diff options
author | Kartik K. Agaram <vc@akkartik.com> | 2017-10-12 23:07:11 -0700 |
---|---|---|
committer | Kartik K. Agaram <vc@akkartik.com> | 2017-10-12 23:17:46 -0700 |
commit | 159af423673c96a35947e85a788689d216f6e2fb (patch) | |
tree | af21c8738d0d3c5ba4b9dce50b67b61641096644 /subx/011indirect_addressing.cc | |
parent | 293dd258ff27405b451bc728366695f20e7286a8 (diff) | |
download | mu-159af423673c96a35947e85a788689d216f6e2fb.tar.gz |
4049
Instead of organizing layers by instruction, do so by addressing mode.
Diffstat (limited to 'subx/011indirect_addressing.cc')
-rw-r--r-- | subx/011indirect_addressing.cc | 117 |
1 files changed, 117 insertions, 0 deletions
diff --git a/subx/011indirect_addressing.cc b/subx/011indirect_addressing.cc new file mode 100644 index 00000000..8800727e --- /dev/null +++ b/subx/011indirect_addressing.cc @@ -0,0 +1,117 @@ +//: operating on memory at the address provided by some register + +:(scenario add_r32_to_mem_at_r32) +% Reg[3].i = 0x10; +% Reg[0].i = 0x60; +# word in addresses 0x60-0x63 has value 1 +% Mem.at(0x60) = 1; +# op ModR/M SIB displacement immediate + 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 0x00000011 + +:(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 reg " << NUM(arg2) << " to effective address" << end(); + int32_t* arg1 = effective_address(modrm); + BINARY_ARITHMETIC_OP(+, *arg1, Reg[arg2].i); + break; +} + +:(code) +// Implement tables 2-2 and 2-3 in the Intel manual, Volume 2. +// We return a pointer so that instructions can write to multiple bytes in +// 'Mem' at once. +int32_t* effective_address(uint8_t modrm) { + uint8_t mod = (modrm>>6); + // ignore middle 3 'reg opcode' bits + uint8_t rm = modrm & 0x7; + int32_t* result = 0; + switch (mod) { + case 0: + // mod 0 is usually indirect addressing + switch (rm) { + default: + trace(2, "run") << "effective address is mem at address 0x" << std::hex << Reg[rm].u << " (reg " << NUM(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; + // End Mod 0 Special-cases + } + break; + // End Mod Special-cases + default: + cerr << "unrecognized mod bits: " << NUM(mod) << '\n'; + exit(1); + } + return result; +} + +//: + +:(scenario add_mem_at_r32_to_r32) +% Reg[0].i = 0x60; +% Reg[3].i = 0x10; +% Mem.at(0x60) = 1; +# op ModR/M SIB displacement immediate + 03 18 # add *EAX (reg 0) to EBX (reg 3) ++run: add effective address to reg 3 ++run: effective address is mem at address 0x60 (reg 0) ++run: storing 0x00000011 + +:(before "End Single-Byte Opcodes") +case 0x03: { // add r/m32 to r32 + uint8_t modrm = next(); + uint8_t arg1 = (modrm>>3)&0x7; + trace(2, "run") << "add effective address to reg " << NUM(arg1) << end(); + const int32_t* arg2 = effective_address(modrm); + BINARY_ARITHMETIC_OP(+, Reg[arg1].i, *arg2); + break; +} + +//:: subtract + +:(scenario sub_r32_from_mem_at_r32) +% Reg[0].i = 0x60; +% Mem.at(0x60) = 10; +% Reg[3].i = 1; +# op ModRM SIB displacement immediate + 29 18 # subtract EBX (reg 3) from *EAX (reg 0) ++run: subtract reg 3 from effective address ++run: effective address is mem at address 0x60 (reg 0) ++run: storing 0x00000009 + +:(before "End Single-Byte Opcodes") +case 0x29: { // subtract r32 from r/m32 + uint8_t modrm = next(); + uint8_t arg2 = (modrm>>3)&0x7; + trace(2, "run") << "subtract reg " << NUM(arg2) << " from effective address" << end(); + int32_t* arg1 = effective_address(modrm); + BINARY_ARITHMETIC_OP(-, *arg1, Reg[arg2].i); + break; +} + +//: + +:(scenario sub_mem_at_r32_from_r32) +% Reg[0].i = 0x60; +% Mem.at(0x60) = 1; +% Reg[3].i = 10; +# op ModRM SIB displacement immediate + 2b 18 # subtract *EAX (reg 0) from EBX (reg 3) ++run: subtract effective address from reg 3 ++run: effective address is mem at address 0x60 (reg 0) ++run: storing 0x00000009 + +:(before "End Single-Byte Opcodes") +case 0x2b: { // subtract r/m32 from r32 + uint8_t modrm = next(); + uint8_t arg1 = (modrm>>3)&0x7; + trace(2, "run") << "subtract effective address from reg " << NUM(arg1) << end(); + const int32_t* arg2 = effective_address(modrm); + BINARY_ARITHMETIC_OP(-, Reg[arg1].i, *arg2); + break; +} |