arch-arm: Fix Data Abort ISS when caused by Atomic operation

Data Aborts caused by an atomic instruction have a special rule for
their syndrome:
From a ISS point of view they count as read if a read to that address
would generate a fault; they count as writes otherwise (ISS.WnR bit)
This patch is implementing this in the TLB. For permission faults we
need to explicitly check if a read would trigger a fault
(e.g. checking for the AP bits) since permissions can allow read-only
accesses.
For other MMU exceptions (like translation faults) we are confident the
nature of the access doesn't affect the genration of a fault.
This means that if the access is atomic, we treat it as a read from an
ISS.WnR point of view.

Change-Id: Ia524aa6ae07f81513cdc26c516b5fd9b01a931c3
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20981
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

arch-arm: Implement ARMv8.1-HPD, Hierarchical permission disable

According to the armarm:
ARMv8.1-HPD introduces the facility to disable the hierarchical
attributes, APTable, PXNTable, and UXNTable, in the translation tables.
This disable has no effect on the NSTable bit. This feature is
mandatory in ARMv8.1 implementations.

This feature is added only to the VMSAv8-64 translation regimes. ARMv8.2
extends this to the AArch32 translation regimes, see ARMv8.2-AA32HPD.

The ID_AA64MMFR1_EL1.HPDS field identifies the support for ARMv8.1-HPD.

Change-Id: Ibbf589b82f2c1e4437b43252f8f633e8f6fb0b80
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/19610
Tested-by: kokoro <noreply+kokoro@google.com>

arch-arm: Clean Fault generation when processing Long Descriptor

A new shared method has been introduced: generateLongDescFault

Change-Id: I7eb6fa1347a6c2cf9cb11fd9f2137d983c4f7a40
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/19608
Tested-by: kokoro <noreply+kokoro@google.com>

arch-arm: Use ExceptionLevel type in TlbEntry

Replacing uint8_t with ExceptionLevel type in the arm TlbEntry. The
variable is representing the translation regime it is targeting.

Change-Id: Ifcd6e86c5d73f752e8476a2b7fda9ea74a0c7a3b
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/19488
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

arch-arm: Fix WalkerState,Descriptors default constructor

Those POD strutures are not initializing all members at construction.
This could lead to undefined behaviour

Change-Id: Iaa8afb126382b6bfbef686883a026262f24d5ca1
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>
Reviewed-by: Javier Setoain <javier.setoain@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/19149
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

mem: Minimize the use of MemObject.

MemObject doesn't provide anything beyond its base ClockedObject any
more, so this change removes it from most inheritance hierarchies.
Occasionally MemObject is replaced with SimObject when I was fairly
confident that the extra functionality of ClockedObject wasn't needed.

Change-Id: Ic014ab61e56402e62548e8c831eb16e26523fdce
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18289
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Maintainer: Gabe Black <gabeblack@google.com>

dev-arm: ambiguous use of getPort()

The recent introduction of getPort() creates a conflict with
the existing method used in arm MMU.

This patch rename the old getPort() in getDMAPort() according
to the returned value (DmaPort class type)

Change-Id: Ief3d83650fd6b08490522341631244be06e380ce
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17469
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

arch, cpu, dev, gpu, mem, sim, python: start using getPort.

Replace the getMasterPort, getSlavePort, and getEthPort functions
with getPort, and remove extraneous mechanisms that are no longer
necessary.

Change-Id: Iab7e3c02d2f3a0cf33e7e824e18c28646b5bc318
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17040
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

arch-arm: Correction for address size in EL1&0 translation

When doing EL0/1 translation in stage2, the
physical address size will be defined by the
hypervisor (via VTCR_EL2.ps, not TCR.ips).

See D10.2.121 of the ARM ARM.

Change-Id: Ic7df97c0f5950a648f7408cde3955a640b562c1d
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/12552
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>

arch-arm: Correction to address size in EL2/EL3

This commit corrects how the address size is
determined in EL2/EL3. Previously, TCR_ELx.ips
was used but this should be TCR_ELx.ps.

Change-Id: I7e5a2f376335532a1d1c8c74d12a416617474ae2
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/12551
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>

misc: Using smart pointers for memory Requests

This patch is changing the underlying type for RequestPtr from Request*
to shared_ptr<Request>. Having memory requests being managed by smart
pointers will simplify the code; it will also prevent memory leakage and
dangling pointers.

