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2018-06-14arch: support issuing Atomic Mem Operation (AMO) requestsTuan Ta
This patch adds two new functions named amoMemAtomic used in Atomic CPU model and initiateMemAMO used in Timing CPU models to issue AMO requests to the memory system. Change-Id: I962bdc0e5f25b72c170d96ebc136f29a2b230d5e Reviewed-on: https://gem5-review.googlesource.com/8186 Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com> Reviewed-by: Jason Lowe-Power <jason@lowepower.com> Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>
2018-06-11misc: Using smart pointers for memory RequestsGiacomo Travaglini
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>
2018-06-11misc: Substitute pointer to Request with aliased RequestPtrGiacomo Travaglini
Every usage of Request* in the code has been replaced with the RequestPtr alias. This is a preparing patch for when RequestPtr will be the typdefed to a smart pointer to Request rather then a raw pointer to Request. Change-Id: I73cbaf2d96ea9313a590cdc731a25662950cd51a Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com> Reviewed-on: https://gem5-review.googlesource.com/10995 Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com> Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br> Maintainer: Anthony Gutierrez <anthony.gutierrez@amd.com>
2018-03-27arch: cpu: Make the ExtMachInst type a template argument in InstMap.Gabe Black
This doesn't completely hide the ISA specific ExtMachInst type inside the ISAs since it still gets applied in arch/generic, but it at least pulls it into the arch directory. Change-Id: Ic2188d59696530d7ecafdff0785d71867182701d Reviewed-on: https://gem5-review.googlesource.com/9403 Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Maintainer: Gabe Black <gabeblack@google.com>
2017-12-22arch,cpu: "virtualize" the TLB interface.Gabe Black
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>
2017-12-13arm,sparc,x86,base,cpu,sim: Replace the Twin(32|64)_t types with.Gabe Black
Replace them with std::array<>s. Change-Id: I76624c87a1cd9b21c386a96147a18de92b8a8a34 Reviewed-on: https://gem5-review.googlesource.com/6602 Maintainer: Gabe Black <gabeblack@google.com> Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
2017-12-04misc: Rename misc.(hh|cc) to logging.(hh|cc)Gabe Black
These files aren't a collection of miscellaneous stuff, they're the definition of the Logger interface, and a few utility macros for calling into that interface (panic, warn, etc.). Change-Id: I84267ac3f45896a83c0ef027f8f19c5e9a5667d1 Reviewed-on: https://gem5-review.googlesource.com/6226 Reviewed-by: Brandon Potter <Brandon.Potter@amd.com> Maintainer: Gabe Black <gabeblack@google.com>
2017-10-13mem: Signal the local monitor when clearing the global monitorNikos Nikoleris
ARM systems require the coordination of the global and local monitors. When the system is run without caches the global monitor is implemented in the abstract memory object. This change adds a callback from the abstract memory that notifies the local monitor when the global monitor is cleared. Additionally, for ARM systems the local monitor signals the event register and wakes the thread context up. Subsequent wait-for-event (WFE) instructions will be immediately signaled. Change-Id: If6c038f3a6bea7239ba4258f07f39c7f9a30500b Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-on: https://gem5-review.googlesource.com/3760 Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com> Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
2017-07-05cpu: Added interface for vector reg fileRekai Gonzalez-Alberquilla
This patch adds some more functionality to the cpu model and the arch to interface with the vector register file. This change consists mainly of augmenting ThreadContexts and ExecContexts with calls to get/set full vectors, underlying microarchitectural elements or lanes. Those are meant to interface with the vector register file. All classes that implement this interface also get an appropriate implementation. This requires implementing the vector register file for the different models using the VecRegContainer class. This change set also updates the Result abstraction to contemplate the possibility of having a vector as result. The changes also affect how the remote_gdb connection works. There are some (nasty) side effects, such as the need to define dummy numPhysVecRegs parameter values for architectures that do not implement vector extensions. Nathanael Premillieu's work with an increasing number of fixes and improvements of mine. Change-Id: Iee65f4e8b03abfe1e94e6940a51b68d0977fd5bb Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> [ Fix RISCV build issues and CC reg free list initialisation ] Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-on: https://gem5-review.googlesource.com/2705
2017-07-05arch: added generic vector registerRekai Gonzalez-Alberquilla
