derek/gem5
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

arm: Clean up and document decoder API

Browse Source 
This changeset adds more documentation to the ArmISA::Decoder class
and restructures it slightly to make API groups more obvious.
This commit is contained in:
Andreas Sandberg
2014-12-23 09:31:17 -05:00
parent 070b4a81db
commit b33812ba43
2 changed files with 163 additions and 88 deletions
Download Patch File Download Diff File Expand all files Collapse all files

52
src/arch/arm/decoder.cc
View File

@@ -1,5 +1,5 @@
/*
* Copyright (c) 2012-2013 ARM Limited
* Copyright (c) 2012-2014 ARM Limited
* All rights reserved
*
* The license below extends only to copyright in the software and shall
@@ -51,6 +51,23 @@ namespace ArmISA
GenericISA::BasicDecodeCache Decoder::defaultCache;
Decoder::Decoder()
: data(0), fpscrLen(0), fpscrStride(0)
{
reset();
}
void
Decoder::reset()
{
bigThumb = false;
offset = 0;
emi = 0;
instDone = false;
outOfBytes = true;
foundIt = false;
}
void
Decoder::process()
{
@@ -118,8 +135,15 @@ Decoder::process()
}
}
//Use this to give data to the decoder. This should be used
//when there is control flow.
void
Decoder::consumeBytes(int numBytes)
{
offset += numBytes;
assert(offset <= sizeof(MachInst));
if (offset == sizeof(MachInst))
outOfBytes = true;
}
void
Decoder::moreBytes(const PCState &pc, Addr fetchPC, MachInst inst)
{
@@ -134,4 +158,26 @@ Decoder::moreBytes(const PCState &pc, Addr fetchPC, MachInst inst)
process();
}
StaticInstPtr
Decoder::decode(ArmISA::PCState &pc)
{
if (!instDone)
return NULL;
const int inst_size((!emi.thumb || emi.bigThumb) ? 4 : 2);
ExtMachInst this_emi(emi);
pc.npc(pc.pc() + inst_size);
if (foundIt)
pc.nextItstate(itBits);
this_emi.itstate = pc.itstate();
pc.size(inst_size);
emi = 0;
instDone = false;
foundIt = false;
return decode(this_emi, pc.instAddr());
}
}