Change-Id: I7749af38a11ac8eb4d53d8df1252951e0890fde3
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/10996
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

arch-arm: Remove dead doingStage2 variable in PT walker

Change-Id: Iab5ecec56120c725847b2e462fd4793cfac87d3c
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/10815

arch-arm: Respect EL from translation type

There are cases where instructions request translations in the context
of a lower EL. This is currently not respected in the TLB and the page
table walker. Fix that.

Change-Id: Icd59657a1ecfd8bd75a001bb1a4e41a6f4808a36
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/10506
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>

arch-arm: Implement ARMv8.1 TTBR1_EL2 register

This patch implements the ARMv8.1 TTBR1_EL2 register, which is used for
getting the translation table base address when a Host Operating System
is running at EL2. (HCR_EL2.E2H = 1)

Change-Id: Ic0ab351cae3fd64855eda7c18c8757da0d7b8663
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/10382
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

arch-arm: Fix big endian support in do{Long,L1,L2}Descriptor

do{Long,L1,L2}Descriptor was not able to load descriptors correctly
for big-endian situations, causing recognised Descriptors. Added
big-endian related data conversions to correct them.

Change-Id: I0fdfbbdf56f94bbed19172acae1b6e4a0382b5a0
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/8144
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

arch-arm: Change function name for banked miscregs

This commit changes the function's name used for retrieving the index of a
security banked register given the flatten index. This will avoid confusion
with flattenRegId, which has a different purpose.

Change-Id: I470ffb55916cb7fc9f78e071a7f2e609c1829f1a
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/7982
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

arch,cpu: "virtualize" the TLB interface.

CPUs have historically instantiated the architecture specific version
of the TLBs to avoid a virtual function call, making them a little bit
more dependent on what the current ISA is. Some simple performance
measurement, the x86 twolf regression on the atomic CPU, shows that
there isn't actually any performance benefit, and if anything the
simulator goes slightly faster (although still within margin of error)
when the TLB functions are virtual.

This change switches everything outside of the architectures themselves
to use the generic BaseTLB type, and then inside the ISA for them to
cast that to their architecture specific type to call into architecture
specific interfaces.

The ARM TLB needed the most adjustment since it was using non-standard
translation function signatures. Specifically, they all took an extra
"type" parameter which defaulted to normal, and translateTiming
returned a Fault. translateTiming actually doesn't need to return a
Fault because everywhere that consumed it just stored it into a
structure which it then deleted(?), and the fault is stored in the
Translation object when the translation is done.

A little more work is needed to fully obviate the arch/tlb.hh header,
so the TheISA::TLB type is still visible outside of the ISAs.
Specifically, the TlbEntry type is used in the generic PageTable which
lives in src/mem.

Change-Id: I51b68ee74411f9af778317eff222f9349d2ed575
Reviewed-on: https://gem5-review.googlesource.com/6921
Maintainer: Gabe Black <gabeblack@google.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

misc: Updates for gcc7.2 for x86

GCC 7.2 is much stricter than previous GCC versions. The following changes
are needed:

* There is now a warning if there is an implicit fallthrough between two
case statments. C++17 adds the [[fallthrough]]; declaration. However,
to support non C++17 standards (i.e., C++11), we use M5_FALLTHROUGH.
M5_FALLTHROUGH checks for [[fallthrough]] compliant C++17 compiler and
if that doesn't exist, it defaults to nothing (no older compilers
generate warnings).
* The above resulted in a couple of bugs that were found. This is noted
in the review request on gerrit.
* throw() for dynamic exception specification is deprecated
* There were a couple of new uninitialized variable warnings
* Can no longer perform bitwise operations on a bool.
* Must now include <functional> for std::function
* Compiler bug for void* lambda. Changed to auto as work around. See
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82878

Change-Id: I5d4c782a4e133fa4cdb119e35d9aff68c6e2958e
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/5802
Reviewed-by: Gabe Black <gabeblack@google.com>

arm: Replace EventWrapper use with EventFunctionWrapper

Change-Id: I08de5f72513645d1fe92bde99fa205dde897e951
Signed-off-by: Sean Wilson <spwilson2@wisc.edu>
Reviewed-on: https://gem5-review.googlesource.com/3747
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

arm: Treat Write-Through Normal memory as Non-Cacheable

A completed write to a memory location that is Write-Through Cacheable
has to be visible to an external observer without the need of explicit
cache maintenance. This change adds support for Write-Through
Cacheable Normal memory and treats it as Non-cacheable. This incurs a
small penalty as accesses to the memory do not fill in the cache but
does not violate the properties of the memory type.

