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2018-06-22arch-arm: AArch32 execution triggering AArch64 SW BreakGiacomo Travaglini
AArch32 Software Breakpoint (BKPT) can trigger an AArch64 fault when interprocessing if the trapping conditions are met. Change-Id: I485852ed19429f9cd928a6447a95eb6f471f189c Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-on: https://gem5-review.googlesource.com/11197 Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2018-06-14arch-arm: Read APSR in User ModeGiacomo Travaglini
This patch substitutes reads to the CPSR in user mode (MRS CPSR) to reads to APSR (Application Program Status Register). This is the user level alias for the CPSR. The APSR is a subset of the CPSR. Change-Id: I18a70693aef6fd305a4c4cb3c6f81f331bc60a2d Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-on: https://gem5-review.googlesource.com/10602 Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2018-04-10arch-arm: Fix mrc,mcr to cop14 disassembleGiacomo Travaglini
This patch fixes the disassemble for AArch32 mcr/mrc p14 instructions. Change-Id: If5d7c2d7c726f040ae20053bf1d70f4405b34d0e Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Reviewed-by: Curtis Dunham <curtis.dunham@arm.com> Reviewed-on: https://gem5-review.googlesource.com/9681 Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2018-03-06arm: Remove ignored const qualifierSiddhesh Poyarekar
gcc8 warns about ignored const qualifiers (-Wignored-qualifiers) and that breaks builds. It was suggested that the warning be moved to Wextra[1] but that's probably not going to happen anytime soon. [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82711 Change-Id: Ib808906deb9a1c2dccb1c34b6563db0c24c66655 Signed-off-by: Siddhesh Poyarekar <siddhesh.poyarekar@gmail.com> Reviewed-on: https://gem5-review.googlesource.com/8562 Reviewed-by: Gabe Black <gabeblack@google.com> Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2018-02-20arch-arm: Add AArch32 HLT Semihosting interfaceGiacomo Travaglini
AArch32 HLT instruction is now able to issue Arm Semihosting commands as the AArch64 counterpart in either Arm and Thumb mode. Change-Id: I77da73d2e6a9288c704a5f646f4447022517ceb6 Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-on: https://gem5-review.googlesource.com/8372 Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2018-02-20arch-arm: Add AArch32 SVC Semihosting interfaceGiacomo Travaglini
AArch32 Svc instruction is now able to issue Arm Semihosting commands as the AArch64 counterpart in either Arm and Thumb mode. Change-Id: Ibe47ac23d0c26f3f819cc0e2b3ee874b5cdbb3d3 Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-on: https://gem5-review.googlesource.com/8371 Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2018-02-07arch-arm: Fix printing of the data cache maintenance instructionsNikos Nikoleris
Change-Id: I2322c7bf65b38cb07a1ea2b5dc25dfc5a0496cf0 Reviewed-by: Jack Travaglini <giacomo.travaglini@arm.com> Reviewed-on: https://gem5-review.googlesource.com/7825 Maintainer: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
2018-02-07arch-arm: Change function name for banked miscregsGiacomo Travaglini
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>
2018-02-07arch-arm: Fix AArch32 SETEND InstructionGiacomo Travaglini
This patch fixes AArch32 SETEND instruction, which was previously executed unconditionally without checking (H)SCTLR.SED field. This bit enables/disables the trapping of the instruction. Change-Id: Ib3d2194c8d16c34ec2a9ab3e8090081900c1e42e Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com> Reviewed-on: https://gem5-review.googlesource.com/7981 Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2018-02-05arch-arm: Removing Serializing flag from ISBGiacomo Travaglini
ISB Serializing behaviour is guaranteed by IsSquashAfter, which is inherently serializing; when instruction is commited, consecutive instructions are flushed and refetched. Change-Id: I05e61b4cf9f01113d95b1502c996d04cbd69b759 Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-on: https://gem5-review.googlesource.com/5701 Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2017-12-21arch-arm: Fixed WFE/WFI trapping behaviourGiacomo Travaglini
This patch fixes the WFx trapping behaviour by introducing the arm arm v8 pseudocode functions: checkForWFxTrap32 and checkForWFxTrap64 Change-Id: I3db0d78b5c4ad46860e6d199c2f2fc7b41842840 Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-on: https://gem5-review.googlesource.com/6622 Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2017-12-05arm: Add support for the mcr dc{ic,i,c}mvac, dccmvau instructionsNikos Nikoleris
