Slide 4.8: .CODE, .DATA, .STACK, and PROC directives

.CODE, .DATA, .STACK, & PROC Directives

Assembly programs are organized around segments, which are usually named code, data, and stack:

.CODE identifies the area of a program that contains instructions.
.DATA identifies the area of a program that contains variables.
.STACK, which can be hidden by using INCLUDE Irvine32.inc, holds procedure parameters and local variables.

The code segment contains one or more procedures, with one designated as the startup procedure. PROC identifies the beginning of a procedure, e.g.,

   main PROC

where the procedure name is main, which is also the startup procedure.

WriteString (textbook page 124)

It writes a null-terminated string to standard output. When calling it, place the string's offset in EDX register. The hexadecimal bytes 0Dh and 0Ah are end-of-line characters.


 .data
 book  BYTE  "MASM Assembler", 0
 .code
 mov   edx, OFFSET book
 call  WriteString


 .data
 hexVal  DWORD   ?
 .code
 call    ReadHex
 mov     hexVal, eax

ReadHex (textbook page 121)
It reads a 32-bit hexadecimal integer from standard input, terminated by the Enter key, and returns the value in EAX register.

WriteHex (textbook pages 123 – 124)
It writes a 32-bit unsigned integer to standard output in 8-digit hexadecimal format. Leading zeros are inserted if necessary. Before calling it, place the integer in EAX register.


 .data
 X  DWORD  50000h
 .code
 mov   eax, X
 call  WriteHex