Change-Id: Iee17ef9d952a550be9ad660b1e60e9f6c4ef2c2d
Reviewed-by: Giacomo Gabrielli <giacomo.gabrielli@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/2280
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

arm: refactor page table walking

Introduce and use a lookup table.

Using fetchDescriptor() rather than DMA cleanly handles nested paging.

Change-Id: I69ec762f176bd752ba1040890e731826b58d15a6

arm: Fix stage 2 memory attribute checking in AArch64

Change-Id: I14c93a5460550051a12129e792a9a9bd522a145c

arm: Fix stage 2 determination in table walker

We recompute if we are doing a stage 2 walk inside of the table walker
but we have already figured it out in the tlb. Pass the information in
to the walk instead of recomputing it.

Change-Id: I39637ce99309b2ddbc30344d45ac9ebf6a203401

arm: Refactor aarch64 table walk logic to remove redundancy

The functional case is already handled within the fetchDescriptor()
function. We can thus use that function for both atomic and functional
mode when we start the table walk.

Change-Id: Iacaed28cd9024d259fd37a58150efd00ff94d86e

arm: add stage2 translation support

Change-Id: I8f7c09c7ec3a97149ebebf4b21471b244e6cecc1

arm: enable EL2 support

Change-Id: I59fa4fae98c33d9e5c2185382e1411911d27d341

sim: Call regStats of base-class as well

We want to extend the stats of objects hierarchically and thus it is necessary
to register the statistics of the base-class(es), as well. For now, these are
empty, but generic stats will be added there.

Patch originally provided by Akash Bagdia at ARM Ltd.

arm: refactor page table format determination

In particular, when EL0 is in AArch32 but EL1 is AArch64, AArch64
memory translation must be used. This is essential for typical
AArch64/32 interworking use cases.

arm: Refactor the TLB test interface

Refactor the TLB and page table walker test interface to use a dynamic
registration mechanism. Instead of patching a couple of empty methods
to wire up a TLB tester, this change allows such testers to register
themselves using the setTestInterface() method.

arm: Add secure flag to TableWalker request when needed

sim: Refactor and simplify the drain API

The drain() call currently passes around a DrainManager pointer, which
is now completely pointless since there is only ever one global
DrainManager in the system. It also contains vestiges from the time
when SimObjects had to keep track of their child objects that needed
draining.

This changeset moves all of the DrainState handling to the Drainable
base class and changes the drain() and drainResume() calls to reflect
this. Particularly, the drain() call has been updated to take no
parameters (the DrainManager argument isn't needed) and return a
DrainState instead of an unsigned integer (there is no point returning
anything other than 0 or 1 any more). Drainable objects should return
either DrainState::Draining (equivalent to returning 1 in the old
system) if they need more time to drain or DrainState::Drained
(equivalent to returning 0 in the old system) if they are already in a
consistent state. Returning DrainState::Running is considered an
error.

Drain done signalling is now done through the signalDrainDone() method
in the Drainable class instead of using the DrainManager directly. The
new call checks if the state of the object is DrainState::Draining
before notifying the drain manager. This means that it is safe to call
signalDrainDone() without first checking if the simulator has
requested draining. The intention here is to reduce the code needed to
implement draining in simple objects.

sim: Make the drain state a global typed enum

The drain state enum is currently a part of the Drainable
interface. The same state machine will be used by the DrainManager to
identify the global state of the simulator. Make the drain state a
global typed enum to better cater for this usage scenario.

arm: Cleanup arch headers to remove dma_device.hh dependency

Break the dependency on dma_device.hh by forward-declaring DmaPort in
the relevant header.

arm: Identify table-walker requests

This patch ensures all page-table walks are flagged as such.

arm: Share a port for the two table walker objects

This patch changes how the MMU and table walkers are created such that
a single port is used to connect the MMU and the TLBs to the memory
system. Previously two ports were needed as there are two table walker
objects (stage one and stage two), and they both had a port. Now the
port itself is moved to the Stage2MMU, and each TableWalker is simply
using the port from the parent.

