On the issue of the compilation of the LEA Directive

mov ecx, [eax+0x30] means that the first operation of eax+0x30 to obtain a result, and use this result as the address to find an ecx length of memory and assign it to ecx

lea ecx, [eax+0x30] means that eax+0x30 first get a result, and assign this result (MOV address) to ECX

The effect is ecx=eax+0x30 (here eax participates in the operation but does not change the value), if you don't use this, then use it.

mov ecx,0x30

add ecx,eax

Judging by the length of the instruction and the speed of execution. lea ecx, [eax+0x30] to be good.

If it succeeds, it will return 0, and if it is wrong, it will return an error message. It depends on what the instructions are later. I estimate that the value returned by EAX may be used as an option, different EAX values print different error messages.

If you dare to be interested in this problem, it is better to test the effect of various values in the case of dynamic tracking.

Hello landlord. What you said about EAX is 0, which is just a special case of this problem, and it is very likely that EAX is not equal to 0. This instruction is universal and beyond the average beginner can write.

Addendum: Versatility lies in the variables of EAX. What if the value returned by the wsastartup function is not 0?

This LEA is often used as an optimization instruction in C++.

Let's take an example.

The next sentence is as long as one always.

lea eax ，[eax+ecx*4+ebx]

The LEA and OFFSET commands are functionally identical, both BX registers can get the value of the symbolic address list, and the MOV instruction will be executed faster than the LEA instruction.

However, an offset can only be connected to a simple symbolic address, not to a complex operand such as list[si] or [si]. Therefore, LEA directives are useful in getting tools to access variables.

offset is the offset address value of the variable or designator that returns the numeric value LEA is the valid address value of the variable or designator SEG, and the assembler returns the segment address value of the variable or designator.

lea is a command of the microcomputer 8086 8088 series, taken from the English loadeffectiveaddress - take the valid address, that is, take the wheel calendar absolute offset address. The instruction format is as follows: LEAREG16, the MEMLEA instruction sends the 4-bit hexadecimal offset address of the memory operand MEM to the register specified by the wildlet kernel.

Here, the source operand must be a memory operand and the destination operand must be a 16-bit general-purpose register. Since this register is often used as an address pointer, it is best to use one of the four address registers BX, BP, SI, and DI. LEA takes the loadeffectiveaddress command format:

leabx, bufferleaax, [bx][di] (j base address plus readdressed addressing) leadx, data[bx][si] (relative base address plus readdressed addressing) The LEA instruction requires that the source operand must be a storage unit, and that the destination operand must be a 16-bit or 32-bit register in addition to the segment register. When the intent operand is.

The lea command is used to load a valid address (loaddffectiveaddress) in the same way as mov. Instead of reading data from a defined location, the instruction writes a valid address into the operandal scatter of the lead-blocking destination. However, it can also succinctly describe ordinary arithmetic operations.

LEA(%rdi,%rsi,1),%EAX is as follows%rdi=>4,%rsi=> socks.

leareg16, mem16 where reg16 must be a 16-bit universal register, mem16 must be a memory, execute this finger as early as the order, the mem16 refers to the 16-bit offset address transmitted to reg16. For example, in the case of LEAAX, the BUFF transmits the address of the BUFF in the memory to AX

lea is the address of the variable.

Another use of LEA is to replace multiplication, such as LEA

EAX, [EAX4+EAX] is faster than using MUL to implement EAX*5.

The function of the LEA instruction is to transfer the source operand, that is, the valid address (offset address) of the memory cell, to the destination operand.

LEA has two operands.

1.On the left is the intent operand, which means that the result of the operation is stored here, and the intent operand of the instruction can only be one of the 8 general-purpose registers.

2.On the right is the source operand, the source operand of the instruction can only be one storage cell, indicating that the storage unit can be addressed in multiple ways.

Example: lea bx, [bx+si+0f54h].

bx+si+0f54h] uses the addressing method of relative base address change to express the memory unit, and the effective address of the storage unit it represents is: bx content plus si content plus 0f54h. This result is transferred to the bx.

leareg16,mem16

where reg16 must be a 16-bit general-purpose coarse memory, mem16 must be a memory, and after executing this instruction, the 16-bit offset address referred to by mem16 will be transmitted to reg16.

For example: LEA

ax,buf

It is to transfer the address referred to by the buf in the memory to ax

Difference MOV Transmission Instructions:

The MOV transmits what the address refers to, while the LEA is just the address.