This patch adds support for the ARMv7 cache maintenance intructions: * mcr dccmvac cleans a VA to the PoC * mcr dcimvac invalidates a VA to the PoC * mcr dccimvac cleans and invalidates a VA to the PoC * mcr dccmvau cleans a VA to the PoU Change-Id: I6511f203039ca145cc9128ddf61d09d6d7e40c10 Reviewed-by: Stephan Diestelhorst <stephan.diestelhorst@arm.com> Reviewed-by: Anouk Van Laer <anouk.vanlaer@arm.com> Reviewed-on: https://gem5-review.googlesource.com/5059 Maintainer: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
2017-11-15arch-arm: Dsb instruction shouldn't flush the pipelineGiacomo Travaglini
DSB Instruction shouldn't flush the pipeline, hence the IsSquashAfter attribute will be removed for either the 32 and 64 bit version. Change-Id: I98b2b8bc78aa28445ed1a9b5f34645f8d71616ad Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Reviewed-by: Giacomo Gabrielli <giacomo.gabrielli@arm.com> Reviewed-on: https://gem5-review.googlesource.com/5363 Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2017-11-15arch-arm: Removing FlushPipe fault, using SquashAfterGiacomo Travaglini
This Patch is removing the FlushPipe ArmFault, which was used for flushing the pipeline in favour of the general IsSquashAfter StaticInstr flag. Using a fault was preventing tracers from tracing barriers like ISB and from adding them to the instruction count Change-Id: I176e9254eca904694f2f611eb486c55e50ec61ff Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Reviewed-by: Giacomo Gabrielli <giacomo.gabrielli@arm.com> Reviewed-on: https://gem5-review.googlesource.com/5361 Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2017-11-15arm: Add support for armv8 CRC32 instructionsGiacomo Travaglini
This patch introduces the ARM A32/T32/A64 CRC Instructions, which are mandatory since ARMv8.1. The UNPREDICTABLE behaviours are implemented as follows: 1) CRC32(C)X (64 bit) instructions are decoded as Undefined in Aarch32 2) The instructions support predication in Aarch32 3) Using R15(PC) as source/dest operand is permitted in Aarch32 Change-Id: Iaf29b05874e1370c7615da79a07f111ded17b6cc Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com> Reviewed-by: Giacomo Gabrielli <giacomo.gabrielli@arm.com> Reviewed-on: https://gem5-review.googlesource.com/5521 Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
2017-10-20arch-arm: RBIT instruction using mirroring funcGiacomo Travaglini
The high speed bit-reversing function is now used for the Aarch64/32 RBIT instruction implementation. Change-Id: Id5a8a93d928d00fd33ec4061fbb586b8420a1c1b Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com> Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com> Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-on: https://gem5-review.googlesource.com/5262 Reviewed-by: Jason Lowe-Power <jason@lowepower.com> Maintainer: Jason Lowe-Power <jason@lowepower.com>
2017-07-05cpu: Simplify the rename interface and use RegIdRekai Gonzalez-Alberquilla
With the hierarchical RegId there are a lot of functions that are redundant now. The idea behind the simplification is that instead of having the regId, telling which kind of register read/write/rename/lookup/etc. and then the function panic_if'ing if the regId is not of the appropriate type, we provide an interface that decides what kind of register to read depending on the register type of the given regId. Change-Id: I7d52e9e21fc01205ae365d86921a4ceb67a57178 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/2702
2017-04-03arm: Don't panic when checking coprocessor read/write permissionsNikos Nikoleris
Instructions that use the coprocessor interface check the current program status to determine whether the current context has the priviledges to read from/write to the coprocessor. Some modes allow the execution of coprocessor instructions, some others do not allow it, while some other modes are unexpected (e.g., executing an AArch32 instruction while being in an AArch64 mode). Previously we would unconditionally trigger a panic if we were in an unexpected mode. This change removes the panic and replaces it with an Undefined Instruction fault that triggers if and when a coprocessor instruction commits in an unexpected mode. This allows speculative coprocessor instructions from unexpected modes to execute but prevents them from gettting committed. Change-Id: If2776d5bae2471cdbaf76d0e1ae655f501bfbf01 Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-by: Rekai Gonzalez Alberquilla <rekai.gonzalezalberquilla@arm.com> Reviewed-on: https://gem5-review.googlesource.com/2281 Maintainer: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-by: Weiping Liao <weipingliao@google.com>
2016-02-29arm: Squash after returning from exceptions in v7Mitch Hayenga
Properly done for the ERET instruction in v8, but not for v7. Many control register changes are only visible after explicit instruction synchronization barriers or exception entry/exit. This means mode changing instructions should squash any younger in-flight speculative instructions.