By using the same port we also remove the need for having an
additional crossbar joining the two ports before the walker cache or
the L2. This simplifies the creation of the CPU cache topology in
BaseCPU.py considerably. Moreover, for naming and symmetry reasons,
the TLB walker port is connected through the stage-one table walker
thus making the naming identical to x86. Along the same line, we use
the stage-one table walker to generate the master id that is used by
all TLB-related requests.

arm: Add stats to table walker

This patch adds table walker stats for:
- Walk events
- Instruction vs Data
- Page size histogram
- Wait time and service time histograms
- Pending requests histogram (per cycle) - measures dist. of L
(p(1..) = how often busy, p(0) = how often idle)
- Squashes, before starting and after completion

arm: Fix TLB ignoring faults when table walking

This patch fixes a case where the Minor CPU can deadlock due to the lack
of a response to TLB request because of a bug in fault handling in the ARM
table walker.

TableWalker::processWalkWrapper is the scheduler-called wrapper which
handles deferred walks which calls to TableWalker::wait cannot immediately
process. The handling of faults generated by processWalk{AArch64,LPAE,}
calls in those two functions is is different. processWalkWrapper ignores
fault returns from processWalk... which can lead to ::finish not being
called on a translation.

This fix provides fault handling in processWalkWrapper similar to that
found in the leaf functions which BaseTLB::Translation::finish.

arm: Fixes based on UBSan and static analysis

Another churn to clean up undefined behaviour, mostly ARM, but some
parts also touching the generic part of the code base.

Most of the fixes are simply ensuring that proper intialisation. One
of the more subtle changes is the return type of the sign-extension,
which is changed to uint64_t. This is to avoid shifting negative
values (undefined behaviour) in the ISA code.

arm, mem: Fix drain bug and provide drain prints for more components.

arch: Use shared_ptr for all Faults

This patch takes quite a large step in transitioning from the ad-hoc
RefCountingPtr to the c++11 shared_ptr by adopting its use for all
Faults. There are no changes in behaviour, and the code modifications
are mostly just replacing "new" with "make_shared".

arm: Use MiscRegIndex rather than int when flattening

Some additional type checking to avoid future issues.

style: Fix line continuation, especially in debug messages

This patch closes a number of space gaps in debug messages caused by
the incorrect use of line continuation within strings. (There's also
one consistency change to a similar, but correct, use of line
continuation)

arm: support 16kb vm granules

arm: Handle functional TLB walks properly

The table walker code currently accounts for two types of walks,
Atomic and Timing, and treats them differently. Atomic walks keep a
single instance of WalkerState around for all walks to use in
currState. Timing mode keeps a queue of in-flight WalkerStates and
maintains currState as NULL between walks.

If a functional walk is done during Timing mode, it is treated as an
atomic walk and either creates a persistent WalkerState if in between
Timing walks, or stomps an existing currState for an in-progress
Timing walk.

This patch distinguishes functional walks as being able to exist at
any time and sets up a temporary WalkerState for its exclusive use and
then cleans up when finished, leaving any in progress Atomic or Timing
walks undisturbed.

arm: Add support for ARMv8 (AArch64 & AArch32)

Note: AArch64 and AArch32 interworking is not supported. If you use an AArch64
kernel you are restricted to AArch64 user-mode binaries. This will be addressed
in a later patch.

Note: Virtualization is only supported in AArch32 mode. This will also be fixed
in a later patch.

Contributors:
Giacomo Gabrielli (TrustZone, LPAE, system-level AArch64, AArch64 NEON, validation)
Thomas Grocutt (AArch32 Virtualization, AArch64 FP, validation)
Mbou Eyole (AArch64 NEON, validation)
Ali Saidi (AArch64 Linux support, code integration, validation)
Edmund Grimley-Evans (AArch64 FP)
William Wang (AArch64 Linux support)
Rene De Jong (AArch64 Linux support, performance opt.)
Matt Horsnell (AArch64 MP, validation)
Matt Evans (device models, code integration, validation)
Chris Adeniyi-Jones (AArch64 syscall-emulation)
Prakash Ramrakhyani (validation)
Dam Sunwoo (validation)
Chander Sudanthi (validation)
Stephan Diestelhorst (validation)
Andreas Hansson (code integration, performance opt.)
Eric Van Hensbergen (performance opt.)
Gabe Black

mem: per-thread cache occupancy and per-block ages

This patch enables tracking of cache occupancy per thread along with
ages (in buckets) per cache blocks. Cache occupancy stats are
recalculated on each stat dump.

arm: fix a page table walker issue where a page could be translated multiple times

If multiple memory operations to the same page are miss the TLB they are
all inserted into the page table queue and before this change could result
in multiple uncessesary walks as well as duplicate enteries being inserted
into the TLB.

sim: Add a system-global option to bypass caches

Virtualized CPUs and the fastmem mode of the atomic CPU require direct
access to physical memory. We currently require caches to be disabled
when using them to prevent chaos. This is not ideal when switching
between hardware virutalized CPUs and other CPU models as it would
require a configuration change on each switch. This changeset
introduces a new version of the atomic memory mode,
'atomic_noncaching', where memory accesses are inserted into the
memory system as atomic accesses, but bypass caches.

