python: Don't assume SimObjects live in the global namespace

The importer in Python 3 doesn't like the way we import SimObjects
from the global namespace. Convert the existing SimObject declarations
to import from m5.objects. As a side-effect, this makes these files
consistent with configuration files.

Change-Id: I11153502b430822130722839e1fa767b82a027aa
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15981
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.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>

sim, kvm: make KvmVM a System parameter

A KVM VM is typically a child of the System object already, but for
solving future issues with configuration graph resolution, the most
logical way to keep track of this object is for it to be an actual
parameter of the System object.

Change-Id: I965ded22203ff8667db9ca02de0042ff1c772220
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

sim: Remove redundant export_method_cxx_predecls

The headers declared in export_method_cxx_predecls are redundant since a
SimObject's main header is automatically included.

Change-Id: Ied9e84630b36960e54efe91d16f8c66fba7e0da0
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Joe Gross <joseph.gross@amd.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

kvm: Add an option to force context sync on kvm entry/exit

This changeset adds an option to force the kvm-based CPUs to always
synchronize the gem5 thread context representation on entry/exit into
the kernel. This is very useful for debugging. Unfortunately, it is
also the only way to get reliable register contents when using remote
gdb functionality. The long-term solution for the latter would be to
implement a kvm-specific thread context.

Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Alexandru Dutu <alexandru.dutu@amd.com>

sim: Refactor the serialization base class

Objects that are can be serialized are supposed to inherit from the
Serializable class. This class is meant to provide a unified API for
such objects. However, so far it has mainly been used by SimObjects
due to some fundamental design limitations. This changeset redesigns
to the serialization interface to make it more generic and hide the
underlying checkpoint storage. Specifically:

* Add a set of APIs to serialize into a subsection of the current
object. Previously, objects that needed this functionality would
use ad-hoc solutions using nameOut() and section name
generation. In the new world, an object that implements the
interface has the methods serializeSection() and
unserializeSection() that serialize into a named /subsection/ of
the current object. Calling serialize() serializes an object into
the current section.

* Move the name() method from Serializable to SimObject as it is no
longer needed for serialization. The fully qualified section name
is generated by the main serialization code on the fly as objects
serialize sub-objects.

* Add a scoped ScopedCheckpointSection helper class. Some objects
need to serialize data structures, that are not deriving from
Serializable, into subsections. Previously, this was done using
nameOut() and manual section name generation. To simplify this,
this changeset introduces a ScopedCheckpointSection() helper
class. When this class is instantiated, it adds a new /subsection/
and subsequent serialization calls during the lifetime of this
helper class happen inside this section (or a subsection in case
of nested sections).

* The serialize() call is now const which prevents accidental state
manipulation during serialization. Objects that rely on modifying
state can use the serializeOld() call instead. The default
implementation simply calls serialize(). Note: The old-style calls
need to be explicitly called using the
serializeOld()/serializeSectionOld() style APIs. These are used by
default when serializing SimObjects.

* Both the input and output checkpoints now use their own named
types. This hides underlying checkpoint implementation from
objects that need checkpointing and makes it easier to change the
underlying checkpoint storage code.

kvm: Separate host frequency from simulated CPU frequency

We used to use the KVM CPU's clock to specify the host frequency. This
was not ideal for several reasons. One of them being that the clock
parameter of a CPU determines the frequency of some of the components
connected to the CPU. This changeset adds a separate hostFreq
parameter that should be used to specify the host frequency until we
add code to autodetect it. The hostFactor should still be used to
specify the conversion factor between the host performance and that of
the simulated system.

kvm: Add support for disabling coalesced MMIO

Add the option useCoalescedMMIO to the BaseKvmCPU. The default
behavior is to disable coalesced MMIO since this hasn't been heavily
tested.

kvm: Add experimental support for a perf-based execution timer

Add support for using the CPU cycle counter instead of a normal POSIX
timer to generate timed exits to gem5. This should, in theory, provide
better resolution when requesting timer signals.

The perf-based timer requires a fairly recent kernel since it requires
a working PERF_EVENT_IOC_PERIOD ioctl. This ioctl has existed in the
kernel for a long time, but it used to be completely broken due to an
inverted match when the kernel copied things from user
space. Additionally, the ioctl does not change the sample period
correctly on all kernel versions which implement it. It is currently
only known to work reliably on kernel version 3.7 and above on ARM.

kvm: Basic support for hardware virtualized CPUs

This changeset introduces the architecture independent parts required
to support KVM-accelerated CPUs. It introduces two new simulation
objects:

KvmVM -- The KVM VM is a component shared between all CPUs in a shared
memory domain. It is typically instantiated as a child of the
system object in the simulation hierarchy. It provides access
to KVM VM specific interfaces.

BaseKvmCPU -- Abstract base class for all KVM-based CPUs. Architecture
dependent CPU implementations inherit from this class
and implement the following methods:

* updateKvmState() -- Update the
architecture-dependent KVM state from the gem5
thread context associated with the CPU.

* updateThreadContext() -- Update the thread context
from the architecture-dependent KVM state.

* dump() -- Dump the KVM state using (optional).

In order to deliver interrupts to the guest, CPU
implementations typically override the tick() method and
check for, and deliver, interrupts prior to entering
KVM.

Hardware-virutalized CPU currently have the following limitations:
* SE mode is not supported.
* PC events are not supported.
* Timing statistics are currently very limited. The current approach
simply scales the host cycles with a user-configurable factor.
* The simulated system must not contain any caches.
* Since cycle counts are approximate, there is no way to request an
exact number of cycles (or instructions) to be executed by the CPU.
* Hardware virtualized CPUs and gem5 CPUs must not execute at the
same time in the same simulator instance.
* Only single-CPU systems can be simulated.
* Remote GDB connections to the guest system are not supported.

Additionally, m5ops requires an architecture specific interface and
might not be supported.