75 lines
2.8 KiB
C++
75 lines
2.8 KiB
C++
//: operating on memory at the address provided by some register plus optional scale and offset
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:(scenario add_r32_to_mem_at_r32_with_sib)
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% Reg[3].i = 0x10;
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% Reg[0].i = 0x60;
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% SET_WORD_IN_MEM(0x60, 1);
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# op ModR/M SIB displacement immediate
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01 1c 20 # add EBX to *EAX
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# ModR/M in binary: 00 (indirect mode) 011 (src EBX) 100 (dest in SIB)
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# SIB in binary: 00 (scale 1) 100 (no index) 000 (base EAX)
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+run: add EBX to r/m32
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+run: effective address is initially 0x60 (EAX)
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+run: effective address is 0x60
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+run: storing 0x00000011
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:(before "End Mod 0 Special-cases")
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case 4: { // exception: mod 0b00 rm 0b100 => incoming SIB (scale-index-base) byte
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uint32_t addr = effective_address_from_sib(mod);
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if (addr == 0) break;
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result = reinterpret_cast<int32_t*>(&Mem.at(addr));
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break;
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}
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:(code)
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uint32_t effective_address_from_sib(uint8_t mod) {
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uint8_t sib = next();
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uint8_t base = sib&0x7;
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uint32_t addr = 0;
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if (base != EBP || mod != 0) {
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addr = Reg[base].u;
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trace(2, "run") << "effective address is initially 0x" << std::hex << addr << " (" << rname(base) << ")" << end();
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}
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else {
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// base == EBP && mod == 0
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addr = imm32(); // ignore base
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trace(2, "run") << "effective address is initially 0x" << std::hex << addr << " (disp32)" << end();
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}
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uint8_t index = (sib>>3)&0x7;
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if (index == ESP) {
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// ignore index and scale
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trace(2, "run") << "effective address is 0x" << std::hex << addr << end();
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}
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else {
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uint8_t scale = (1 << (sib>>6));
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addr += Reg[index].i*scale; // treat index register as signed. Maybe base as well? But we'll always ensure it's non-negative.
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trace(2, "run") << "effective address is 0x" << std::hex << addr << " (after adding " << rname(index) << "*" << NUM(scale) << ")" << end();
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}
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return addr;
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}
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:(scenario add_r32_to_mem_at_base_r32_index_r32)
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% Reg[3].i = 0x10; // source
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% Reg[0].i = 0x5e; // dest base
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% Reg[1].i = 0x2; // dest index
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% SET_WORD_IN_MEM(0x60, 1);
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# op ModR/M SIB displacement immediate
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01 1c 08 # add EBX to *(EAX+ECX)
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# ModR/M in binary: 00 (indirect mode) 011 (src EBX) 100 (dest in SIB)
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# SIB in binary: 00 (scale 1) 001 (index ECX) 000 (base EAX)
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+run: add EBX to r/m32
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+run: effective address is initially 0x5e (EAX)
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+run: effective address is 0x60 (after adding ECX*1)
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+run: storing 0x00000011
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:(scenario add_r32_to_mem_at_displacement_using_sib)
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% Reg[3].i = 0x10; // source
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% SET_WORD_IN_MEM(0x60, 1);
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# op ModR/M SIB displacement immediate
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01 1c 25 60 00 00 00 # add EBX to *0x60
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# ModR/M in binary: 00 (indirect mode) 011 (src EBX) 100 (dest in SIB)
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# SIB in binary: 00 (scale 1) 100 (no index) 101 (not EBP but disp32)
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+run: add EBX to r/m32
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+run: effective address is initially 0x60 (disp32)
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+run: effective address is 0x60
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+run: storing 0x00000011
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