1 //: SubX mostly deals with instructions operating on 32-bit operands, but we
  2 //: still need to deal with raw bytes for strings and so on.
  3 
  4 //: Unfortunately the register encodings when dealing with bytes are a mess.
  5 //: We need a special case for them.
  6 :(code)
  7 string rname_8bit(uint8_t r) {
  8   switch (r) {
  9   case 0: return "AL";  // lowest byte of EAX
 10   case 1: return "CL";  // lowest byte of ECX
 11   case 2: return "DL";  // lowest byte of EDX
 12   case 3: return "BL";  // lowest byte of EBX
 13   case 4: return "AH";  // second lowest byte of EAX
 14   case 5: return "CH";  // second lowest byte of ECX
 15   case 6: return "DH";  // second lowest byte of EDX
 16   case 7: return "BH";  // second lowest byte of EBX
 17   default: raise << "invalid 8-bit register " << r << '\n' << end();  return "";
 18   }
 19 }
 20 
 21 uint8_t* effective_byte_address(uint8_t modrm) {
 22   uint8_t mod = (modrm>>6);
 23   uint8_t rm = modrm & 0x7;
 24   if (mod == 3) {
 25     // select an 8-bit register
 26     trace(Callstack_depth+1, "run") << "r/m8 is " << rname_8bit(rm) << end();
 27     return reg_8bit(rm);
 28   }
 29   // the rest is as usual
 30   return mem_addr_u8(effective_address_number(modrm));
 31 }
 32 
 33 uint8_t* reg_8bit(uint8_t rm) {
 34   uint8_t* result = reinterpret_cast<uint8_t*>(&Reg[rm & 0x3].i);  // _L register
 35   if (rm & 0x4)
 36     ++result;  // _H register;  assumes host is little-endian
 37   return result;
 38 }
 39 
 40 :(before "End Initialize Op Names")
 41 put_new(Name, "88", "copy r8 to r8/m8-at-r32");
 42 
 43 :(code)
 44 void test_copy_r8_to_mem_at_r32() {
 45   Reg[EBX].i = 0x224488ab;
 46   Reg[EAX].i = 0x2000;
 47   run(
 48       "== 0x1\n"  // code segment
 49       // op     ModR/M  SIB   displacement  immediate
 50       "  88     18                                      \n"  // copy BL to the byte at *EAX
 51       // ModR/M in binary: 00 (indirect mode) 011 (src BL) 000 (dest EAX)
 52       "== 0x2000\n"  // data segment
 53       "f0 cc bb aa\n"
 54   );
 55   CHECK_TRACE_CONTENTS(
 56       "run: copy BL to r8/m8-at-r32\n"
 57       "run: effective address is 0x00002000 (EAX)\n"
 58       "run: storing 0xab\n"
 59   );
 60   CHECK_EQ(0xaabbccab, read_mem_u32(0x2000));
 61 }
 62 
 63 :(before "End Single-Byte Opcodes")
 64 case 0x88: {  // copy r8 to r/m8
 65   const uint8_t modrm = next();
 66   const uint8_t rsrc = (modrm>>3)&0x7;
 67   trace(Callstack_depth+1, "run") << "copy " << rname_8bit(rsrc) << " to r8/m8-at-r32" << end();
 68   // use unsigned to zero-extend 8-bit value to 32 bits
 69   uint8_t* dest = reinterpret_cast<uint8_t*>(effective_byte_address(modrm));
 70   const uint8_t* src = reg_8bit(rsrc);
 71   *dest = *src;
 72   trace(Callstack_depth+1, "run") << "storing 0x" << HEXBYTE << NUM(*dest) << end();
 73   break;
 74 }
 75 
 76 //:
 77 
 78 :(before "End Initialize Op Names")
 79 put_new(Name, "8a", "copy r8/m8-at-r32 to r8");
 80 
 81 :(code)
 82 void test_copy_mem_at_r32_to_r8() {
 83   Reg[EBX].i = 0xaabbcc0f;  // one nibble each of lowest byte set to all 0s and all 1s, to maximize value of this test
 84   Reg[EAX].i = 0x2000;
 85   run(
 86       "== 0x1\n"  // code segment
 87       // op     ModR/M  SIB   displacement  immediate
 88       "  8a     18                                      \n"  // copy just the byte at *EAX to BL
 89       // ModR/M in binary: 00 (indirect mode) 011 (dest EBX) 000 (src EAX)
