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This commit is contained in:
Kartik K. Agaram 2017-10-12 17:57:59 -07:00
parent bcafd01fdf
commit 7c0f7d69ae
1 changed files with 6 additions and 6 deletions
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12
subx/011add.cc
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@ -4,16 +4,16 @@
# word in addresses 0x60-0x63 has value 1
% Mem[0x60] = 1;
# op ModR/M SIB displacement immediate
01 18 # add EBX to *EAX
+run: add register 3 to effective address
+run: effective address is memory at address 0x60 (register 0)
01 18 # add EBX (reg 3) to *EAX (reg 0)
+run: add reg 3 to effective address
+run: effective address is mem at address 0x60 (reg 0)
+run: storing 0x11
:(before "End Single-Byte Opcodes")
case 0x01: { // add r32 to r/m32
uint8_t modrm = next();
uint8_t arg2 = (modrm>>3)&0x7;
trace(2, "run") << "add register " << static_cast<int>(arg2) << " to effective address" << end();
trace(2, "run") << "add reg " << static_cast<int>(arg2) << " to effective address" << end();
int32_t* arg1 = effective_address(modrm);
BINARY_ARITHMETIC_OP(+, *arg1, Reg[arg2].i);
break;
@ -25,7 +25,7 @@ case 0x01: { // add r32 to r/m32
// 'Mem' at once.
int32_t* effective_address(uint8_t modrm) {
uint8_t mod = (modrm>>6);
// ignore middle 3 'register opcode' bits
// ignore middle 3 'reg opcode' bits
uint8_t rm = modrm & 0x7;
int32_t* result = 0;
switch (mod) {
@ -33,7 +33,7 @@ int32_t* effective_address(uint8_t modrm) {
// mod 0 is usually indirect addressing
switch (rm) {
default:
trace(99, "run") << "effective address is memory at address 0x" << std::hex << Reg[rm].u << " (register " << static_cast<int>(rm) << ")" << end();
trace(99, "run") << "effective address is mem at address 0x" << std::hex << Reg[rm].u << " (reg " << static_cast<int>(rm) << ")" << end();
assert(Reg[rm].u + sizeof(int32_t) <= Mem.size());
result = reinterpret_cast<int32_t*>(&Mem.at(Reg[rm].u)); // rely on the host itself being in little-endian order
break;