Bryand and O'Hallaron
                             Chapter 3 Section 4.2
                                 Data Movement



Data Movement Instructions

The various "mov" instructions are two operand instructions with the IA-32
restriction that both operands cannot be in memory.

Instruction         Effect                     Description

movl     S, D       D <- S                     Move double word
movw     S, D       D <- S                     Move word
movb     S, D       D <- S                     Move byte

movsbl   S, D       D <- SignExtend(S)         Move sign-extended byte
movsbl   S, D       D <- ZeroExtend(S)         Move zero-extended byte

pushl    S          R[%esp] <- R[%esp] - 4     Push   
                    M[R[%esp]] <- S

popl     S          D <- M[R[%esp]]            Push   
                    R[%esp] <- R[%esp] + 4


Examples

1    movl $0x4050,%eax            #Immediate--Register
2    movl %ebp,%esp               #Register--Register
3    movl (%edi,%ecx),%eax        #memory--Register
4    movl $17,(%esp)              #immediate--Memory
5    movl %eax,-12(%ebp)          #Register--Memory



Comparing Byte Movement Instructions

assume that %dh = 0x8D, %eax = 0x98765432

1   movb    %dh,%al              # %eax = 0x9876548D
2   movb    %dh,%ah              # %eax = 0x98768D32
3   movsbl  %dh,%eax             # %eax = 0xFFFFFF8D
4   movsbl  %dh,%eax             # %eax = 0x0000008D


Push and pop operations

           push  longthing                       pop longthing
   ;equivalent code                      ;equivalent code
           subl  $4,%esp                         movl  (%esp),longthing
           movl  longthing,(%esp)                addl  $4,%esp


  address    memory (the stack)            %esp 
 
            +-----------------+ 
0xbffffffc  |                 |<------  20(%esp)
            +-----------------+ 
0xbffffff8  |                 |<------  16(%esp)
            +-----------------+ 
0xbffffff4  |                 |<------  12(%esp)
            +-----------------+ 
0xbffffff0  |       third pop |<------   8(%esp)
            +-----------------+ 
0xbfffffec  |      second pop |<------   4(%esp)
            +-----------------+        +-----------------+ 
0xbfffffe8  |       first pop |<------ |                 | %esp 
            +-----------------+        +-----------------+
0xbfffffe4  |      first push |<------  -4(%esp)
            +-----------------+ 
0xbfffffe0  |     second push |<------  -8(%esp)
            +-----------------+ 
0xbfffffdc  |      third push |<------ -12(%esp)
            +-----------------+ 
0xbfffffd8  |                 |<------ -16(%erg)
            +-----------------+ 
0xbfffffd4  |                 |<------ -20(%esp)
            +-----------------+