diff options
Diffstat (limited to 'subx/021byte_addressing.cc')
| -rw-r--r-- | subx/021byte_addressing.cc | 83 |
1 files changed, 68 insertions, 15 deletions
diff --git a/subx/021byte_addressing.cc b/subx/021byte_addressing.cc index 84a51779..b49718d1 100644 --- a/subx/021byte_addressing.cc +++ b/subx/021byte_addressing.cc @@ -1,18 +1,55 @@ -//: +//: SubX mostly deals with instructions operating on 32-bit operands, but we +//: still need to deal with raw bytes for strings and so on. + +//: Unfortunately the register encodings when dealing with bytes are a mess. +//: We need a special case for them. +:(code) +string rname_8bit(uint8_t r) { + switch (r) { + case 0: return "AL"; // lowest byte of EAX + case 1: return "CL"; // lowest byte of ECX + case 2: return "DL"; // lowest byte of EDX + case 3: return "BL"; // lowest byte of EBX + case 4: return "AH"; // second lowest byte of EAX + case 5: return "CH"; // second lowest byte of ECX + case 6: return "DH"; // second lowest byte of EDX + case 7: return "BH"; // second lowest byte of EBX + default: raise << "invalid 8-bit register " << r << '\n' << end(); return ""; + } +} + +uint8_t* effective_byte_address(uint8_t modrm) { + uint8_t mod = (modrm>>6); + uint8_t rm = modrm & 0x7; + if (mod == 3) { + // select an 8-bit register + trace(90, "run") << "r/m8 is " << rname_8bit(rm) << end(); + return reg_8bit(rm); + } + // the rest is as usual + return mem_addr_u8(effective_address_number(modrm)); +} + +uint8_t* reg_8bit(uint8_t rm) { + uint8_t* result = reinterpret_cast<uint8_t*>(&Reg[rm & 0x3].i); // _L register + if (rm & 0x4) + ++result; // _H register; assumes host is little-endian + return result; +} :(before "End Initialize Op Names(name)") -put(name, "88", "copy r8 (lowermost byte of r32) to r8/m8-at-r32"); +put(name, "88", "copy r8 to r8/m8-at-r32"); :(scenario copy_r8_to_mem_at_r32) % Reg[EBX].i = 0x224488ab; % Reg[EAX].i = 0x2000; == 0x1 # op ModR/M SIB displacement immediate - 88 18 # copy just the lowermost byte of EBX to the byte at *EAX -# ModR/M in binary: 00 (indirect mode) 011 (src EBX) 000 (dest EAX) + 88 18 # copy BL to the byte at *EAX +# ModR/M in binary: 00 (indirect mode) 011 (src BL) 000 (dest EAX) == 0x2000 f0 cc bb aa # 0xf0 with more data in following bytes -+run: copy lowermost byte of EBX to r8/m8-at-r32 ++run: copy BL to r8/m8-at-r32 +run: effective address is 0x2000 (EAX) +run: storing 0xab % CHECK_EQ(0xaabbccab, read_mem_u32(0x2000)); @@ -21,10 +58,11 @@ f0 cc bb aa # 0xf0 with more data in following bytes case 0x88: { // copy r8 to r/m8 const uint8_t modrm = next(); const uint8_t rsrc = (modrm>>3)&0x7; - trace(90, "run") << "copy lowermost byte of " << rname(rsrc) << " to r8/m8-at-r32" << end(); + trace(90, "run") << "copy " << rname_8bit(rsrc) << " to r8/m8-at-r32" << end(); // use unsigned to zero-extend 8-bit value to 32 bits - uint8_t* dest = reinterpret_cast<uint8_t*>(effective_address(modrm)); - *dest = Reg[rsrc].u; + uint8_t* dest = reinterpret_cast<uint8_t*>(effective_byte_address(modrm)); + const uint8_t* src = reg_8bit(rsrc); + *dest = *src; trace(90, "run") << "storing 0x" << HEXBYTE << NUM(*dest) << end(); break; } @@ -32,18 +70,18 @@ case 0x88: { // copy r8 to r/m8 //: :(before "End Initialize Op Names(name)") -put(name, "8a", "copy r8/m8-at-r32 to r8 (lowermost byte of r32)"); +put(name, "8a", "copy r8/m8-at-r32 to r8"); :(scenario copy_mem_at_r32_to_r8) % Reg[EBX].i = 0xaabbcc0f; // one nibble each of lowest byte set to all 0s and all 1s, to maximize value of this test % Reg[EAX].i = 0x2000; == 0x1 # op ModR/M SIB displacement immediate - 8a 18 # copy just the byte at *EAX to lowermost byte of EBX (clearing remaining bytes) + 8a 18 # copy just the byte at *EAX to BL # ModR/M in binary: 00 (indirect mode) 011 (dest EBX) 000 (src EAX) == 0x2000 # data segment ab ff ff ff # 0xab with more data in following bytes -+run: copy r8/m8-at-r32 to lowermost byte of EBX ++run: copy r8/m8-at-r32 to BL +run: effective address is 0x2000 (EAX) +run: storing 0xab # remaining bytes of EBX are *not* cleared @@ -53,11 +91,26 @@ ab ff ff ff # 0xab with more data in following bytes case 0x8a: { // copy r/m8 to r8 const uint8_t modrm = next(); const uint8_t rdest = (modrm>>3)&0x7; - trace(90, "run") << "copy r8/m8-at-r32 to lowermost byte of " << rname(rdest) << end(); + trace(90, "run") << "copy r8/m8-at-r32 to " << rname_8bit(rdest) << end(); // use unsigned to zero-extend 8-bit value to 32 bits - const uint8_t* src = reinterpret_cast<uint8_t*>(effective_address(modrm)); + const uint8_t* src = reinterpret_cast<uint8_t*>(effective_byte_address(modrm)); + uint8_t* dest = reg_8bit(rdest); trace(90, "run") << "storing 0x" << HEXBYTE << NUM(*src) << end(); - *reinterpret_cast<uint8_t*>(&Reg[rdest].u) = *src; // assumes host is little-endian - trace(90, "run") << rname(rdest) << " now contains 0x" << HEXWORD << Reg[rdest].u << end(); + *dest = *src; + const uint8_t rdest_32bit = rdest & 0x3; + trace(90, "run") << rname(rdest_32bit) << " now contains 0x" << HEXWORD << Reg[rdest_32bit].u << end(); break; } + +:(scenario cannot_copy_byte_to_ESP_EBP_ESI_EDI) +% Reg[ESI].u = 0xaabbccdd; +% Reg[EBX].u = 0x11223344; +== 0x1 +# op ModR/M SIB displacement immediate + 8a f3 # copy just the byte at *EBX to 8-bit register '6' +# ModR/M in binary: 11 (direct mode) 110 (dest 8-bit 'register 6') 011 (src EBX) +# ensure 8-bit register '6' is DH, not ESI ++run: copy r8/m8-at-r32 to DH ++run: storing 0x44 +# ensure ESI is unchanged +% CHECK_EQ(Reg[ESI].u, 0xaabbccdd); |