This commit adds a new generic vector register to have a cleaner implementation of SIMD ISAs. Nathanael's idea, Rekai's implementation. Change-Id: I60b250bba6423153b7e04d2e6988d517a70a3e6b Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-on: https://gem5-review.googlesource.com/2704 Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com> Reviewed-by: Tony Gutierrez <anthony.gutierrez@amd.com> Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2017-07-05arch, cpu: Architectural Register structural indexingNathanael Premillieu
Replace the unified register mapping with a structure associating a class and an index. It is now much easier to know which class of register the index is referring to. Also, when adding a new class there is no need to modify existing ones. Change-Id: I55b3ac80763702aa2cd3ed2cbff0a75ef7620373 Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> [ Fix RISCV build issues ] Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-on: https://gem5-review.googlesource.com/2700
2017-06-22arm,sim: fix context switch stats dumps for ARM64/LinuxPaul Rosenfeld
32bit and 64bit Linux have different arguments passed to the __switch_to() function that gem5 hooks into in order to collect context switch statistics. 64bit Linux provides the task_struct pointer to the next task that will be switched to, which means we don't have to look up the task_struct from thread_info as we do in 32bit ARM Linux. This patch adds a second set of accessors to ThreadInfo to extract details such as the pid, tgid, task name, etc., directly from a task_struct. The existing accessors maintain their existing behavior by first looking up the task_struct and then calling these new accessors. A 64-bit variant of the DumpStatsPCEvent class is added that uses these new accessors to get the task details for the context switch dumps directly from the task_struct passed to __switch_to(). Change-Id: I63c4b3e1ad64446751a91f6340901d5180d7382d Reviewed-on: https://gem5-review.googlesource.com/2640 Reviewed-by: Curtis Dunham <curtis.dunham@arm.com> Reviewed-by: Jason Lowe-Power <jason@lowepower.com> Reviewed-by: Pau Cabre <pau.cabre@metempsy.com> Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2017-02-27syscall_emul: [PATCH 15/22] add clone/execve for threading and multiprocess ↵Brandon Potter
simulations Modifies the clone system call and adds execve system call. Requires allowing processes to steal thread contexts from other processes in the same system object and the ability to detach pieces of process state (such as MemState) to allow dynamic sharing.
2017-02-27arch: Include generated decoder header after normal headersAndreas Sandberg
The generated decoder header defines macros that represent bit fields within instructions. These fields typically have short names that conflict with names in other header files. Include the generated header after all normal header to avoid this issue. Change-Id: I53d149b75432c20abdbf651e32c3c785d897973b 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>
2016-11-09style: [patch 1/22] use /r/3648/ to reorganize includesBrandon Potter
2016-08-15cpu, arch: fix the type used for the request flagsNikos Nikoleris
Change-Id: I183b9942929c873c3272ce6d1abd4ebc472c7132 Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
2016-02-06style: fix missing spaces in control statementsSteve Reinhardt
Result of running 'hg m5style --skip-all --fix-control -a'.
2016-01-17cpu. arch: add initiateMemRead() to ExecContext interfaceSteve Reinhardt
For historical reasons, the ExecContext interface had a single function, readMem(), that did two different things depending on whether the ExecContext supported atomic memory mode (i.e., AtomicSimpleCPU) or timing memory mode (all the other models). In the former case, it actually performed a memory read; in the latter case, it merely initiated a read access, and the read completion did not happen until later when a response packet arrived from the memory system. This led to some confusing things, including timing accesses being required to provide a pointer for the return data even though that pointer was only used in atomic mode. This patch splits this interface, adding a new initiateMemRead() function to the ExecContext interface to replace the timing-mode use of readMem(). For consistency and clarity, the readMemTiming() helper function in the ISA definitions is renamed to initiateMemRead() as well. For x86, where the access size is passed in explicitly, we can also get rid of the data parameter at this level. For other ISAs, where the access size is determined from the type of the data parameter, we have to keep the parameter for that purpose.
2016-01-17arch: don't call *Timing functions from *Atomic versionsSteve Reinhardt
The readMemAtomic/writeMemAtomic helper functions were calling readMemTiming/writeMemTiming respectively. This is functionally correct, since the *Timing functions are doing the same access initiation operation as the *Atomic functions (just that the *Atomic versions also complete the access in line). It also provides for some (very minimal) code reuse. Unfortunately, it's potentially pretty confusing, since it makes it look like the atomic accesses are somehow being converted to timing accesses. It also gets in the way of specializing the timing interface (as will be done in a future patch).
