Mu - subx/021byte_addressing.cc

From 6e1eeeebfb453fa7c871869c19375ce60fbd7413 Mon Sep 17 00:00:00 2001 From: Kartik Agaram Date: Sat, 27 Jul 2019 16:01:55 -0700 Subject: 5485 - promote SubX to top-level --- html/021byte_addressing.cc.html | 239 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 239 insertions(+) create mode 100644 html/021byte_addressing.cc.html (limited to 'html/021byte_addressing.cc.html') diff --git a/html/021byte_addressing.cc.html b/html/021byte_addressing.cc.html new file mode 100644 index 00000000..32a3d7bb --- /dev/null +++ b/html/021byte_addressing.cc.html @@ -0,0 +1,239 @@ + + + + +Mu - subx/021byte_addressing.cc + + + + + + + + + + +https://github.com/akkartik/mu/blob/master/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(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       "== code 0x1\n"
+ 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       "== data 0x2000\n"
+ 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       "== code 0x1\n"
+ 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       "== data 0x2000\n"
+ 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       "== code 0x1\n"
+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       "== code 0x1\n"
+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       "== data 0x2000\n"
+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 << NUM(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 }
+
+ + + -- cgit 1.4.1-2-gfad0