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Diffstat (limited to 'subx/016index_addressing.cc')
-rw-r--r-- | subx/016index_addressing.cc | 125 |
1 files changed, 125 insertions, 0 deletions
diff --git a/subx/016index_addressing.cc b/subx/016index_addressing.cc new file mode 100644 index 00000000..b1b7e563 --- /dev/null +++ b/subx/016index_addressing.cc @@ -0,0 +1,125 @@ +//: operating on memory at the address provided by some register plus optional scale and offset + +:(scenario add_r32_to_mem_at_r32_with_sib) +% Reg[EBX].i = 0x10; +% Reg[EAX].i = 0x60; +== 0x1 # code segment +# op ModR/M SIB displacement immediate + 01 1c 20 # add EBX to *EAX +# ModR/M in binary: 00 (indirect mode) 011 (src EBX) 100 (dest in SIB) +# SIB in binary: 00 (scale 1) 100 (no index) 000 (base EAX) +== 0x60 # data segment +01 00 00 00 # 1 ++run: add EBX to r/m32 ++run: effective address is initially 0x60 (EAX) ++run: effective address is 0x60 ++run: storing 0x00000011 + +:(before "End Mod 0 Special-cases(addr)") +case 4: // exception: mod 0b00 rm 0b100 => incoming SIB (scale-index-base) byte + addr = effective_address_from_sib(mod); + break; +:(code) +uint32_t effective_address_from_sib(uint8_t mod) { + uint8_t sib = next(); + uint8_t base = sib&0x7; + uint32_t addr = 0; + if (base != EBP || mod != 0) { + addr = Reg[base].u; + trace(90, "run") << "effective address is initially 0x" << std::hex << addr << " (" << rname(base) << ")" << end(); + } + else { + // base == EBP && mod == 0 + addr = imm32(); // ignore base + trace(90, "run") << "effective address is initially 0x" << std::hex << addr << " (disp32)" << end(); + } + uint8_t index = (sib>>3)&0x7; + if (index == ESP) { + // ignore index and scale + trace(90, "run") << "effective address is 0x" << std::hex << addr << end(); + } + else { + uint8_t scale = (1 << (sib>>6)); + addr += Reg[index].i*scale; // treat index register as signed. Maybe base as well? But we'll always ensure it's non-negative. + trace(90, "run") << "effective address is 0x" << std::hex << addr << " (after adding " << rname(index) << "*" << NUM(scale) << ")" << end(); + } + return addr; +} + +:(scenario add_r32_to_mem_at_base_r32_index_r32) +% Reg[EBX].i = 0x10; // source +% Reg[EAX].i = 0x5e; // dest base +% Reg[ECX].i = 0x2; // dest index +== 0x1 # code segment +# op ModR/M SIB displacement immediate + 01 1c 08 # add EBX to *(EAX+ECX) +# ModR/M in binary: 00 (indirect mode) 011 (src EBX) 100 (dest in SIB) +# SIB in binary: 00 (scale 1) 001 (index ECX) 000 (base EAX) +== 0x60 # data segment +01 00 00 00 # 1 ++run: add EBX to r/m32 ++run: effective address is initially 0x5e (EAX) ++run: effective address is 0x60 (after adding ECX*1) ++run: storing 0x00000011 + +:(scenario add_r32_to_mem_at_displacement_using_sib) +% Reg[EBX].i = 0x10; // source +== 0x1 # code segment +# op ModR/M SIB displacement immediate + 01 1c 25 60 00 00 00 # add EBX to *0x60 +# ModR/M in binary: 00 (indirect mode) 011 (src EBX) 100 (dest in SIB) +# SIB in binary: 00 (scale 1) 100 (no index) 101 (not EBP but disp32) +== 0x60 # data segment +01 00 00 00 # 1 ++run: add EBX to r/m32 ++run: effective address is initially 0x60 (disp32) ++run: effective address is 0x60 ++run: storing 0x00000011 + +//: + +:(scenario add_r32_to_mem_at_base_r32_index_r32_plus_disp8) +% Reg[EBX].i = 0x10; // source +% Reg[EAX].i = 0x59; // dest base +% Reg[ECX].i = 0x5; // dest index +== 0x1 # code segment +# op ModR/M SIB displacement immediate + 01 5c 08 02 # add EBX to *(EAX+ECX+2) +# ModR/M in binary: 01 (indirect+disp8 mode) 011 (src EBX) 100 (dest in SIB) +# SIB in binary: 00 (scale 1) 001 (index ECX) 000 (base EAX) +== 0x60 # data segment +01 00 00 00 # 1 ++run: add EBX to r/m32 ++run: effective address is initially 0x59 (EAX) ++run: effective address is 0x5e (after adding ECX*1) ++run: effective address is 0x60 (after adding disp8) ++run: storing 0x00000011 + +:(before "End Mod 1 Special-cases(addr)") +case 4: // exception: mod 0b01 rm 0b100 => incoming SIB (scale-index-base) byte + addr = effective_address_from_sib(mod); + break; + +//: + +:(scenario add_r32_to_mem_at_base_r32_index_r32_plus_disp32) +% Reg[EBX].i = 0x10; // source +% Reg[EAX].i = 0x59; // dest base +% Reg[ECX].i = 0x5; // dest index +== 0x1 # code segment +# op ModR/M SIB displacement immediate + 01 9c 08 02 00 00 00 # add EBX to *(EAX+ECX+2) +# ModR/M in binary: 10 (indirect+disp32 mode) 011 (src EBX) 100 (dest in SIB) +# SIB in binary: 00 (scale 1) 001 (index ECX) 000 (base EAX) +== 0x60 # data segment +01 00 00 00 # 1 ++run: add EBX to r/m32 ++run: effective address is initially 0x59 (EAX) ++run: effective address is 0x5e (after adding ECX*1) ++run: effective address is 0x60 (after adding disp32) ++run: storing 0x00000011 + +:(before "End Mod 2 Special-cases(addr)") +case 4: // exception: mod 0b10 rm 0b100 => incoming SIB (scale-index-base) byte + addr = effective_address_from_sib(mod); + break; |