2015-10-12misc: Add explicit overrides and fix other clang >= 3.5 issuesAndreas Hansson
This patch adds explicit overrides as this is now required when using "-Wall" with clang >= 3.5, the latter now part of the most recent XCode. The patch consequently removes "virtual" for those methods where "override" is added. The latter should be enough of an indication. As part of this patch, a few minor issues that clang >= 3.5 complains about are also resolved (unused methods and variables).
2015-10-12misc: Remove redundant compiler-specific definesAndreas Hansson
This patch moves away from using M5_ATTR_OVERRIDE and the m5::hashmap (and similar) abstractions, as these are no longer needed with gcc 4.7 and clang 3.1 as minimum compiler versions.
2015-07-07sim: Refactor the serialization base classAndreas Sandberg
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.
2015-04-29arch, base, dev, kern, sym: FreeBSD supportRuslan Bukin
This adds support for FreeBSD/aarch64 FS and SE mode (basic set of syscalls only) Committed by: Nilay Vaish <nilay@cs.wisc.edu>
2015-02-11sim: Move the BaseTLB to src/arch/generic/Andreas Sandberg
The TLB-related code is generally architecture dependent and should live in the arch directory to signify that. --HG-- rename : src/sim/BaseTLB.py => src/arch/generic/BaseTLB.py rename : src/sim/tlb.cc => src/arch/generic/tlb.cc rename : src/sim/tlb.hh => src/arch/generic/tlb.hh
2014-11-23kvm, x86: Adding support for SE mode executionAlexandru Dutu
This patch adds methods in KvmCPU model to handle KVM exits caused by syscall instructions and page faults. These types of exits will be encountered if KvmCPU is run in SE mode.
2014-11-14arm: Fixes based on UBSan and static analysisAndreas Hansson
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.
2014-10-16arch: Use shared_ptr for all FaultsAndreas Hansson
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".
2014-09-27arch: Use const StaticInstPtr references where possibleAndreas Hansson
This patch optimises the passing of StaticInstPtr by avoiding copying the reference-counting pointer. This avoids first incrementing and then decrementing the reference-counting pointer.
2014-08-26base: Replace the internal varargs stuff with C++11 constructsAndreas Sandberg
We currently use our own home-baked support for type-safe variadic functions. This is confusing and somewhat limited (e.g., cprintf only supports a limited number of arguments). This changeset converts all uses of our internal varargs support to use C++11 variadic macros.
2014-01-24mem: Remove explict cast from memhelper.Ali Saidi
Previously we were casting the result type to the the memory type which is incorrect for things like dual-memory operations which still return a single result.
2013-10-15mem: Use a flag instead of address bit 63 for generic IPRsAndreas Sandberg
Using address bit 63 to identify generic IPRs caused problems on SPARC, where IPRs are heavily used. This changeset redefines how generic IPRs are identified. Instead of using bit 63, we now use a separate flag (GENERIC_IPR) a memory request.
2013-09-30arch: Add support for m5ops using mmapped IPRsAndreas Sandberg
In order to support m5ops on virtualized CPUs, we need to either intercept hypercall instructions or provide a memory mapped m5ops interface. Since KVM does not normally pass the results of hypercalls to userspace, which makes that method unfeasible. This changeset introduces support for m5ops using memory mapped mmapped IPRs. This is implemented by adding a class of "generic" IPRs which are handled by architecture-independent code. Such IPRs always have bit 63 set and are handled by handleGenericIprRead() and handleGenericIprWrite(). Platform specific impementations of handleIprRead and handleIprWrite should use GenericISA::isGenericIprAccess to determine if an IPR address should be handled by the generic code instead of the architecture-specific code. Platforms that don't need their own IPR support can reuse GenericISA::handleIprRead() and GenericISA::handleIprWrite().