 90       "== 0x2000\n"  // data segment
 91       "ab ff ff ff\n"  // 0xab with more data in following bytes
 92   );
 93   CHECK_TRACE_CONTENTS(
 94       "run: copy r8/m8-at-r32 to BL\n"
 95       "run: effective address is 0x00002000 (EAX)\n"
 96       "run: storing 0xab\n"
 97       // remaining bytes of EBX are *not* cleared
 98       "run: EBX now contains 0xaabbccab\n"
 99   );
100 }
101 
102 :(before "End Single-Byte Opcodes")
103 case 0x8a: {  // copy r/m8 to r8
104   const uint8_t modrm = next();
105   const uint8_t rdest = (modrm>>3)&0x7;
106   trace(Callstack_depth+1, "run") << "copy r8/m8-at-r32 to " << rname_8bit(rdest) << end();
107   // use unsigned to zero-extend 8-bit value to 32 bits
108   const uint8_t* src = reinterpret_cast<uint8_t*>(effective_byte_address(modrm));
109   uint8_t* dest = reg_8bit(rdest);
110   trace(Callstack_depth+1, "run") << "storing 0x" << HEXBYTE << NUM(*src) << end();
111   *dest = *src;
112   const uint8_t rdest_32bit = rdest & 0x3;
113   trace(Callstack_depth+1, "run") << rname(rdest_32bit) << " now contains 0x" << HEXWORD << Reg[rdest_32bit].u << end();
114   break;
115 }
116 
117 :(code)
118 void test_cannot_copy_byte_to_ESP_EBP_ESI_EDI() {
119   Reg[ESI].u = 0xaabbccdd;
120   Reg[EBX].u = 0x11223344;
121   run(
122       "== 0x1\n"  // code segment
123       // op     ModR/M  SIB   displacement  immediate
124       "  8a     f3                                      \n"  // copy just the byte at *EBX to 8-bit register '6'
125       // ModR/M in binary: 11 (direct mode) 110 (dest 8-bit 'register 6') 011 (src EBX)
126   );
127   CHECK_TRACE_CONTENTS(
128       // ensure 8-bit register '6' is DH, not ESI
129       "run: copy r8/m8-at-r32 to DH\n"
130       "run: storing 0x44\n"
131   );
132   // ensure ESI is unchanged
133   CHECK_EQ(Reg[ESI].u, 0xaabbccdd);
134 }
135 
136 //:
137 
138 :(before "End Initialize Op Names")
139 put_new(Name, "c6", "copy imm8 to r8/m8-at-r32 (mov)");
140 
141 :(code)
142 void test_copy_imm8_to_mem_at_r32() {
143   Reg[EAX].i = 0x2000;
144   run(
145       "== 0x1\n"  // code segment
146       // op     ModR/M  SIB   displacement  immediate
147       "  c6     00                          dd          \n"  // copy to the byte at *EAX
148       // ModR/M in binary: 00 (indirect mode) 000 (unused) 000 (dest EAX)
149       "== 0x2000\n"  // data segment
150       "f0 cc bb aa\n"
151   );
152   CHECK_TRACE_CONTENTS(
153       "run: copy imm8 to r8/m8-at-r32\n"
154       "run: effective address is 0x00002000 (EAX)\n"
155       "run: storing 0xdd\n"
156   );
157   CHECK_EQ(0xaabbccdd, read_mem_u32(0x2000));
158 }
159 
160 :(before "End Single-Byte Opcodes")
161 case 0xc6: {  // copy imm8 to r/m8
162   const uint8_t modrm = next();
163   const uint8_t src = next();
164   trace(Callstack_depth+1, "run") << "copy imm8 to r8/m8-at-r32" << end();
165   trace(Callstack_depth+1, "run") << "imm8 is 0x" << HEXWORD << src << end();
166   const uint8_t subop = (modrm>>3)&0x7;  // middle 3 'reg opcode' bits
167   if (subop != 0) {
168     cerr << "unrecognized subop for opcode c6: " << NUM(subop) << " (only 0/copy currently implemented)\n";
169     exit(1);
170   }
171   // use unsigned to zero-extend 8-bit value to 32 bits
172   uint8_t* dest = reinterpret_cast<uint8_t*>(effective_byte_address(modrm));
173   *dest = src;
174   trace(Callstack_depth+1, "run") << "storing 0x" << HEXBYTE << NUM(*dest) << end();
175   break;
176 }