x86 instruction format is:
[label:] mnemonic [operands][ ;comment ]
Number of operands included in the instruction can be: 0, 1, 2 or 3. Here, for clarity, reference numerals and omitted Notes:
mnemonic
mnemonic [destination] mnemonic [destination] , [source] mnemonic [destination] , [source-1] , [source-2]
Operands are three basic types:
- Immediate - digital text expression
- Register operand - using the CPU registers named
- Memory operand - referenced memory location
The following table illustrates the types of operands standard, which uses a simple operand symbol (32-bit mode), the symbols from Intel and a manual adaptation. This tutorial syntax of these symbols to describe each instruction.
| Number of operations | Explanation |
|---|---|
| reg8 | 8 general-purpose registers: AH, AL, BH, BL, CH, CL, DH, DL |
| Regl6 | 16-bit general purpose registers: AX, BX, CX, DX, SI, DI, SP, BP |
| reg32 | 32-bit general purpose registers: EAX, EEX, ECX, EDX, ESI, EDI, ESP, EBP |
| reg | General-purpose registers |
| comfortable | 16-bit segment register: CS, DS, SS, ES, FS, GS |
| imm | 8, 16-bit or 32-bit immediate data |
| imm8 | 8, immediate byte value |
| imm16 | 16, immediate word values |
| imm32 | 32-bit immediate data, double word value |
| reg/mem8 | 8 operand may be an 8-bit general purpose registers or memory byte |
| reg/mem16 | 16-bit immediate data may be a 16 bit general purpose register or a memory word |
| reg/mem32 | 32-bit immediate which can be 32-bit double word general register or memory |
| mem | 8, 16-bit or 32-bit memory operand |
Direct memory operand
Reference to the variable name is the offset within the data segment. For example, the following declaration of variables varl indicates the size of the variable type byte hexadecimal value 10:
.data var1 BYTE 10h
You can write command, the address of the memory operand to resolve (find) these operands. Suppose var1 offset address 10400h. The following command to copy the value of the variable register AL:
mov al var1
Instruction is compiled into the following machine instructions:
A0 00.0104 million
This first byte is the operation code of the machine instruction (i.e. an operation code (opcode)). Var1 remainder being 32-bit hexadecimal address. While programming is possible using only numeric addresses, but the same sign as var1 labels will make it easier to use memory.
Another notation. Some programmers prefer to use such a direct expression operand below, because, braces means parsing operation:
mov al, [var1]
MASM allow this representation, so as long as you are willing to be used in the program. Since most programs (including Microsoft program) are not printed in parentheses, so the book only in the event of representation when using this arithmetic expressions with parentheses:
mov al, [var1 + 5]
Next: MOV instruction
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