To make memory mode tests cleaner, the following methods are added to
the System class:

* isAtomicMode() -- True if the memory mode is 'atomic' or 'direct'.
* isTimingMode() -- True if the memory mode is 'timing'.
* bypassCaches() -- True if caches should be bypassed.

The old getMemoryMode() and setMemoryMode() methods should never be
used from the C++ world anymore.

arm: Fix draining of the pagetable walker when squashing

Since the page table walker only checks if a drain has completed in
doL1DescriptorWrapper() and doL2DescriptorWrapper(), it sometimes
looses track of a drain request if there is a squash. This changeset
adds a completeDrain() call after squashing requests in the pending
queue, which fixes this issue.

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.

arm: Use table walker clock that is inherited from CPU

This patch simplifies the scheduling of the next walk for the ARM
table walker. Previously it used the CPU clock, but as the table
walker inherits the clock from the CPU, it is cleaner to simply use
its own clock (which is the same).

Port: Add protocol-agnostic ports in the port hierarchy

This patch adds an additional level of ports in the inheritance
hierarchy, separating out the protocol-specific and protocl-agnostic
parts. All the functionality related to the binding of ports is now
confined to use BaseMaster/BaseSlavePorts, and all the
protocol-specific parts stay in the Master/SlavePort. In the future it
will be possible to add other protocol-specific implementations.

The functions used in the binding of ports, i.e. getMaster/SlavePort
now use the base classes, and the index parameter is updated to use
the PortID typedef with the symbolic InvalidPortID as the default.

ARM: Squash outstanding walks when instructions are squashed.

Clock: Add a Cycles wrapper class and use where applicable

This patch addresses the comments and feedback on the preceding patch
that reworks the clocks and now more clearly shows where cycles
(relative cycle counts) are used to express time.

Instead of bumping the existing patch I chose to make this a separate
patch, merely to try and focus the discussion around a smaller set of
changes. The two patches will be pushed together though.

This changes done as part of this patch are mostly following directly
from the introduction of the wrapper class, and change enough code to
make things compile and run again. There are definitely more places
where int/uint/Tick is still used to represent cycles, and it will
take some time to chase them all down. Similarly, a lot of parameters
should be changed from Param.Tick and Param.Unsigned to
Param.Cycles.

In addition, the use of curTick is questionable as there should not be
an absolute cycle. Potential solutions can be built on top of this
patch. There is a similar situation in the o3 CPU where
lastRunningCycle is currently counting in Cycles, and is still an
absolute time. More discussion to be had in other words.

An additional change that would be appropriate in the future is to
perform a similar wrapping of Tick and probably also introduce a
Ticks class along with suitable operators for all these classes.

Clock: Rework clocks to avoid tick-to-cycle transformations

This patch introduces the notion of a clock update function that aims
to avoid costly divisions when turning the current tick into a
cycle. Each clocked object advances a private (hidden) cycle member
and a tick member and uses these to implement functions for getting
the tick of the next cycle, or the tick of a cycle some time in the
future.

In the different modules using the clocks, changes are made to avoid
counting in ticks only to later translate to cycles. There are a few
oddities in how the O3 and inorder CPU count idle cycles, as seen by a
few locations where a cycle is subtracted in the calculation. This is
done such that the regression does not change any stats, but should be
revisited in a future patch.

Another, much needed, change that is not done as part of this patch is
to introduce a new typedef uint64_t Cycle to be able to at least hint
at the unit of the variables counting Ticks vs Cycles. This will be
done as a follow-up patch.

As an additional follow up, the thread context still uses ticks for
the book keeping of last activate and last suspend and this should
probably also be changed into cycles as well.

Packet: Remove NACKs from packet and its use in endpoints

This patch removes the NACK frrom the packet as there is no longer any
module in the system that issues them (the bridge was the only one and
the previous patch removes that).

