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|
// -*- mode:c++ -*-
////////////////////////////////////////////////////////////////////
//
// Control transfer instructions
//
output header {{
/**
* Base class for instructions whose disassembly is not purely a
* function of the machine instruction (i.e., it depends on the
* PC). This class overrides the disassemble() method to check
* the PC and symbol table values before re-using a cached
* disassembly string. This is necessary for branches and jumps,
* where the disassembly string includes the target address (which
* may depend on the PC and/or symbol table).
*/
class PCDependentDisassembly : public MipsStaticInst
{
protected:
/// Cached program counter from last disassembly
mutable Addr cachedPC;
/// Cached symbol table pointer from last disassembly
mutable const SymbolTable *cachedSymtab;
/// Constructor
PCDependentDisassembly(const char *mnem, MachInst _machInst,
OpClass __opClass)
: MipsStaticInst(mnem, _machInst, __opClass),
cachedPC(0), cachedSymtab(0)
{
}
const std::string &
disassemble(Addr pc, const SymbolTable *symtab) const;
};
/**
* Base class for branches (PC-relative control transfers),
* conditional or unconditional.
*/
class Branch : public PCDependentDisassembly
{
protected:
/// target address (signed) Displacement .
int32_t targetOffset;
/// Constructor.
Branch(const char *mnem, MachInst _machInst, OpClass __opClass)
: PCDependentDisassembly(mnem, _machInst, __opClass),
targetOffset(OFFSET << 2)
{
}
Addr branchTarget(Addr branchPC) const;
std::string
generateDisassembly(Addr pc, const SymbolTable *symtab) const;
};
/**
* Base class for branches (PC-relative control transfers),
* conditional or unconditional.
*/
class BranchLikely : public PCDependentDisassembly
{
protected:
/// target address (signed) Displacement .
int32_t targetOffset;
/// Constructor.
Branch(const char *mnem, MachInst _machInst, OpClass __opClass)
: PCDependentDisassembly(mnem, _machInst, __opClass),
targetOffset(OFFSET << 2)
{
}
Addr branchTarget(Addr branchPC) const;
std::string
generateDisassembly(Addr pc, const SymbolTable *symtab) const;
};
/**
* Base class for jumps (register-indirect control transfers). In
* the Mips ISA, these are always unconditional.
*/
class Jump : public PCDependentDisassembly
{
protected:
/// Displacement to target address (signed).
int32_t disp;
public:
/// Constructor
Jump(const char *mnem, MachInst _machInst, OpClass __opClass)
: PCDependentDisassembly(mnem, _machInst, __opClass),
disp(OFFSET)
{
}
Addr branchTarget(ExecContext *xc) const;
std::string
generateDisassembly(Addr pc, const SymbolTable *symtab) const;
};
}};
output decoder {{
Addr
Branch::branchTarget(Addr branchPC) const
{
return branchPC + 4 + disp;
}
Addr
Jump::branchTarget(ExecContext *xc) const
{
Addr NPC = xc->readPC() + 4;
uint64_t Rb = xc->readIntReg(_srcRegIdx[0]);
return (Rb & ~3) | (NPC & 1);
}
const std::string &
PCDependentDisassembly::disassemble(Addr pc,
const SymbolTable *symtab) const
{
if (!cachedDisassembly ||
pc != cachedPC || symtab != cachedSymtab)
{
if (cachedDisassembly)
delete cachedDisassembly;
cachedDisassembly =
new std::string(generateDisassembly(pc, symtab));
cachedPC = pc;
cachedSymtab = symtab;
}
return *cachedDisassembly;
}
std::string
Branch::generateDisassembly(Addr pc, const SymbolTable *symtab) const
{
std::stringstream ss;
ccprintf(ss, "%-10s ", mnemonic);
// There's only one register arg (RA), but it could be
// either a source (the condition for conditional
// branches) or a destination (the link reg for
// unconditional branches)
if (_numSrcRegs > 0) {
printReg(ss, _srcRegIdx[0]);
ss << ",";
}
else if (_numDestRegs > 0) {
printReg(ss, _destRegIdx[0]);
ss << ",";
}
#ifdef SS_COMPATIBLE_DISASSEMBLY
if (_numSrcRegs == 0 && _numDestRegs == 0) {
printReg(ss, 31);
ss << ",";
}
#endif
Addr target = pc + 4 + disp;
std::string str;
if (symtab && symtab->findSymbol(target, str))
ss << str;
else
ccprintf(ss, "0x%x", target);
return ss.str();
}
std::string
Jump::generateDisassembly(Addr pc, const SymbolTable *symtab) const
{
std::stringstream ss;
ccprintf(ss, "%-10s ", mnemonic);
#ifdef SS_COMPATIBLE_DISASSEMBLY
if (_numDestRegs == 0) {
printReg(ss, 31);
ss << ",";
}
#endif
if (_numDestRegs > 0) {
printReg(ss, _destRegIdx[0]);
ss << ",";
}
ccprintf(ss, "(r%d)", RB);
return ss.str();
}
}};
def template JumpOrBranchDecode {{
return (RD == 0)
? (StaticInst<MipsISA> *)new %(class_name)s(machInst)
: (StaticInst<MipsISA> *)new %(class_name)sAndLink(machInst);
}};
def format Branch(code) {{
code = 'bool cond;\n' + code + '\nif (cond) NPC = NPC + disp;\n';
iop = InstObjParams(name, Name, 'Branch', CodeBlock(code),
('IsDirectControl', 'IsCondControl'))
header_output = BasicDeclare.subst(iop)
decoder_output = BasicConstructor.subst(iop)
decode_block = BasicDecode.subst(iop)
exec_output = BasicExecute.subst(iop)
}};
def format BranchLikely(code) {{
code = 'bool cond;\n' + code + '\nif (cond) NPC = NPC + disp;\n';
iop = InstObjParams(name, Name, 'Branch', CodeBlock(code),
('IsDirectControl', 'IsCondControl'))
header_output = BasicDeclare.subst(iop)
decoder_output = BasicConstructor.subst(iop)
decode_block = BasicDecode.subst(iop)
exec_output = BasicExecute.subst(iop)
}};
def format UncondBranch(*flags) {{
flags += ('IsUncondControl', 'IsDirectControl')
(header_output, decoder_output, decode_block, exec_output) = \
UncondCtrlBase(name, Name, 'Branch', 'NPC + disp', flags)
}};
def format Jump(*flags) {{
flags += ('IsUncondControl', 'IsIndirectControl')
(header_output, decoder_output, decode_block, exec_output) = \
UncondCtrlBase(name, Name, 'Jump', '(Rb & ~3) | (NPC & 1)', flags)
}};
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