python: Enforce absolute imports for Python 3 compatibility

Change-Id: Ia88d7fd472f7aed9b97df81468211384981bf6c6
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15983
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

python: Update use of exec to work with Python 3

Python 3 uses 'exec(code, globals)' instead of 'exec code in
globals'. Switch to the newer syntax since it is supported by Python
2.7. Also, move check_tracing out of main to work around a bug in
Python 2.7.

Change-Id: I6d390160f58783e1b038a572b64cdf3ff09535fa
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15986
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

python: Use PyBind11 instead of SWIG for Python wrappers

Use the PyBind11 wrapping infrastructure instead of SWIG to generate
wrappers for functionality that needs to be exported to Python. This
has several benefits:

* PyBind11 can be redistributed with gem5, which means that we have
full control of the version used. This avoid a large number of
hard-to-debug SWIG issues we have seen in the past.

* PyBind11 doesn't rely on a custom C++ parser, instead it relies on
wrappers being explicitly declared in C++. The leads to slightly
more boiler-plate code in manually created wrappers, but doesn't
doesn't increase the overall code size. A big benefit is that this
avoids strange compilation errors when SWIG doesn't understand
modern language features.

* Unlike SWIG, there is no risk that the wrapper code incorporates
incorrect type casts (this has happened on numerous occasions in
the past) since these will result in compile-time errors.

As a part of this change, the mechanism to define exported methods has
been redesigned slightly. New methods can be exported either by
declaring them in the SimObject declaration and decorating them with
the cxxMethod decorator or by adding an instance of
PyBindMethod/PyBindProperty to the cxx_exports class variable. The
decorator has the added benefit of making it possible to add a
docstring and naming the method's parameters.

The new wrappers have the following known issues:

* Global events can't be memory managed correctly. This was the
case in SWIG as well.

Change-Id: I88c5a95b6cf6c32fa9e1ad31dfc08b2e8199a763
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Andreas Hansson <andreas.hansson@arm.com>
Reviewed-by: Andrew Bardsley <andrew.bardsley@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2231
Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Pierre-Yves Péneau <pierre-yves.peneau@lirmm.fr>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

python: Move native wrappers to the _m5 namespace

Swig wrappers for native objects currently share the _m5.internal name
space with Python code. This is undesirable if we ever want to switch
from Swig to some other framework for native binding (e.g., PyBind11
or Boost::Python). This changeset moves all of such wrappers to the
_m5 namespace, which is now reserved for native code.

Change-Id: I2d2bc12dbc05b57b7c5a75f072e08124413d77f3
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

swig: Fix issue with circular import in 2.0.9/2.0.10

This patch fixes an issue which prevented gem5 from running when built
using swig 2.0.9 and 2.0.10. The generated event.py tried to import
m5.internal which in turn relied on importing event. This patch seems
to fix the problem, and so far has not caused any other issues.

sim: Move the draining interface into a separate base class

This patch moves the draining interface from SimObject to a separate
class that can be used by any object needing draining. However,
objects not visible to the Python code (i.e., objects not deriving
from SimObject) still depend on their parents informing them when to
drain. This patch also gets rid of the CountedDrainEvent (which isn't
really an event) and replaces it with a DrainManager.

Python: Remove import for random

python: get rid of internal.enums package.

Move generated enums into internal.params, which gets
imported into object.params, restoring backward
compatibility for scripts that expect to find them there.

swig: make all generated files go into the m5.internal package

This is necessary because versions of swig older than 1.3.39 fail to
do the right thing and try to do relative imports for everything (even
with the package= option to %module). Instead of putting params in
the m5.internal.params package, put params in the m5.internal package
and make all param modules start with param_. Same thing for
m5.internal.enums.

Also, stop importing all generated params into m5.objects. They are
not necessary and now with everything using relative imports we wound
up with pollution of the namespace (where builtin-range got overridden).

scons: Stop building the big monolithic swigged params module
kill params.i and create a separate .i for each object (param, enums, etc.)

python: Improve support for python calling back to C++ member functions.
Add support for declaring SimObjects to swig so their members can be wrapped.
Make sim_object.i only contain declarations for SimObject.
Create system.i to contain declarations for System.
Update python code to properly call the C++ given the new changes.

Completely re-work how the scons framework incorporates swig
and python code into m5 to allow swig an python code to
easily added by any SConscript instead of just the one in
src/python. This provides SwigSource and PySource for
adding new files to m5 (similar to Source for C++). Also
provides SimObject for including files that contain SimObject
information and build the m5.objects __init__.py file.