3.1 Standard Data Types

C declaration   Intel data type   GAS suffix   Size (bytes)

char            Byte                  b             1
short           Word                  w             2
int             Double Word           l             4
unsigned        Double Word           l             4
long int        Double Word           l             4
unsigned long   Double Word           l             4
char *          Double Word           l             4
float           Single Precision      s             4
double          Double Precision      l             8
long double     Extended Precision    t           10/12


3.2 Integer registers (note the 24 different names)

bit  31                              15              7             0
    +-------------------------------+---------------+---------------+
%eax|                               |      %ah      |      %al      |%ax
    +-------------------------------+---------------+---------------+
%ecx|                               |      %ch      |      %cl      |%cx
    +-------------------------------+---------------+---------------+
%edx|                               |      %dh      |      %dl      |%dx
    +-------------------------------+---------------+---------------+
%ebx|                               |      %bh      |      %bl      |%bx
    +-------------------------------+---------------+---------------+
%esi|                               |                               |%si
    +-------------------------------+-------------------------------+
%edi|                               |                               |%di
    +-------------------------------+-------------------------------+
%esp|                               |                               |%sp
    +-------------------------------+-------------------------------+
%ebp|                               |                               |%bp
    +-------------------------------+-------------------------------+


Status Registers

    +-------------------------------+-------------------------------+
%eip|                               |                               |%ip
    +-------------------------------+-------------------------------+

    +-------------------------------+-------------------------------+
eflg|                               |                               |flg
    +-------------------------------+-------------------------------+


Operand Forms

Type       Form                Operand value                 Name

Immediate  $Imm                Imm                           Immediate
Register   %reg                R[reg]                        Register
Memory     Imm                 M[Imm]                        Absolute
Memory     (%reg)              M[R[reg]]                     Indirect
Memory     Imm(%reg)           M[Imm + R[reg]]               Base + displacement
Memory     (%reg, %reg)        M[R[reg] + R[reg]]            Indexed
Memory     Imm(%reg, %reg)     M[Imm + R[reg] + R[reg]]      Indexed
Memory     (, %reg, s)         M[R[reg] * s]                 Scaled index
Memory     (Imm, %reg, s)      M[Imm + R[reg] * s]           Scaled index
Memory     (%reg, %reg, s)     M[R[reg] + R[reg]*s]          Scaled index
Memory     Imm(%reg, %reg, s)  M[Imm + R[reg] + R[reg]*s]    Scaled index


Data Movement Instructions

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
movzbl  S, D          D <- ZeroExtend(S)        Move zero-extended byte
pushl   S             R[%esp] <- R[%esp] - 4    Push
                      M[R[%esp]] <- S
popl    D             D <- M[R[%esp]]           Pop
                      R[%esp] <- R[%esp] + 4   


Examples

movl    $0x4050,%eax
movl    %ebp,%esp
movl    (%edi,%ecx),%eax
movl    $-17,(%esp)
movl    %eax,-12(%ebp)
movb    $0x80,%al
movsbl  $0x80,%eax
movzbl  $0x80,%eax

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