2015-09-30isa,cpu: Add support for FS SMT InterruptsMitch Hayenga
Adds per-thread interrupt controllers and thread/context logic so that interrupts properly get routed in SMT systems.
2014-09-02arm: Don't speculatively access most miscregisters.Akash Bagdia
Speculative exeuction can cause panics in detailed execution mode that shouldn't happen.
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".
2014-09-27arm: Fixed undefined behaviours identified by gccAndreas Hansson
This patch fixes the runtime errors highlighted by the undefined behaviour sanitizer. In the end there were two issues. First, when rotating an immediate, we ended up shifting an uint32_t by 32 in some cases. This case is fixed by checking for a rotation by 0 positions. Second, the Mrc15 and Mcr15 are operating on an IntReg and a MiscReg, but we used the type RegRegImmOp and passed a MiscRegIndex as an IntRegIndex. This issue is resolved by introducing a MiscRegRegImmOp and RegMiscRegImmOp with the appropriate types. With these fixes there are no runtime errors identified for the full ARM regressions.
2014-05-09arm: Panics in miscreg read functions can be tripped by O3 modelGeoffrey Blake
Unimplemented miscregs for the generic timer were guarded by panics in arm/isa.cc which can be tripped by the O3 model if it speculatively executes a wrong path containing a mrs instruction with a bad miscreg index. These registers were flagged as implemented and accessible. This patch changes the miscreg info bit vector to flag them as unimplemented and inaccessible. In this case, and UndefinedInst fault will be generated if the register access is not trapped by a hypervisor.
2014-01-24arm: Add support for ARMv8 (AArch64 & AArch32)ARM gem5 Developers
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
2012-03-21ARM: IT doesn't need to be serializing.Geoffrey Blake
2012-03-01ARM: Add limited CP14 support.Matt Horsnell
New kernels attempt to read CP14 what debug architecture is available. These changes add the debug registers and return that none is currently available.
2012-01-31Merge with head, hopefully the last time for this batch.Gabe Black
2012-01-31CheckerCPU: Re-factor CheckerCPU to be compatible with current gem5Geoffrey Blake
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.
2012-01-07Merge with the main repository again.Gabe Black
2011-12-01ARM: Add IsSerializeAfter and IsNonSpeculative flag to the syscall instruction .Ali Saidi
Squashes the subsequent instructions in O3 pipe after the service call, so that they see the effect of the system call when re-executed. This isn't really an issue with FS mode, but can show up in SE mode. --HG-- extra : rebase_source : 613a69fe1d9834261e25a8cd340aa6b47578e1fe
2011-11-02SE/FS: Get rid of FULL_SYSTEM in the ARM ISA.Gabe Black
2011-09-26ISA parser: Use '_' instead of '.' to delimit type modifiers on operands.Gabe Black
By using an underscore, the "." is still available and can unambiguously be used to refer to members of a structure if an operand is a structure, class, etc. This change mostly just replaces the appropriate "."s with "_"s, but there were also a few places where the ISA descriptions where handling the extensions themselves and had their own regular expressions to update. The regular expressions in the isa parser were updated as well. It also now looks for one of the defined type extensions specifically after connecting "_" where before it would look for any sequence of characters after a "." following an operand name and try to use it as the extension. This helps to disambiguate cases where a "_" may legitimately be part of an operand name but not separate the name from the type suffix. Because leaving the "_" and suffix on the variable name still leaves a valid C++ identifier and all extensions need to be consistent in a given context, I considered leaving them on as a breadcrumb that would show what the intended type was for that operand. Unfortunately the operands can be referred to in code templates, the Mem operand in particular, and since the exact type of Mem can be different for different uses of the same template, that broke things.
