MOVing between two memory addresses

assembly x86 instructions mov
Justin picture Justin · Aug 19, 2009 · Viewed 37.9k times · Source

I'm trying to learn assembly (so bear with me) and I'm getting a compile error on this line:

mov byte [t_last], [t_cur]

The error is

error: invalid combination of opcode and operands

I suspect that the cause of this error is simply that its not possible for a mov instruction to move between two memory addresses, but half an hour of googling and I haven't been able to confirm this - is this the case?

Also, assuming I'm right that means I need to use a register as an intermediate point for copying memory:

mov cl, [t_cur]
mov [t_last], cl

Whats the recommended register to use (or should I use the stack instead)?

Answer

Federico klez Culloca picture Federico klez Culloca · Aug 19, 2009

Your suspicion is correct, you can't move from memory to memory.

Any general-purpose register will do. Remember to PUSH the register if you are not sure what's inside it and to restore it back once done.

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