Files
gem5/src/cpu/simple_thread.hh
Brandon Potter a5802c823f syscall_emul: [patch 13/22] add system call retry capability
This changeset adds functionality that allows system calls to retry without
affecting thread context state such as the program counter or register values
for the associated thread context (when system calls return with a retry
fault).

This functionality is needed to solve problems with blocking system calls
in multi-process or multi-threaded simulations where information is passed
between processes/threads. Blocking system calls can cause deadlock because
the simulator itself is single threaded. There is only a single thread
servicing the event queue which can cause deadlock if the thread hits a
blocking system call instruction.

To illustrate the problem, consider two processes using the producer/consumer
sharing model. The processes can use file descriptors and the read and write
calls to pass information to one another. If the consumer calls the blocking
read system call before the producer has produced anything, the call will
block the event queue (while executing the system call instruction) and
deadlock the simulation.

The solution implemented in this changeset is to recognize that the system
calls will block and then generate a special retry fault. The fault will
be sent back up through the function call chain until it is exposed to the
cpu model's pipeline where the fault becomes visible. The fault will trigger
the cpu model to replay the instruction at a future tick where the call has
a chance to succeed without actually going into a blocking state.

In subsequent patches, we recognize that a syscall will block by calling a
non-blocking poll (from inside the system call implementation) and checking
for events. When events show up during the poll, it signifies that the call
would not have blocked and the syscall is allowed to proceed (calling an
underlying host system call if necessary). If no events are returned from the
poll, we generate the fault and try the instruction for the thread context
at a distant tick. Note that retrying every tick is not efficient.

As an aside, the simulator has some multi-threading support for the event
queue, but it is not used by default and needs work. Even if the event queue
was completely multi-threaded, meaning that there is a hardware thread on
the host servicing a single simulator thread contexts with a 1:1 mapping
between them, it's still possible to run into deadlock due to the event queue
barriers on quantum boundaries. The solution of replaying at a later tick
is the simplest solution and solves the problem generally.
2015-07-20 09:15:21 -05:00

