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LibX86: Add a templatized way to resolve ModR/M memory references

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Hopefully this will be flexible enough for our SoftCPU. :^)
This commit is contained in:
Andreas Kling 2020-07-10 16:23:07 +02:00
parent 3a1cf9505d
commit 45bfdd0063
1 changed files with 215 additions and 6 deletions
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221
Libraries/LibX86/Instruction.h
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@ -204,12 +204,11 @@ public:
RegisterIndex16 reg16() const { return static_cast<RegisterIndex16>(register_index()); }
RegisterIndex8 reg8() const { return static_cast<RegisterIndex8>(register_index()); }
SegmentRegister segment() const
{
ASSERT(!is_register());
return m_segment;
}
u32 offset();
template<typename CPU>
void write32(CPU&, const Instruction&, u32);
template<typename CPU>
u32 read32(CPU&, const Instruction&);
private:
MemoryOrRegisterReference() { }
@ -222,6 +221,14 @@ private:
void decode16(InstructionStream&);
void decode32(InstructionStream&);
template<typename CPU>
LogicalAddress resolve16(const CPU&, Optional<SegmentRegister>);
template<typename CPU>
LogicalAddress resolve32(const CPU&, Optional<SegmentRegister>);
template<typename CPU>
u32 evaluate_sib(const CPU&, SegmentRegister& default_segment) const;
unsigned m_register_index { 0xffffffff };
SegmentRegister m_segment;
union {
@ -372,4 +379,206 @@ private:
InstructionDescriptor* m_descriptor { nullptr };
};
template<typename CPU>
LogicalAddress MemoryOrRegisterReference::resolve16(const CPU& cpu, Optional<SegmentRegister> segment_prefix)
{
ASSERT(!m_a32);
auto default_segment = SegmentRegister::DS;
u16 offset = 0;
switch (m_rm & 7) {
case 0:
offset = cpu.bx() + cpu.si() + m_displacement16;
break;
case 1:
offset = cpu.bx() + cpu.di() + m_displacement16;
break;
case 2:
default_segment = SegmentRegister::SS;
offset = cpu.bp() + cpu.si() + m_displacement16;
break;
case 3:
default_segment = SegmentRegister::SS;
offset = cpu.bp() + cpu.di() + m_displacement16;
break;
case 4:
offset = cpu.si() + m_displacement16;
break;
case 5:
offset = cpu.di() + m_displacement16;
break;
case 6:
if ((m_rm & 0xc0) == 0)
offset = m_displacement16;
else {
default_segment = SegmentRegister::SS;
offset = cpu.bp() + m_displacement16;
}
break;
default:
offset = cpu.bx() + m_displacement16;
break;
}
u16 segment = cpu.segment(segment_prefix.value_or(default_segment));
return { segment, offset };
}
template<typename CPU>
inline LogicalAddress MemoryOrRegisterReference::resolve32(const CPU& cpu, Optional<SegmentRegister> segment_prefix)
{
ASSERT(m_a32);
auto default_segment = SegmentRegister::DS;
u32 offset = 0;
switch (m_rm & 0x07) {
case 0:
offset = cpu.eax() + m_displacement32;
break;
case 1:
offset = cpu.ecx() + m_displacement32;
break;
case 2:
offset = cpu.edx() + m_displacement32;
break;
case 3:
offset = cpu.ebx() + m_displacement32;
break;
case 4:
offset = evaluate_sib(cpu, default_segment);
break;
case 6:
offset = cpu.esi() + m_displacement32;
break;
case 7:
offset = cpu.edi() + m_displacement32;
break;
default: // 5
if ((m_rm & 0xc0) == 0x00) {
offset = m_displacement32;
break;
} else {
default_segment = SegmentRegister::SS;
offset = cpu.ebp() + m_displacement32;
break;
}
break;
}
u16 segment = cpu.segment(segment_prefix.value_or(default_segment));
return { segment, offset };
}
template<typename CPU>
inline u32 MemoryOrRegisterReference::evaluate_sib(const CPU& cpu, SegmentRegister& default_segment) const
{
u32 scale = 0;
switch (m_sib & 0xc0) {
case 0x00:
scale = 1;
break;
case 0x40:
scale = 2;
break;
case 0x80:
scale = 4;
break;
case 0xc0:
scale = 8;
break;
}
u32 index = 0;
switch ((m_sib >> 3) & 0x07) {
case 0:
index = cpu.eax();
break;
case 1:
index = cpu.ecx();
break;
case 2:
index = cpu.edx();
break;
case 3:
index = cpu.ebx();
break;
case 4:
index = 0;
break;
case 5:
index = cpu.ebp();
break;
case 6:
index = cpu.esi();
break;
case 7:
index = cpu.edi();
break;
}
u32 base = m_displacement32;
switch (m_sib & 0x07) {
case 0:
base += cpu.eax();
break;
case 1:
base += cpu.ecx();
break;
case 2:
base += cpu.edx();
break;
case 3:
base += cpu.ebx();
break;
case 4:
default_segment = SegmentRegister::SS;
base += cpu.esp();
break;
case 6:
base += cpu.esi();
break;
case 7:
base += cpu.edi();
break;
default: // 5
switch ((m_rm >> 6) & 3) {
case 0:
break;
case 1:
case 2:
default_segment = SegmentRegister::SS;
base += cpu.ebp();
break;
default:
ASSERT_NOT_REACHED();
break;
}
break;
}
return (scale * index) + base;
}
template<typename CPU>
inline void MemoryOrRegisterReference::write32(CPU& cpu, const Instruction& insn, u32 value)
{
if (is_register()) {
cpu.gpr32(reg32()) = value;
return;
}
auto address = resolve32(cpu, insn.segment_prefix());
cpu.write_memory32(address, value);
}
template<typename CPU>
inline u32 MemoryOrRegisterReference::read32(CPU& cpu, const Instruction& insn)
{
if (is_register())
return cpu.gpr32(reg32());
auto address = resolve32(cpu, insn.segment_prefix());
return cpu.read_memory32(address);
}
}