when compiling the instruction
movl 4(%ebp), 8(%ebp)
i got 'too many memory referene', what's wrong with it??
+1
A:
It is not a legal instruction. For most instructions that reference memory you must move it to/from a register.
GregS
2010-03-28 02:30:56
+1
A:
movl doesn't to memory-memory moves, you have to go by way of a register (thus with two movl instructions).
Alex Martelli
2010-03-28 02:31:27
thanks, but why this? is the cpu archtecture that limit this or something else?
freenight
2010-03-28 02:34:38
Yes, it's a limitation in the CPU. MOVS is about the only memory-to-memory instruction.
Jerry Coffin
2010-03-28 02:46:26
Yeah, memory-to-memory just can't be implemented all that efficiently (non-x86 CPUs tend to have all instructions be just register to register, with load/store as the only register-to-memory ones).
Alex Martelli
2010-03-28 03:02:21
+2
A:
The number before the parenthesis is a byte offset (which causes a memory reference to occur), and you cannot have two of them with movl. You need to move the value temporarily to a register first.
movl 4(%ebp), %ecx
movl %ecx, 8(%ebp)
Marc W
2010-03-28 02:31:35