2013-09-04arch: Resurrect the NOISA build target and rename it NULLAndreas Hansson
This patch makes it possible to once again build gem5 without any ISA. The main purpose is to enable work around the interconnect and memory system without having to build any CPU models or device models. The regress script is updated to include the NULL ISA target. Currently no regressions make use of it, but all the testers could (and perhaps should) transition to it. --HG-- rename : build_opts/NOISA => build_opts/NULL rename : src/arch/noisa/SConsopts => src/arch/null/SConsopts rename : src/arch/noisa/cpu_dummy.hh => src/arch/null/cpu_dummy.hh rename : src/cpu/intr_control.cc => src/cpu/intr_control_noisa.cc
2013-01-07arch: Fix broken M5VarArgsFault initializationAndreas Sandberg
At least gcc 4.4.3 seems to get confused by the use of func both as a template parameter and a member variable in the M5VarArgsFault class. This causes the value of the member variable func to be unpredictable in M5VarArgsFault objects. This changeset renames the template parameter to remove this ambiguity.
2012-11-02ISA: generic Linux thread info supportDam Sunwoo
This patch takes the Linux thread info support scattered across different ISA implementations (currently in ARM, ALPHA, and MIPS), and unifies them into a single file. Adds a few more helper functions to read out TGID, mm, etc. ISA-specific information (e.g., ALPHA PCBB register) is now moved to the corresponding isa_traits.hh files.
2012-05-26ISA,CPU: Generalize and split out the components of the decode cache.Gabe Black
This will allow it to be specialized by the ISAs. The existing caching scheme is provided by the BasicDecodeCache in the GenericISA namespace and is built from the generalized components. --HG-- rename : src/cpu/decode_cache.cc => src/arch/generic/decode_cache.cc
2012-05-25ISA: Make the decode function part of the ISA's decoder.Gabe Black
2012-05-25Decode: Make the Decoder class defined per ISA.Gabe Black
--HG-- rename : src/cpu/decode.cc => src/arch/generic/decoder.cc rename : src/cpu/decode.hh => src/arch/generic/decoder.hh
2012-01-31clang: Enable compiling gem5 using clang 2.9 and 3.0Koan-Sin Tan
This patch adds the necessary flags to the SConstruct and SConscript files for compiling using clang 2.9 and later (on Ubuntu et al and OSX XCode 4.2), and also cleans up a bunch of compiler warnings found by clang. Most of the warnings are related to hidden virtual functions, comparisons with unsigneds >= 0, and if-statements with empty bodies. A number of mismatches between struct and class are also fixed. clang 2.8 is not working as it has problems with class names that occur in multiple namespaces (e.g. Statistics in kernel_stats.hh). clang has a bug (http://llvm.org/bugs/show_bug.cgi?id=7247) which causes confusion between the container std::set and the function Packet::set, and this is currently addressed by not including the entire namespace std, but rather selecting e.g. "using std::vector" in the appropriate places.
2011-09-27Faults: Add in generic faults that work like panics, warns, etc.Gabe Black
These faults take varargs to their constructors which they print into a string and pass to the M5DebugFault base class. They are basically faults wrapped around panics, faults, warns, and warnonce-es so that they happen only at commit.
2011-07-02ExecContext: Rename the readBytes/writeBytes functions to readMem and writeMem.Gabe Black
readBytes and writeBytes had the word "bytes" in their names because they accessed blobs of bytes. This distinguished them from the read and write functions which handled higher level data types. Because those functions don't exist any more, this change renames readBytes and writeBytes to more general names, readMem and writeMem, which reflect the fact that they are how you read and write memory. This also makes their names more consistent with the register reading/writing functions, although those are still read and set for some reason.
2011-07-02ISA: Use readBytes/writeBytes for all instruction level memory operations.Gabe Black
2011-06-28arch: print next upc correctlyNilay Vaish
The patch corrects the print statement which prints the current and the next pc. Instead of the next upc, the next pc was being printed.
2011-06-19cpus/isa: add a != operator for pcstateKorey Sewell
2011-06-02copyright: clean up copyright blocksNathan Binkert
2011-04-15includes: sort all includesNathan Binkert
2011-02-13X86: Define fault objects to carry debug messages.Gabe Black
These faults can panic/warn/warn_once, etc., instead of instructions doing that themselves directly. That way, instructions can be speculatively executed, and only if they're actually going to commit will their fault be invoked and the panic, etc., happen.
2010-10-31ISA,CPU,etc: Create an ISA defined PC type that abstracts out ISA behaviors.Gabe Black
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.