The handling of NACKs was mostly avoided throughout the code base, by
using e.g. panic or assert false, but in a few locations the NACKs
were actually dealt with (although NACKs never occured in any of the
regressions). Most notably, the DMA port will now never receive a NACK
and the backoff time is thus never changed. As a consequence, the
entire backoff mechanism (similar to a PCI bus) is now removed and the
DMA port entirely relies on the bus performing the arbitration and
issuing a retry when appropriate. This is more in line with e.g. PCIe.

Surprisingly, this patch has no impact on any of the regressions. As
mentioned in the patch that removes the NACK from the bridge, a
follow-up patch should change the request and response buffer size for
at least one regression to also verify that the system behaves as
expected when the bridge fills up.

O3,ARM: fix some problems with drain/switchout functionality and add Drain DPRINTFs

This patch fixes some problems with the drain/switchout functionality
for the O3 cpu and for the ARM ISA and adds some useful debug print
statements.

This is an incremental fix as there are still a few bugs/mem leaks with the
switchout code. Particularly when switching from an O3CPU to a
TimingSimpleCPU. However, when switching from O3 to O3 cores with the ARM ISA
I haven't encountered any more assertion failures; now the kernel will
typically panic inside of simulation.

MEM: Add a snooping DMA port subclass for table walker

This patch makes the (device) DmaPort non-snooping and removes the
recvSnoop constructor parameter and instead introduces a
SnoopingDmaPort subclass for the ARM table walker.

Functionality is unchanged, as are the stats, and the patch merely
clarifies that the normal DMA ports are not snooping (although they
may issue requests that are snooped by others, as done with PCI, PCIe,
AMBA4 ACE etc).

Currently this port is declared in the ARM table walker as it is not
used anywhere else. If other ports were to have similar behaviour it
could be moved in a future patch.

MEM: Remove the Broadcast destination from the packet

This patch simplifies the packet by removing the broadcast flag and
instead more firmly relying on (and enforcing) the semantics of
transactions in the classic memory system, i.e. request packets are
routed from a master to a slave based on the address, and when they
are created they have neither a valid source, nor destination. On
their way to the slave, the request packet is updated with a source
field for all modules that multiplex packets from multiple master
(e.g. a bus). When a request packet is turned into a response packet
(at the final slave), it moves the potentially populated source field
to the destination field, and the response packet is routed through
any multiplexing components back to the master based on the
destination field.

Modules that connect multiplexing components, such as caches and
bridges store any existing source and destination field in the sender
state as a stack (just as before).

The packet constructor is simplified in that there is no longer a need
to pass the Packet::Broadcast as the destination (this was always the
case for the classic memory system). In the case of Ruby, rather than
using the parameter to the constructor we now rely on setDest, as
there is already another three-argument constructor in the packet
class.

In many places where the packet information was printed as part of
DPRINTFs, request packets would be printed with a numeric "dest" that
would always be -1 (Broadcast) and that field is now removed from the
printing.

MEM: Introduce the master/slave port sub-classes in C++

This patch introduces the notion of a master and slave port in the C++
code, thus bringing the previous classification from the Python
classes into the corresponding simulation objects and memory objects.

The patch enables us to classify behaviours into the two bins and add
assumptions and enfore compliance, also simplifying the two
interfaces. As a starting point, isSnooping is confined to a master
port, and getAddrRanges to slave ports. More of these specilisations
are to come in later patches.

The getPort function is not getMasterPort and getSlavePort, and
returns a port reference rather than a pointer as NULL would never be
a valid return value. The default implementation of these two
functions is placed in MemObject, and calls fatal.

The one drawback with this specific patch is that it requires some
code duplication, e.g. QueuedPort becomes QueuedMasterPort and
QueuedSlavePort, and BusPort becomes BusMasterPort and BusSlavePort
(avoiding multiple inheritance). With the later introduction of the
port interfaces, moving the functionality outside the port itself, a
lot of the duplicated code will disappear again.

MEM: Move port creation to the memory object(s) construction

This patch moves all port creation from the getPort method to be
consistently done in the MemObject's constructor. This is possible
thanks to the Swig interface passing the length of the vector ports.
Previously there was a mix of: 1) creating the ports as members (at
object construction time) and using getPort for the name resolution,
or 2) dynamically creating the ports in the getPort call. This is now
uniform. Furthermore, objects that would not be complete without a
port have these ports as members rather than having pointers to
dynamically allocated ports.

This patch also enables an elaboration-time enumeration of all the
ports in the system which can be used to determine the masterId.

mem: Add a master ID to each request object.

