TEMPLATE

RAM SEGMENTS

• Stack: Local variables and function call management; grows downwards.

  • To easily visualize how the call stack grows in memory, imagine an icicle forming on a rooftop. The rooftop represents high memory addresses (e.g., 0xFFFFFF), while the tip of the icicle represents low memory addresses. As water drips and freezes, the icicle grows downward, extending farther from the roof. The stack behaves the same way: each new function call pushes (adds) a new stack frame downward (lower) in memory, toward lower addresses, just like an icicle lengthening toward its tip.

• Heap: Dynamically allocated memory (e.g., via malloc); grows upwards.

• .bss (block started by symbol - READ/WRITE): Stores uninitialized global/static variables (they get zero-initialized by OS).

• .data (initialized data - READ/WRITE - NOT EXECUTABLE): Stores initialized global and static variables.

• .text (code section - READ-ONLY - EXECUTABLE): Contains program instructions; usually at the lowest addresses.

X86: GCC METHOD

;*######################################################################################
; Dev: cnd.dev
; Program Name: FileName-v1.0.0-linux-x86-64
; Version: 1.0.0                                               //Major.Minor.Update
; Date: 181445MAR25
; Filename: filename.c
; Dependency: N/A
; Compile Cmd: gcc -m64 -O1 filename.c -o filename-v1.0.0-linux-x86-64
; Synopsis: ...
;  - Overview: describes what the program does, how it works, and its key components
;  - Technical: ...
;#####################################################################################*/

;INCLUDE FILES

section .bss
    ; uninitialized data

section .data
    ; initialized data

section .text
    global _start                              ; Entry point for the program (used by linker)

  _start:
    
    ; ********** FUNCTION PROLOGUE *********
    push	ebp                            ; Save base pointer of the previous stack frame
    mov		ebp, esp                       ; Establish a new stack frame for this function
    ; ********** CODE STARTS HERE **********

  end:
  
    ; *********** CODE ENDS HERE ***********
    mov		eax, 0                          ; Set return value to 0 (success)
    mov		esp, ebp                        ; Restore original stack pointer
    pop		ebp                             ; Restore previous base pointer
    ret                                         ; Return from _start (only valid if this is called as a function)

X64: NASM METHOD

;*######################################################################################
; Dev: cnd.dev
; Program Name: FileName-v1.0.0-linux-x86-64
; Version: 1.0.0                                               ; Major.Minor.Update
; Date: 181445MAR25
; Filename: filename.asm
; Dependency: N/A
; Compile Cmd: nasm -f elf64 filename.asm -o filename.o && ld filename.o -o filename-v1.0.0-linux-x86-64
; Synopsis:
;  - Overview: describes what the program does, how it works, and its key components
;  - Technical: ...
;######################################################################################*/

; SECTION: INCLUDE FILES
; Declare printf as an external function (from libc)

section .bss
    ; Uninitialized data (e.g., buffers, counters)

section .data
    ; Initialized data (e.g., strings, format specifiers)

; Code section (actual instructions)
section .text
    ; Make the _start label visible to the linker
    global _start
    
; Entry point of the program
_start:
    ; ********** CODE STARTS HERE **********
    
    ; Example: write "Hello\n" to stdout
    mov     rax, 1          ; syscall: write
    mov     rdi, 1          ; file descriptor: stdout
    mov     rsi, message    ; pointer to message
    mov     rdx, message_len ; message length
    syscall

    ; Exit
    mov     rax, 60         ; syscall: exit
    xor     rdi, rdi        ; status: 0
    syscall

    ; *********** CODE ENDS HERE ***********

; SECTION: DATA

section .data
    message     db "Hello, world!", 10
    message_len equ $ - message

X64: W/ FUNCTIONS

The ordering of section directives in my assembly source may differ from the conventional .data, .bss, .text layout typically used by others. This is intentional, as the arrangement serves purely as a visualization aid. Placing .bss, .data, and .text in a custom order helps me mentally associate each memory section with my own conceptual model of how a program is represented in memory. Although the assembler and linker ultimately determine the true physical layout, organizing the sections in a way that aligns with my personal understanding allows me to more clearly internalize how each region is defined, how they differ in purpose, and how they relate to one another within a process’s memory space. This approach enhances my comprehension while leaving the actual binary structure unchanged.

extern printf
section .bss
section .data
      radius      dq    10.0
section .text
;----------------------------------------------
area:
      section .data
            .pi  dq    3.141592654      ; local to area
      section .text
push  rbp
mov   rbp, rsp
      movsd      xmm0, [radius]
      mulsd      xmm0, [radius]
      mulsd      xmm0, [.pi]
leave
ret
;----------------------------------------------
circum:
section .bss
section .data
      .pi  dq     3.14        ; local to circum
section .text
push  rbp
mov   rbp, rsp
      movsd       xmm0, [radius]
      addsd       xmm0, [radius]
      mulsd       xmm0, [.pi]
leave
ret
;----------------------------------------------
circle:
section .bss
section .data
      .fmt_area  db    "The area is %f",10,0
      .fmt_circum      db    "The circumference is %f",10,0
section .text
push  rbp
mov   rbp, rsp
      call  area
      mov   rdi,.fmt_area
      mov   rax,1            ; area in xmm0
      call  printf
      call  circum
      mov   rdi,.fmt_circum
      mov   rax,1            ; circumference in xmm0
      call  printf
leave
ret
;----------------------------------------------
      global main
main:
push  rbp
mov   rbp, rsp
      call  circle
leave
ret