1: / define numeric label "1"
one: / define symbolic label "one"
/ ... assembler code ...
jmp 1f / jump to first numeric label "1" defined
/ after this instruction
/ (this reference is equivalent to label "two")
jmp 1b / jump to last numeric label "1" defined
/ before this instruction
/ (this reference is equivalent to label "one")
1: / redefine label "1"
two: / define symbolic label "two"
jmp 1b / jump to last numeric label "1" defined
/ before this instruction
/ (this reference is equivalent to label "two")
2.There are fve classes of tokens:
■ Identifers (symbols)
■ Keywords
■ Numerical constants
■ String Constants
■ Operators
3.An x86 instruction statement can consist of four parts:
■ Label (optional)
■ Instruction (required)
■ Operands (instruction specifc)
■ Comment (optional)
4.Possible operand types and their instruction sufxes are:b Byte (8–bit)w Word (16–bit)
l Long (32–bit) (default)
q Quadword (64–bit)
5.Only jump and call
instructions can use indirect operands.
Immediate operands are prefxed with a dollar sign ($) (ASCII 0x24)
■ Register names are prefxed with a percent sign (%) (ASCII 0x25)
■ Memory operands are specifed either by the name of a variable or by a register that contains
the address of a variable. A variable name implies the address of a variable and instructs the
computer to reference the contents of memory at that address. Memory references have the
following syntax:
segment:offset(base, index, scale).
■ Segment is any of the x86 architecture segment registers. Segment is optional: if specifed,
it must be separated from offset by a colon (:). If segment is omitted, the value of %ds (the
default segment register) is assumed.Offset is the displacement from segment of the desired memory value. Offset is optional.■ Base and index can be any of the general 32–bit number registers.■ Scale is a factor by which index is to be multipled before being added to base to specify
the address of the operand. Scale can have the value of 1, 2, 4, or 8. If scale is not specifed,
the default value is 1.
movl var, %eax
-->Move the contents of memory location var
into number register %eax.
movl %cs:var, %eax
-->Move the contents of memory location var
in the code segment (register %cs) into
number register %eax.
movl $var, %eax
-->Move the address of var into number
register %eax.
movl array_base(%esi), %eax
-->Add the address of memory location
array_base to the contents of number
register %esi to determine an address in
memory. Move the contents of this address
into number register %eax.
movl (%ebx, %esi, 4), %eax
-->Multiply the contents of number register
%esi by 4 and add the result to the contents
of number register %ebx to produce a
memory reference. Move the contents of
this memory location into number register
%eax.
movl struct_base(%ebx, %esi, 4), %eax
-->Multiply the contents of number register
%esi by 4, add the result to the contents of
number register %ebx, and add the result to
the address of struct_base to produce an
address. Move the contents of this address
into number register %eax.