This change adds a master id to each request object which can be
used identify every device in the system that is capable of issuing a request.
This is part of the way to removing the numCpus+1 stats in the cache and
replacing them with the master ids. This is one of a series of changes
that make way for the stats output to be changed to python.

CheckerCPU: Re-factor CheckerCPU to be compatible with current gem5

Brings the CheckerCPU back to life to allow FS and SE checking of the
O3CPU. These changes have only been tested with the ARM ISA. Other
ISAs potentially require modification.

Device: Make changes necessary to support a coherent page walker cache.

Adds the flag 'recvSnoops' which enables pagewalkers using DmaPorts,
to properly configure snoops.

ARM: Fix a memory leak with the table walker.

fix some build problems from prior changesets

includes: sort all includes

ARM: Fix table walk going on while ASID changes error

ARM: Fix bug that let two table walks occur in parallel.

O3: Fix a few bugs in the TableWalker object.

Uncacheable requests were set as such only in atomic mode.
currState->delayed is checked in place of currState->timing for resetting
currState in atomic mode.

Replace curTick global variable with accessor functions.
This step makes it easy to replace the accessor functions
(which still access a global variable) with ones that access
per-thread curTick values.

ARM: Support switchover with hardware table walkers

ARM: Add support for switching CPUs

ARM: Add checkpointing support

ARM: Don't return the result of a table walk the same cycle it's completed.

The L1 cache may have been accessed to provide this data, which confuses
it, if it ends up being accesses twice in one cycle. Instead wait 1 tick
which will force the timing simple CPU to forward to its next clock cycle
when the translation completes.

Also prevent multiple outstanding table walks from occuring at once.

ISA,CPU,etc: Create an ISA defined PC type that abstracts out ISA behaviors.



This change is a low level and pervasive reorganization of how PCs are managed
in M5. Back when Alpha was the only ISA, there were only 2 PCs to worry about,
the PC and the NPC, and the lsb of the PC signaled whether or not you were in
PAL mode. As other ISAs were added, we had to add an NNPC, micro PC and next
micropc, x86 and ARM introduced variable length instruction sets, and ARM
started to keep track of mode bits in the PC. Each CPU model handled PCs in
its own custom way that needed to be updated individually to handle the new
dimensions of variability, or, in the case of ARMs mode-bit-in-the-pc hack,
the complexity could be hidden in the ISA at the ISA implementation's expense.
Areas like the branch predictor hadn't been updated to handle branch delay
slots or micropcs, and it turns out that had introduced a significant (10s of
percent) performance bug in SPARC and to a lesser extend MIPS. Rather than
perpetuate the problem by reworking O3 again to handle the PC features needed
by x86, this change was introduced to rework PC handling in a more modular,
transparent, and hopefully efficient way.


PC type:

Rather than having the superset of all possible elements of PC state declared
in each of the CPU models, each ISA defines its own PCState type which has
exactly the elements it needs. A cross product of canned PCState classes are
defined in the new "generic" ISA directory for ISAs with/without delay slots
and microcode. These are either typedef-ed or subclassed by each ISA. To read
or write this structure through a *Context, you use the new pcState() accessor
which reads or writes depending on whether it has an argument. If you just
want the address of the current or next instruction or the current micro PC,
you can get those through read-only accessors on either the PCState type or
the *Contexts. These are instAddr(), nextInstAddr(), and microPC(). Note the
move away from readPC. That name is ambiguous since it's not clear whether or
not it should be the actual address to fetch from, or if it should have extra
bits in it like the PAL mode bit. Each class is free to define its own
functions to get at whatever values it needs however it needs to to be used in
ISA specific code. Eventually Alpha's PAL mode bit could be moved out of the
PC and into a separate field like ARM.

These types can be reset to a particular pc (where npc = pc +
sizeof(MachInst), nnpc = npc + sizeof(MachInst), upc = 0, nupc = 1 as
appropriate), printed, serialized, and compared. There is a branching()
function which encapsulates code in the CPU models that checked if an
instruction branched or not. Exactly what that means in the context of branch
delay slots which can skip an instruction when not taken is ambiguous, and
ideally this function and its uses can be eliminated. PCStates also generally
know how to advance themselves in various ways depending on if they point at
an instruction, a microop, or the last microop of a macroop. More on that
later.

Ideally, accessing all the PCs at once when setting them will improve
performance of M5 even though more data needs to be moved around. This is
because often all the PCs need to be manipulated together, and by getting them
all at once you avoid multiple function calls. Also, the PCs of a particular
thread will have spatial locality in the cache. Previously they were grouped
by element in arrays which spread out accesses.


