionary keys
for counting purposes without a custom hashing function.
Allow the user to provide such hashing function when calling
`print_log_hist` to print the histogram.

* bcc: Allow regular expression in attach_uretprobe

Similarly to `attach_uprobe`, `attach_uretprobe` now supports
taking a regular expression.

* funclatency: Support user functions

funclatency now supports user functions (including regular
expressions) in addition to kernel functions. When multiple
processes are traced, the output is always per-function, per-
process. When a single process is traced, the output can be
combined for all traced functions (as with kernel functions).

Usage examples:

```
funclatency pthread:*mutex* -p 6449 -F
funclatency c:read
funclatency dd:* -p $(pidof dd) -uF
```

FC23 and FC24 need Clang 3.9.0 because of ABI changes in the C++
runtime library. Split the installation instructions to FC22 and
FC23/24.

* cc: Add USDT location and argument reporting

libbcc now exposes USDT location and argument information using
two new APIs: `bcc_usdt_get_location` and `bcc_usdt_get_argument`.

* python: Retrieve USDT locations and arguments

Add wrappers in the libbcc.py file to access the new APIs for
retrieving USDT location and argument information. Also add
high-level classes in usdt.py to access this information and
format arguments and locations in a shape suitable for display.

* tplist: Print USDT locations and arguments

Add super-verbose mode (-vv) to tplist where it prints USDT locations
and arguments including full detail on registers, offsets, and global
identifier offsets.

this is initial commit of LuaJIT bytecode to BPF
compiler project that enables writing both kernel
and user-part of the code as Lua

* stackcount: Support user-space functions

Add support for user-space functions in `stackcount` by taking an additional
`-l` command-line parameter specifying the name of the user-space library.
When a user-space library is specified, `stackcount` attaches to a specific
process and traces a user-space function with user-space stacks only.
Regex support for uprobes (similar to what is available for kprobes) is
not currently provided.

Also add a couple of functions to the `BPF` object for consistency.

* bcc: Support regex in attach_uprobe

attach_kprobe allows a regular expression for the function name,
while attach_uprobe does not. Add support in libccc for enumerating
all the function symbols in a binary, and use that in the BPF module
to attach uprobes according to a regular expression. For example:

```python
bpf = BPF(text="...")
bpf.attach_uprobe(name="c", sym_re=".*write$", fn_name="probe")
```

* python: Support regex in attach_tracepoint

Modify attach_tracepoint to take a regex argument, in which case
it enumerates all tracepoints matching that regex and attaches to
all of them. The logic for enumerating tracepoints should eventually
belong in libccc and be shared across all the tools (tplist, trace
and so on).

* cc: Fix termination condition bug in symbol enumeration

bcc_elf would not terminate the enumeration correctly when the
user-provided callback returned -1 but there were still more
sections remaining in the ELF to be enumerated.

* stackcount: Support uprobes and tracepoints

Refactored stackcount and added support for uprobes and tracepoints,
which also required changes to the BPF module. USDT support still
pending.

* bcc: Refactor symbol listing to use foreach-style

Refactor symbol listing from paging style to foreach-style with a
callback function per-symbol. Even though we're now performing a
callback from C to Python for each symbol, this is preferable to the
paging approach because we need all the symbols in the current use
case.

Also refactored `stackcount` slightly; only missing support for USDT
probes now.

* stackcount: Support per-process displays

For user-space functions, or when requested for kernel-space
functions or tracepoints, group the output by process. Toggled
with the -P switch, off by default (except for user-space).

* Fix rebase issues, print pid only when there is one

* stackcount: Add USDT support

Now, stackcount supports USDT tracepoints in addition to
kernel functions, user functions, and kernel tracepoints.
The format is the same as with the other general-purpose
tools (argdist, trace):

```
stackcount -p $(pidof node) u:node:gc*
stackcount -p 185 u:pthread:pthread_create
```

* stackcount: Update examples and man page

Add examples and man page documentation for kernel
tracepoints, USDT tracepoints, and other features.

* stackcount: Change printing format slightly

When -p is specified, don't print the comm and pid. Also,
when -P is specified for kernel probes (kprobes and
tracepoints), use -1 for symbol resolution so that we
don't try to resolve kernel functions as user symbols.
Finally, print the comm and pid at the end of the stack
output and not at the beginning.

Fixes #722, in which a USDT probe that has more than
one location and the type of the argument is a string
caused trace to potentially access an uninitialized
stack variable, thereby not passing BPF program
verification at load time.

* Remove tracepoint.py

The `Tracepoint` class which implements the necessary
support for the tracepoint kprobe-based hack is no
longer needed and can be removed.

* argdist: Native tracepoint support

This commit migrates argdist to use the native bcc/BPF
tracepoint support instead of the hackish kprobe-
based approach. The resulting programs are cleaner
and likely more efficient.

As a result of this change, there is a slight API
change in how argdist is used with tracepoints. To
access fields from the tracepoint structure, the user
is expected to use `args->field` directly. This
leverages most of the built-in bcc support for
generating the tracepoint probe function.

* trace: Native tracepoint support

This commit migrates trace to use the native bcc/BPF
tracepoint support instead of the hackish kprobe-
based approach. The resulting programs are cleaner
and likely more efficient.

As with argdist, users are now expected to use the
`args` structure pointer to access the tracepoint's
arguments.

For example:

```
trace 't:irq:irq_handler_entry (args->irq != 27) "irq %d", args->irq'
```

By default, argdist now clears the histograms or freq
count maps after each display interval. The new `-c`
option enables cumulative mode, where maps are not
cleared at each interval. This fixes #718.

When verbose mode is enabled, ask all USDT helper
objects to print out the argument helper functions,
which help retrieve the argument values for each
individual probe location. This can be useful for
debugging probes; the helper functions are part of
the loaded BPF program, so they need to be printed
in verbose mode.

Fixes the error message from `BPF._find_exe` which would
occur if argdist or trace had a naked executable name
not qualified with a path, such as:

```
trace 'r:bash:readline "%s", retval'
```

This is now supported again.