457 lines
13 KiB
C++

/*
* Copyright (c) 2011-2012 ARM Limited
* Copyright (c) 2013 Advanced Micro Devices, Inc.
* All rights reserved
*
* The license below extends only to copyright in the software and shall
* not be construed as granting a license to any other intellectual
* property including but not limited to intellectual property relating
* to a hardware implementation of the functionality of the software
* licensed hereunder. You may use the software subject to the license
* terms below provided that you ensure that this notice is replicated
* unmodified and in its entirety in all distributions of the software,
* modified or unmodified, in source code or in binary form.
*
* Copyright (c) 2001-2006 The Regents of The University of Michigan
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: Steve Reinhardt
* Nathan Binkert
*/
#ifndef __CPU_SIMPLE_THREAD_HH__
#define __CPU_SIMPLE_THREAD_HH__
#include "arch/decoder.hh"
#include "arch/isa.hh"
#include "arch/isa_traits.hh"
#include "arch/registers.hh"
#include "arch/tlb.hh"
#include "arch/types.hh"
#include "base/types.hh"
#include "config/the_isa.hh"
#include "cpu/thread_context.hh"
#include "cpu/thread_state.hh"
#include "debug/CCRegs.hh"
#include "debug/FloatRegs.hh"
#include "debug/IntRegs.hh"
#include "mem/page_table.hh"
#include "mem/request.hh"
#include "sim/byteswap.hh"
#include "sim/eventq.hh"
#include "sim/process.hh"
#include "sim/serialize.hh"
#include "sim/system.hh"
class BaseCPU;
class CheckerCPU;
class FunctionProfile;
class ProfileNode;
namespace TheISA {
namespace Kernel {
class Statistics;
}
}
/**
* The SimpleThread object provides a combination of the ThreadState
* object and the ThreadContext interface. It implements the
* ThreadContext interface so that a ProxyThreadContext class can be
* made using SimpleThread as the template parameter (see
* thread_context.hh). It adds to the ThreadState object by adding all
* the objects needed for simple functional execution, including a
* simple architectural register file, and pointers to the ITB and DTB
* in full system mode. For CPU models that do not need more advanced
* ways to hold state (i.e. a separate physical register file, or
* separate fetch and commit PC's), this SimpleThread class provides
* all the necessary state for full architecture-level functional
* simulation. See the AtomicSimpleCPU or TimingSimpleCPU for
* examples.
*/
class SimpleThread : public ThreadState
{
protected:
typedef TheISA::MachInst MachInst;
typedef TheISA::MiscReg MiscReg;
typedef TheISA::FloatReg FloatReg;
typedef TheISA::FloatRegBits FloatRegBits;
typedef TheISA::CCReg CCReg;
public:
typedef ThreadContext::Status Status;
protected:
union {
FloatReg f[TheISA::NumFloatRegs];
FloatRegBits i[TheISA::NumFloatRegs];
} floatRegs;
TheISA::IntReg intRegs[TheISA::NumIntRegs];
#ifdef ISA_HAS_CC_REGS
TheISA::CCReg ccRegs[TheISA::NumCCRegs];
#endif
TheISA::ISA *const isa; // one "instance" of the current ISA.
TheISA::PCState _pcState;
/** Did this instruction execute or is it predicated false */
bool predicate;
public:
std::string name() const
{
return csprintf("%s.[tid:%i]", baseCpu->name(), tc->threadId());
}
ProxyThreadContext<SimpleThread> *tc;
System *system;
TheISA::TLB *itb;
TheISA::TLB *dtb;
TheISA::Decoder decoder;
// constructor: initialize SimpleThread from given process structure
// FS
SimpleThread(BaseCPU *_cpu, int _thread_num, System *_system,
TheISA::TLB *_itb, TheISA::TLB *_dtb, TheISA::ISA *_isa,
bool use_kernel_stats = true);
// SE
SimpleThread(BaseCPU *_cpu, int _thread_num, System *_system,
Process *_process, TheISA::TLB *_itb, TheISA::TLB *_dtb,
TheISA::ISA *_isa);
virtual ~SimpleThread();
virtual void takeOverFrom(ThreadContext *oldContext);
void regStats(const std::string &name);
void copyState(ThreadContext *oldContext);
void serialize(CheckpointOut &cp) const override;
void unserialize(CheckpointIn &cp) override;
void startup();
/***************************************************************
* SimpleThread functions to provide CPU with access to various
* state.
**************************************************************/
/** Returns the pointer to this SimpleThread's ThreadContext. Used
* when a ThreadContext must be passed to objects outside of the
* CPU.
*/
ThreadContext *getTC() { return tc; }
void demapPage(Addr vaddr, uint64_t asn)
{
itb->demapPage(vaddr, asn);
dtb->demapPage(vaddr, asn);
}
void demapInstPage(Addr vaddr, uint64_t asn)
{
itb->demapPage(vaddr, asn);
}
void demapDataPage(Addr vaddr, uint64_t asn)
{
dtb->demapPage(vaddr, asn);
}
void dumpFuncProfile();
Fault hwrei();
bool simPalCheck(int palFunc);
/*******************************************
* ThreadContext interface functions.
******************************************/
BaseCPU *getCpuPtr() { return baseCpu; }
TheISA::TLB *getITBPtr() { return itb; }
TheISA::TLB *getDTBPtr() { return dtb; }
CheckerCPU *getCheckerCpuPtr() { return NULL; }
TheISA::Decoder *getDecoderPtr() { return &decoder; }
System *getSystemPtr() { return system; }
Status status() const { return _status; }
void setStatus(Status newStatus) { _status = newStatus; }