199
src/arch/arm/decoder.hh
View File

@@ -1,5 +1,5 @@
/*
* Copyright (c) 2013 ARM Limited
* Copyright (c) 2013-2014 ARM Limited
* All rights reserved
*
* The license below extends only to copyright in the software and shall
@@ -70,99 +70,128 @@ class Decoder
int fpscrLen;
int fpscrStride;
public:
void reset()
{
bigThumb = false;
offset = 0;
emi = 0;
instDone = false;
outOfBytes = true;
foundIt = false;
}
Decoder() : data(0), fpscrLen(0), fpscrStride(0)
{
reset();
}
void process();
//Use this to give data to the decoder. This should be used
//when there is control flow.
void moreBytes(const PCState &pc, Addr fetchPC, MachInst inst);
//Use this to give data to the decoder. This should be used
//when instructions are executed in order.
void moreBytes(MachInst machInst)
{
moreBytes(0, 0, machInst);
}
inline void consumeBytes(int numBytes)
{
offset += numBytes;
assert(offset <= sizeof(MachInst));
if (offset == sizeof(MachInst))
outOfBytes = true;
}
bool needMoreBytes() const
{
return outOfBytes;
}
bool instReady() const
{
return instDone;
}
int getInstSize() const
{
return (!emi.thumb || emi.bigThumb) ? 4 : 2;
}
void setContext(FPSCR fpscr)
{
fpscrLen = fpscr.len;
fpscrStride = fpscr.stride;
}
void takeOverFrom(Decoder *old) {}
protected:
/// A cache of decoded instruction objects.
static GenericISA::BasicDecodeCache defaultCache;
public:
StaticInstPtr decodeInst(ExtMachInst mach_inst);
/**
* Pre-decode an instruction from the current state of the
* decoder.
*/
void process();
/// Decode a machine instruction.
/// @param mach_inst The binary instruction to decode.
/// @retval A pointer to the corresponding StaticInst object.
StaticInstPtr
decode(ExtMachInst mach_inst, Addr addr)
/**
* Consume bytes by moving the offset into the data word and
* sanity check the results.
*/
void consumeBytes(int numBytes);
public: // Decoder API
Decoder();
/** Reset the decoders internal state. */
void reset();
/**
* Can the decoder accept more data?
*
* A CPU model uses this method to determine if the decoder can
* accept more data. Note that an instruction can be ready (see
* instReady() even if this method returns true.
*/
bool needMoreBytes() const { return outOfBytes; }
/**
* Is an instruction ready to be decoded?
*
* CPU models call this method to determine if decode() will
* return a new instruction on the next call. It typically only
* returns false if the decoder hasn't received enough data to
* decode a full instruction.
*/
bool instReady() const { return instDone; }
/**
* Feed data to the decoder.
*
* A CPU model uses this interface to load instruction data into
* the decoder. Once enough data has been loaded (check with
* instReady()), a decoded instruction can be retrieved using
* decode(ArmISA::PCState).
*
* This method is intended to support both fixed-length and
* variable-length instructions. Instruction data is fetch in
* MachInst blocks (which correspond to the size of a typical
* insturction). The method might need to be called multiple times
* if the instruction spans multiple blocks, in that case
* needMoreBytes() will return true and instReady() will return
* false.
*
* The fetchPC parameter is used to indicate where in memory the
* instruction was fetched from. This is should be the same
* address as the pc. If fetching multiple blocks, it indicates
* where subsequent blocks are fetched from (pc + n *
* sizeof(MachInst)).
*
* @param pc Instruction pointer that we are decoding.
* @param fetchPC The address this chunk was fetched from.
* @param inst Raw instruction data.
*/
void moreBytes(const PCState &pc, Addr fetchPC, MachInst inst);
/**
* Decode an instruction or fetch it from the code cache.
*
* This method decodes the currently pending pre-decoded
* instruction. Data must be fed to the decoder using moreBytes()
* until instReady() is true before calling this method.
*
* @param pc Instruction pointer that we are decoding.
* @return A pointer to a static instruction or NULL if the
* decoder isn't ready (see instReady()).
*/
StaticInstPtr decode(ArmISA::PCState &pc);
/**
* Decode a pre-decoded machine instruction.
*
* @warn This method takes a pre-decoded instruction as its
* argument. It should typically not be called directly.
*
* @param mach_inst A pre-decoded instruction
* @retval A pointer to the corresponding StaticInst object.
*/
StaticInstPtr decode(ExtMachInst mach_inst, Addr addr)
{
return defaultCache.decode(this, mach_inst, addr);
}
StaticInstPtr
decode(ArmISA::PCState &nextPC)
{
if (!instDone)
return NULL;
/**
* Decode a machine instruction without calling the cache.
*
* @note The implementation of this method is generated by the ISA
* parser script.
*
* @warn This method takes a pre-decoded instruction as its
* argument. It should typically not be called directly.
*
* @param mach_inst The binary instruction to decode.
* @retval A pointer to the corresponding StaticInst object.
*/
StaticInstPtr decodeInst(ExtMachInst mach_inst);
assert(instDone);
ExtMachInst thisEmi = emi;
nextPC.npc(nextPC.pc() + getInstSize());
if (foundIt)
nextPC.nextItstate(itBits);
thisEmi.itstate = nextPC.itstate();
nextPC.size(getInstSize());
emi = 0;
instDone = false;
foundIt = false;
return decode(thisEmi, nextPC.instAddr());
/**
* Take over the state from an old decoder when switching CPUs.
*
* @param old Decoder used in old CPU
*/
void takeOverFrom(Decoder *old) {}
public: // ARM-specific decoder state manipulation
void setContext(FPSCR fpscr)
{
fpscrLen = fpscr.len;
fpscrStride = fpscr.stride;
}
};