Mu - subx/021byte_addressing.cc

From 104e521c04d1a0cad9c68fb11e250e12ad8917ef Mon Sep 17 00:00:00 2001 From: Kartik Agaram Date: Wed, 17 Oct 2018 07:08:47 -0700 Subject: 4709 --- html/subx/021byte_addressing.cc.html | 181 +++++++++++++++++++++++++++++++++++ 1 file changed, 181 insertions(+) create mode 100644 html/subx/021byte_addressing.cc.html (limited to 'html/subx/021byte_addressing.cc.html') diff --git a/html/subx/021byte_addressing.cc.html b/html/subx/021byte_addressing.cc.html new file mode 100644 index 00000000..8c0e583a --- /dev/null +++ b/html/subx/021byte_addressing.cc.html @@ -0,0 +1,181 @@ + + + + +Mu - subx/021byte_addressing.cc + + + + + + + + + + +

+  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(90, "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 :(scenario copy_r8_to_mem_at_r32)
+ 44 % Reg[EBX].i = 0x224488ab;
+ 45 % Reg[EAX].i = 0x2000;
+ 46 == 0x1
+ 47 # op  ModR/M  SIB   displacement  immediate
+ 48   88  18                                      # copy BL to the byte at *EAX
+ 49 # ModR/M in binary: 00 (indirect mode) 011 (src BL) 000 (dest EAX)
+ 50 == 0x2000
+ 51 f0 cc bb aa  # 0xf0 with more data in following bytes
+ 52 +run: copy BL to r8/m8-at-r32
+ 53 +run: effective address is 0x2000 (EAX)
+ 54 +run: storing 0xab
+ 55 % CHECK_EQ(0xaabbccab, read_mem_u32(0x2000));
+ 56 
+ 57 :(before "End Single-Byte Opcodes")
+ 58 case 0x88: {  // copy r8 to r/m8
+ 59   const uint8_t modrm = next();
+ 60   const uint8_t rsrc = (modrm>>3)&0x7;
+ 61   trace(90, "run") << "copy " << rname_8bit(rsrc) << " to r8/m8-at-r32" << end();
+ 62   // use unsigned to zero-extend 8-bit value to 32 bits
+ 63   uint8_t* dest = reinterpret_cast<uint8_t*>(effective_byte_address(modrm));
+ 64   const uint8_t* src = reg_8bit(rsrc);
+ 65   *dest = *src;
+ 66   trace(90, "run") << "storing 0x" << HEXBYTE << NUM(*dest) << end();
+ 67   break;
+ 68 }
+ 69 
+ 70 //:
+ 71 
+ 72 :(before "End Initialize Op Names")
+ 73 put_new(Name, "8a", "copy r8/m8-at-r32 to r8");
+ 74 
+ 75 :(scenario copy_mem_at_r32_to_r8)
+ 76 % Reg[EBX].i = 0xaabbcc0f;  // one nibble each of lowest byte set to all 0s and all 1s, to maximize value of this test
+ 77 % Reg[EAX].i = 0x2000;
+ 78 == 0x1
+ 79 # op  ModR/M  SIB   displacement  immediate
+ 80   8a  18                                      # copy just the byte at *EAX to BL
+ 81 # ModR/M in binary: 00 (indirect mode) 011 (dest EBX) 000 (src EAX)
+ 82 == 0x2000  # data segment
+ 83 ab ff ff ff  # 0xab with more data in following bytes
+ 84 +run: copy r8/m8-at-r32 to BL
+ 85 +run: effective address is 0x2000 (EAX)
+ 86 +run: storing 0xab
+ 87 # remaining bytes of EBX are *not* cleared
+ 88 +run: EBX now contains 0xaabbccab
+ 89 
+ 90 :(before "End Single-Byte Opcodes")
+ 91 case 0x8a: {  // copy r/m8 to r8
+ 92   const uint8_t modrm = next();
+ 93   const uint8_t rdest = (modrm>>3)&0x7;
+ 94   trace(90, "run") << "copy r8/m8-at-r32 to " << rname_8bit(rdest) << end();
+ 95   // use unsigned to zero-extend 8-bit value to 32 bits
+ 96   const uint8_t* src = reinterpret_cast<uint8_t*>(effective_byte_address(modrm));
+ 97   uint8_t* dest = reg_8bit(rdest);
+ 98   trace(90, "run") << "storing 0x" << HEXBYTE << NUM(*src) << end();
+ 99   *dest = *src;
+100   const uint8_t rdest_32bit = rdest & 0x3;
+101   trace(90, "run") << rname(rdest_32bit) << " now contains 0x" << HEXWORD << Reg[rdest_32bit].u << end();
+102   break;
+103 }
+104 
+105 :(scenario cannot_copy_byte_to_ESP_EBP_ESI_EDI)
+106 % Reg[ESI].u = 0xaabbccdd;
+107 % Reg[EBX].u = 0x11223344;
+108 == 0x1
+109 # op  ModR/M  SIB   displacement  immediate
+110   8a  f3                                      # copy just the byte at *EBX to 8-bit register '6'
+111 # ModR/M in binary: 11 (direct mode) 110 (dest 8-bit 'register 6') 011 (src EBX)
+112 # ensure 8-bit register '6' is DH, not ESI
+113 +run: copy r8/m8-at-r32 to DH
+114 +run: storing 0x44
+115 # ensure ESI is unchanged
+116 % CHECK_EQ(Reg[ESI].u, 0xaabbccdd);
+

+ + + -- cgit 1.4.1-2-gfad0