Contents
How many bytes is a mov instruction?
4 bytes
Addressing Memory
| mov eax, [ebx] | ; Move the 4 bytes in memory at the address contained in EBX into EAX |
|---|---|
| mov [var], ebx | ; Move the contents of EBX into the 4 bytes at memory address var. (Note, var is a 32-bit constant). |
| mov eax, [esi-4] | ; Move 4 bytes at memory address ESI + (-4) into EAX |
Does mov clear register?
mov does break the dependency chain on the old value of the register (regardless of the source value, zero or not, because that’s how mov works).
What is the opcode for mov?
“mov” is an instruction, encoded with the operation code or “opcode” 0xb8. Since mov takes an argument, the next 4 bytes are the constant to move into eax. The opcode 0xb9 moves a constant into ecx. 0xba moves a constant into edx.
Is the MOV instruction Turing complete?
Yes, x86’s mov is Turing complete.
Does MOV copy or move?
Many processors have an instruction called “move” (sometimes spelled MOV) which copies data from one location (the “source”) to another (the “destination”) in registers and/or memory. It does not do anything to the “source”. This is analogous to the “copy” (or “cp”) command in a filesystem.
What is MOV in COA?
In 8085 Instruction set, MOV is a mnemonic, which stands for “MOVe”. In this instruction 8-bit data value in register r2 will be moved to the 8-bit register r1.
What are MOV instructions with byte destination for immediate to?
As another example, consider mov BYTE PTR [edx], -1 with the memory destination using register indirect mode. The opcode is still C6 and the immediate byte (which always comes last) is now FF for -1. The second byte is the ModR/M byte with Mod=00 for register indirect, Reg=000 (unused), and R/M=010 for EDX, making 00 000 010 or 02.
How many bytes does MOV smallcounter, 100 generate?
If, for example, smallCounter references a byte in memory and the instruction mov smallCounter, 100 is assembled, the assembler will generate 7 (3+4) bytes of object code, C6 05 xx xx xx xx 64, where xx xx xx xx represents the address in memory, and 64 is the byte-size hex version of 100.
What are the registers in assembly addressing mode?
This addressing mode utilizes the computer’s ability of Segment:Offset addressing. Generally, the base registers EBX, EBP (or BX, BP) and the index registers (DI, SI), coded within square brackets for memory references, are used for this purpose.
How to move data from memory to a general purpose register?
I can move data items stored in memory, to a general-purpose register of my choosing, using the MOV instruction. Now, don’t shoot me, but how is the following achieved: MOV r24, [m24]? (I appreciate the latter is not legal). In my example, I want to move the characters “Pip”, i.e. 0x706950h, to register rax.