4.6: Text Section
- Page ID
- 19881
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The code is placed in the "section .text" section. There must be a space after the word 'section'. The instructions are specified one per line and each must be a valid instruction with the appropriate required operands.
The text section will include some headers or labels that define the initial program entry point. For example, assuming a basic program using the standard system linker, the following declarations must be included.
global _start
_start:
No special label or directives are required to terminate the program. However, a system service should be used to inform the operating system that the program should be terminated and the resources, such as memory, recovered and re-utilized. Refer to the example program in the following section.
A very simple assembly language program is presented to demonstrate the appropriate program formatting.
; Simple example demonstrating basic program format and layout.
; Ed Jorgensen ; July 18, 2014
; ************************************************************ ; Some basic data declarations
section .data
; ----- ; Define constants
EXIT_SUCCESS equ 0 ; successful operation SYS_exit equ 60 ; call code for terminate
; ----- ; Byte (8-bit) variable declarations
bVar1 db 17 bVar2 db 9 bResult db 0
; ----- ; Word (16-bit) variable declarations
wVar1 dw 17000 wVar2 dw 9000 wResult dw 0
; ----- ; Double-word (32-bit) variable declarations
dVar1 dd 17000000 dVar2 dd 9000000 dResult dd 0
; ----- ; quadword (64-bit) variable declarations
qVar1 dq 170000000 qVar2 dq 90000000 qResult dq 0
; ************************************************************ ; Code Section
section .text global _start _start:
; Performs a series of very basic addition operations ; to demonstrate basic program format.
; ---------- ; Byte example ; bResult = bVar1 + bVar2
mov al, byte [bVar1]
add al, byte [bVar2]
mov byte [bResult], al
; ---------- ; Word example ; wResult = wVar1 + wVar2
mov ax, word [wVar1]
add ax, word [wVar2]
mov word [wResult], ax
; ---------- ; Double-word example ; dResult = dVar1 + dVar2
mov eax, dword [dVar1]
add eax, dword [dVar2]
mov dword [dResult], eax
; ---------- ; Quadword example ; qResult = qVar1 + qVar2
mov rax, qword [qVar1]
add rax, qword [qVar2]
mov qword [qResult], rax
; ************************************************************ ; Done, terminate program.
last:
mov rax, SYS_exit ; Call code for exit
mov rdi, EXIT_SUCCESS ; Exit program with success
syscall
This example program will be referenced and further explained in the following chapters.