What is the shortest way to fetch a value from memory in X86 Assembler?
I just want the shortest way to get a value from memory into a CPU register. I don't mind which way...
Tony
2010-03-30 22:15:00
well, that's it
klez
2010-03-30 22:18:53
Assuming you're using Intel syntax you won't find a shorter or faster way than that. I'm not sure how to put this delicately... if you had to ask that question, I would strongly recommend getting a book on assembly language fundamentals before you go any further.
Dan Story
2010-03-30 22:23:39
+1
A:
OK, the shortest way is to pop registers, like pop eax, it's one byte instruction.
But that can be used only in special cases, where the stack pointer ESP will point to a buffer,
and probably you won't use the stack for other purpose until the code that uses it is done.
The standard way is to use the mov instruction.
Nick D
2010-03-30 22:35:40
+3
A:
There is no workaround in assembler haw to do that. All assembler instructions are strictly dedicated.
mov AL, 0x12
will load immediate the value 0x12 to register AL
xor AL,AL
the result of operation in AL register is 0
lodsb
will load byte from DS:[ESI] (or DS:[SI] under 16 bit CPU) memory address to AL
mov AL,[ESI]
will load byte from DS:[ESI] (or DS:[SI] under 16 bit CPU) memory address to AL
mov AL,[0xFFFF]
will load byte from DS:[0xFFFF] memory address to AL
pop AX
will load byte from SS:[ESP] (or SS:[SP] under 16 bit CPU) memory address to AL
in AL, 0x123
will load byte from port address 0x123
xlatb [EBX + AL]
will load byte from DS:[EBX + AL] memory address
...
GJ
2010-03-31 06:20:39