2011-08-19Fix bugs due to interaction between SEV instructions and O3 pipelineGeoffrey Blake
SEV instructions were originally implemented to cause asynchronous squashes via the generateTCSquash() function in the O3 pipeline when updating the SEV_MAILBOX miscReg. This caused race conditions between CPUs in an MP system that would lead to a pipeline either going inactive indefinitely or not being able to commit squashed instructions. Fixed SEV instructions to behave like interrupts and cause synchronous sqaushes inside the pipeline, eliminating the race conditions. Also fixed up the semantics of the WFE instruction to behave as documented in the ARMv7 ISA description to not sleep if SEV_MAILBOX=1 or unmasked interrupts are pending.
2011-05-13ARM: Construct the predicate test register for more instruction programatically.Ali Saidi
If one of the condition codes isn't being used in the execution we should only read it if the instruction might be dependent on it. With the preeceding changes there are several more cases where we should dynamically pick instead of assuming as we did before.
2011-05-13ARM: Further break up condition code into NZ, C, V bits.Ali Saidi
Break up the condition code bits into NZ, C, V registers. These are individually written and this removes some incorrect dependencies between instructions.
2011-05-13ARM: Remove the saturating (Q) condition code from the renamed register.Ali Saidi
Move the saturating bit (which is also saturating) from the renamed register that holds the flags to the CPSR miscreg and adds a allows setting it in a similar way to the FP saturating registers. This removes a dependency in instructions that don't write, but need to preserve the Q bit.
2011-05-13ARM: Break up condition codes into normal flags, saturation, and simd.Ali Saidi
This change splits out the condcodes from being one monolithic register into three blocks that are updated independently. This allows CPUs to not have to do RMW operations on the flags registers for instructions that don't write all flags.
2011-05-04ARM: Implement WFE/WFI/SEV semantics.Prakash Ramrakhyani
2011-04-04ARM: Use CPU local lock before sending load to mem system.Ali Saidi
This change uses the locked_mem.hh header to handle implementing CLREX. It simplifies the current implementation greatly.
2011-04-04ARM: Cleanup implementation of ITSTATE and put important code in PCState.Ali Saidi
Consolidate all code to handle ITSTATE in the PCState object rather than touching a variety of structures/objects.
2011-03-17ARM: Allow conditional quiesce instructions.Ali Saidi
This patch prevents not executed conditional instructions marked as IsQuiesce from stalling the pipeline indefinitely. If the instruction is not executed the quiesceSkip psuedoinst is called which schedules a wakes up call to the fetch stage.
2011-02-23ARM: Do something for ISB, DSB, DMBAli Saidi
2011-02-23ARM: Make Noop actually decode to a noop and set it's instflags.Ali Saidi
2011-01-18O3: Fix itstate prediction and recovery.Matt Horsnell
Any change of control flow now resets the itstate to 0 mask and 0 condition, except where the control flow alteration write into the cpsr register. These case, for example return from an iterrupt, require the predecoder to recover the itstate. As there is a window of opportunity between the return from an interrupt changing the control flow at the head of the pipe and the commit of the update to the CPSR, the predecoder needs to be able to grab the ITstate early. This is now handled by setting the forcedItState inside a PCstate for the control flow altering instruction. That instruction will have the correct mask/cond, but will not have a valid itstate until advancePC is called (note this happens to advance the execution). When the new PCstate is copy constructed it gets the itstate cond/mask, and upon advancing the PC the itstate becomes valid. Subsequent advancing invalidates the state and zeroes the cond/mask. This is handled in isolation for the ARM ISA and should have no impact on other ISAs. Refer arch/arm/types.hh and arch/arm/predecoder.cc for the details.
2011-01-18ARM: Add support for moving predicated false dest operands from sources.Ali Saidi
2010-12-09ARM: Take advantage of new PCState syntax.Gabe Black
2010-12-07O3: Make all instructions that write a misc. register not perform the write ↵Giacomo Gabrielli
until commit. ARM instructions updating cumulative flags (ARM FP exceptions and saturation flags) are not serialized. Added aliases for ARM FP exceptions and saturation flags in FPSCR. Removed write accesses to the FP condition codes for most ARM VFP instructions: only VCMP and VCMPE instructions update the FP condition codes. Removed a potential cause of seg. faults in the O3 model for NEON memory macro-ops (ARM).
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.
2010-10-13Mem: Change the CLREX flag to CLEAR_LL.Gabe Black
CLREX is the name of an ARM instruction, not a name for this generic flag.