Advancing the PC:

The PCs were previously managed entirely by the CPU which had to know about PC
semantics, try to figure out which dimension to increment the PC in, what to
set NPC/NNPC, etc. These decisions are best left to the ISA in conjunction
with the PC type itself. Because most of the information about how to
increment the PC (mainly what type of instruction it refers to) is contained
in the instruction object, a new advancePC virtual function was added to the
StaticInst class. Subclasses provide an implementation that moves around the
right element of the PC with a minimal amount of decision making. In ISAs like
Alpha, the instructions always simply assign NPC to PC without having to worry
about micropcs, nnpcs, etc. The added cost of a virtual function call should
be outweighed by not having to figure out as much about what to do with the
PCs and mucking around with the extra elements.

One drawback of making the StaticInsts advance the PC is that you have to
actually have one to advance the PC. This would, superficially, seem to
require decoding an instruction before fetch could advance. This is, as far as
I can tell, realistic. fetch would advance through memory addresses, not PCs,
perhaps predicting new memory addresses using existing ones. More
sophisticated decisions about control flow would be made later on, after the
instruction was decoded, and handed back to fetch. If branching needs to
happen, some amount of decoding needs to happen to see that it's a branch,
what the target is, etc. This could get a little more complicated if that gets
done by the predecoder, but I'm choosing to ignore that for now.


Variable length instructions:

To handle variable length instructions in x86 and ARM, the predecoder now
takes in the current PC by reference to the getExtMachInst function. It can
modify the PC however it needs to (by setting NPC to be the PC + instruction
length, for instance). This could be improved since the CPU doesn't know if
the PC was modified and always has to write it back.


ISA parser:

To support the new API, all PC related operand types were removed from the
parser and replaced with a PCState type. There are two warts on this
implementation. First, as with all the other operand types, the PCState still
has to have a valid operand type even though it doesn't use it. Second, using
syntax like PCS.npc(target) doesn't work for two reasons, this looks like the
syntax for operand type overriding, and the parser can't figure out if you're
reading or writing. Instructions that use the PCS operand (which I've
consistently called it) need to first read it into a local variable,
manipulate it, and then write it back out.


Return address stack:

The return address stack needed a little extra help because, in the presence
of branch delay slots, it has to merge together elements of the return PC and
the call PC. To handle that, a buildRetPC utility function was added. There
are basically only two versions in all the ISAs, but it didn't seem short
enough to put into the generic ISA directory. Also, the branch predictor code
in O3 and InOrder were adjusted so that they always store the PC of the actual
call instruction in the RAS, not the next PC. If the call instruction is a
microop, the next PC refers to the next microop in the same macroop which is
probably not desirable. The buildRetPC function advances the PC intelligently
to the next macroop (in an ISA specific way) so that that case works.


Change in stats:

There were no change in stats except in MIPS and SPARC in the O3 model. MIPS
runs in about 9% fewer ticks. SPARC runs with 30%-50% fewer ticks, which could
likely be improved further by setting call/return instruction flags and taking
advantage of the RAS.


TODO:

Add != operators to the PCState classes, defined trivially to be !(a==b).
Smooth out places where PCs are split apart, passed around, and put back
together later. I think this might happen in SPARC's fault code. Add ISA
specific constructors that allow setting PC elements without calling a bunch
of accessors. Try to eliminate the need for the branching() function. Factor
out Alpha's PAL mode pc bit into a separate flag field, and eliminate places
where it's blindly masked out or tested in the PC.

ARM: Implement functional virtual to physical address translation
for debugging and program introspection.

ARM: Seperate the queues of L1 and L2 walker states.

ARM: Make sure that software prefetch instructions can't change the state of the TLB

ARM: Fix Uncachable TLB requests and decoding of xn bit

ARM: Fix an un-initialized variable bug

ARM: Finish the timing translation when taking a fault.

ARM: Use a stl queue for the table walker state

Compiler: Fixes for GCC 4.5.

ARM: Allow multiple outstanding TLB walks to queue.

ARM TLB: Fix bug in memAttrs getting a bogus thread context

ARM: Support table walks in timing mode.

ARM: Added support for Access Flag and some CP15 regs (V2PCWPR, V2PCWPW, V2PCWUR, V2PCWUW,...)

ARM: Some TLB bug fixes.

ARM: Implement the ARM TLB/Tablewalker. Needs performance improvements.