diff options
Diffstat (limited to 'subx/011add.cc')
-rw-r--r-- | subx/011add.cc | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/subx/011add.cc b/subx/011add.cc new file mode 100644 index 00000000..b84797d1 --- /dev/null +++ b/subx/011add.cc @@ -0,0 +1,46 @@ +:(scenario add_r32_to_rm32) +% Reg[3].i = 0x10; +% Reg[0].i = 0x60; +# word in addresses 0x60-0x63 has value 1 +% Mem[0x60] = 1; +# op ModR/M SIB displacement immediate + 01 18 # add EBX to *EAX ++run: add register 3 to effective address ++run: effective address is memory at address 0x60 (register 0) ++run: storing 0x11 + +:(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 register " << static_cast<int>(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 'register 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(99, "run") << "effective address is memory at address 0x" << std::hex << Reg[rm].u << " (register " << static_cast<int>(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 + } + return result; +} |