/// Set the status to Active.
void activate();
/// Set the status to Suspended.
void suspend();
/// Set the status to Halted.
void halt();
void copyArchRegs(ThreadContext *tc);
void clearArchRegs()
{
_pcState = 0;
memset(intRegs, 0, sizeof(intRegs));
memset(floatRegs.i, 0, sizeof(floatRegs.i));
#ifdef ISA_HAS_CC_REGS
memset(ccRegs, 0, sizeof(ccRegs));
#endif
isa->clear();
}
//
// New accessors for new decoder.
//
uint64_t readIntReg(int reg_idx)
{
int flatIndex = isa->flattenIntIndex(reg_idx);
assert(flatIndex < TheISA::NumIntRegs);
uint64_t regVal(readIntRegFlat(flatIndex));
DPRINTF(IntRegs, "Reading int reg %d (%d) as %#x.\n",
reg_idx, flatIndex, regVal);
return regVal;
}
FloatReg readFloatReg(int reg_idx)
{
int flatIndex = isa->flattenFloatIndex(reg_idx);
assert(flatIndex < TheISA::NumFloatRegs);
FloatReg regVal(readFloatRegFlat(flatIndex));
DPRINTF(FloatRegs, "Reading float reg %d (%d) as %f, %#x.\n",
reg_idx, flatIndex, regVal, floatRegs.i[flatIndex]);
return regVal;
}
FloatRegBits readFloatRegBits(int reg_idx)
{
int flatIndex = isa->flattenFloatIndex(reg_idx);
assert(flatIndex < TheISA::NumFloatRegs);
FloatRegBits regVal(readFloatRegBitsFlat(flatIndex));
DPRINTF(FloatRegs, "Reading float reg %d (%d) bits as %#x, %f.\n",
reg_idx, flatIndex, regVal, floatRegs.f[flatIndex]);
return regVal;
}
CCReg readCCReg(int reg_idx)
{
#ifdef ISA_HAS_CC_REGS
int flatIndex = isa->flattenCCIndex(reg_idx);
assert(0 <= flatIndex);
assert(flatIndex < TheISA::NumCCRegs);
uint64_t regVal(readCCRegFlat(flatIndex));
DPRINTF(CCRegs, "Reading CC reg %d (%d) as %#x.\n",
reg_idx, flatIndex, regVal);
return regVal;
#else
panic("Tried to read a CC register.");
return 0;
#endif
}
void setIntReg(int reg_idx, uint64_t val)
{
int flatIndex = isa->flattenIntIndex(reg_idx);
assert(flatIndex < TheISA::NumIntRegs);
DPRINTF(IntRegs, "Setting int reg %d (%d) to %#x.\n",
reg_idx, flatIndex, val);
setIntRegFlat(flatIndex, val);
}
void setFloatReg(int reg_idx, FloatReg val)
{
int flatIndex = isa->flattenFloatIndex(reg_idx);
assert(flatIndex < TheISA::NumFloatRegs);
setFloatRegFlat(flatIndex, val);
DPRINTF(FloatRegs, "Setting float reg %d (%d) to %f, %#x.\n",
reg_idx, flatIndex, val, floatRegs.i[flatIndex]);
}
void setFloatRegBits(int reg_idx, FloatRegBits val)
{
int flatIndex = isa->flattenFloatIndex(reg_idx);
assert(flatIndex < TheISA::NumFloatRegs);
// XXX: Fix array out of bounds compiler error for gem5.fast
// when checkercpu enabled
if (flatIndex < TheISA::NumFloatRegs)
setFloatRegBitsFlat(flatIndex, val);
DPRINTF(FloatRegs, "Setting float reg %d (%d) bits to %#x, %#f.\n",
reg_idx, flatIndex, val, floatRegs.f[flatIndex]);
}
void setCCReg(int reg_idx, CCReg val)
{
#ifdef ISA_HAS_CC_REGS
int flatIndex = isa->flattenCCIndex(reg_idx);
assert(flatIndex < TheISA::NumCCRegs);
DPRINTF(CCRegs, "Setting CC reg %d (%d) to %#x.\n",
reg_idx, flatIndex, val);
setCCRegFlat(flatIndex, val);
#else
panic("Tried to set a CC register.");
#endif
}
TheISA::PCState
pcState()
{
return _pcState;
}
void
pcState(const TheISA::PCState &val)
{
_pcState = val;
}
void
pcStateNoRecord(const TheISA::PCState &val)
{
_pcState = val;
}
Addr
instAddr()
{
return _pcState.instAddr();
}
Addr
nextInstAddr()
{
return _pcState.nextInstAddr();
}
MicroPC
microPC()
{
return _pcState.microPC();
}
bool readPredicate()
{
return predicate;
}
void setPredicate(bool val)
{
predicate = val;
}
MiscReg
readMiscRegNoEffect(int misc_reg, ThreadID tid = 0) const
{
return isa->readMiscRegNoEffect(misc_reg);
}
MiscReg
readMiscReg(int misc_reg, ThreadID tid = 0)
{
return isa->readMiscReg(misc_reg, tc);
}
void
setMiscRegNoEffect(int misc_reg, const MiscReg &val, ThreadID tid = 0)
{
return isa->setMiscRegNoEffect(misc_reg, val);
}
void
setMiscReg(int misc_reg, const MiscReg &val, ThreadID tid = 0)
{
return isa->setMiscReg(misc_reg, val, tc);
}
int
flattenIntIndex(int reg)
{
return isa->flattenIntIndex(reg);
}
int
flattenFloatIndex(int reg)
{
return isa->flattenFloatIndex(reg);
}
int
flattenCCIndex(int reg)
{
return isa->flattenCCIndex(reg);
}
int
flattenMiscIndex(int reg)
{
return isa->flattenMiscIndex(reg);
}
unsigned readStCondFailures() { return storeCondFailures; }
void setStCondFailures(unsigned sc_failures)
{ storeCondFailures = sc_failures; }
void syscall(int64_t callnum, Fault *fault)
{
process->syscall(callnum, tc, fault);
}
uint64_t readIntRegFlat(int idx) { return intRegs[idx]; }
void setIntRegFlat(int idx, uint64_t val) { intRegs[idx] = val; }
FloatReg readFloatRegFlat(int idx) { return floatRegs.f[idx]; }
void setFloatRegFlat(int idx, FloatReg val) { floatRegs.f[idx] = val; }
FloatRegBits readFloatRegBitsFlat(int idx) { return floatRegs.i[idx]; }
void setFloatRegBitsFlat(int idx, FloatRegBits val) {
floatRegs.i[idx] = val;
}
#ifdef ISA_HAS_CC_REGS
CCReg readCCRegFlat(int idx) { return ccRegs[idx]; }
void setCCRegFlat(int idx, CCReg val) { ccRegs[idx] = val; }
#else
CCReg readCCRegFlat(int idx)
{ panic("readCCRegFlat w/no CC regs!\n"); }
void setCCRegFlat(int idx, CCReg val)
{ panic("setCCRegFlat w/no CC regs!\n"); }
#endif
};
#endif // __CPU_CPU_EXEC_CONTEXT_HH__