This commit migrates softirqs to use kernel tracepoints instead of
kprobes. Because tracepoints only provide the vector number and not
the function name, we use a conversion table, which is borrowed from
kernel/softirq.c, to translate the vector number to a display name.
This table is expected to be fairly stable. Notably, new names have
not been added since approximately 2009, and the last rename (without
adding or removing a name) was in 2014.

Resolves #1031.

Fix compiler warning on redefined Macro

Miscellaneous style and code layout improvements

README.md: fix broken link to stacksnoop examples

Updates to Lua/BPF code generator

the BPF maps and pointers were previously
implicitly dereferenced whenever an operation
on them required a value and not a pointer.
the upside is that accessing map element data
didn’t require an explicit operation, the downside
is that it wasn’t possible to get the value
explicitly.

this makes it possible to dereference any pointer
and materialize the value in the register as long
as it’s shorter than register width using `ptr[0]`
element access operator.

the DW LD_ABS|IND is prohibited, so it is
implemented as a double W load with shift.
this is slow as it also has to undo the ntohl
semantics of W loads, but makes dissection of
64bit fields with absolute addressing possible 

the direct access to packet is implemented as
a `load_bytes(off, var)` built-in for basic support,
there is no implicit data loader using it yet

the packet can now use indirect addressing mode
using NET_OFF to read from network protocol off

it has convenience dissectors for IPv4 and IPv6,
that can be used like:

```
local net = pkt.net_off
if net.ver == 4 then
    local ip = net.ip
else
    local ip6 = net.ip6
end
```

Free demangle_name after use

docs: update list of XDP compatible drivers

Add missing nfp driver to the list.

While we're at it, add name and pointers for other drivers for which XDP
support is known to exist, but has not yet been pushed to the main
kernel branch.

Note that e1000e is not available online at this date, the link points
to an email stating that the patch could be provided upon request.

Extend cpp table API

* KVM hypercall analysis example

* Update README with KVM analysis example

When events were lost, we used to print a message to stderr, which is less useful.
Now, we allow attaching an optional callback that would be invoked when events
are lost, allowing the user's program to perform some additional processing.

Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@polito.it>

Before this commit there was not a specify way to handle a map of type
array. A workaround was to use it as a hash table with int as key type.

This commit creates a new class (BPFArrayTable) that allows to get and
update the value of an element.
Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@polito.it>

This commit extends the api for hash tables allowing to get, update and
delete elements
Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@polito.it>

RFC: rework of shared table into multiple classes

Add table_storage.h to list of installed files for external c++ linking.
Signed-off-by: Brenden Blanco <bblanco@gmail.com>

Adds a reference to the ts_ member, for use by BPF class to access the
storage object and perform lookups.

Note that get_hash_table/get_stack_table don't have an error return, so
failure to lookup the table name will result in undefined behavior
(which is actually the case prior to this commit as well).

Also update indentation per clang-format
Signed-off-by: Brenden Blanco <bblanco@gmail.com>

Adds a TableStorage class for use by language frontends to store/access
references to loaded bpf maps. Includes support for shared and
namespaced maps, in a directory-like hierarchy.

Add a FileDesc helper class to automatically wrap open file descriptors.
The object prevents implicit copying of the fd (allows only
rvalue/move()), and takes care of the close() call.

Add a reference implementation of a TableStorageImpl that performs the
current default behavior expected by BPF_TABLE_PUBLIC, which is to share
maps between BPFModules in the same-process only. A stub implementation
for bpffs is started.

Update b/clang frontends to use this new class.

Also included is a framework for extracting the type information of maps
in an extensible way. Migrate BMapDeclVisitor to use this as the first
consumer.
Signed-off-by: Brenden Blanco <bblanco@gmail.com>

update tools diagram

funcslower: Trace slow kernel or user function calls

stacksnoop: Retire and move to examples/tracing