Assembly language is a low-level programming language that allows direct control over a computer’s hardware. In this article, we will explore the structure and syntax of assembly language programs, including the division into three sections: data, bss, and text. We will also examine the syntax of assembly language statements and provide an example of a “Hello World” program.
The Data Section:The data section is used for declaring initialized data or constants that remain unchanged during program execution. This section is defined using the syntax: section .data. It is where you declare variables, constants, or other data values.
The bss Section:The bss section is used for declaring variables that need memory allocation but don’t require initialization. It is defined using the syntax: section .bss. This section is commonly used to reserve memory space for variables that will be assigned values later in the program.
The Text Section:The text section contains the actual code of the program. It begins with the declaration “global _start,” which indicates the entry point for program execution. The syntax for defining the text section is: section .text.
Comments:Assembly language allows comments to provide explanatory notes within the code. Comments start with a semicolon (;) and can appear on a separate line or alongside an instruction. They help improve code readability and understanding.
Assembly Language Statements:
Assembly language programs consist of three types of statements:
Executable Instructions: These instructions tell the processor what to do and generate machine language instructions.
Assembler Directives or Pseudo-ops: These non-executable statements provide information to the assembler about the assembly process.
Macros: Macros are used for text substitution and are not executable instructions themselves.
Syntax of Assembly Language Statements:
Assembly language statements follow a specific format: [label] mnemonic [operands] [;comment]. Labels and comments are optional. Instructions consist of a mnemonic (instruction name) followed by operands (parameters) for the instruction.
Example: “Hello World” Program in Assembly:
We provide an example of a simple “Hello World” program in assembly language. The code demonstrates how to display the string “Hello, world!” on the screen using system calls. It includes sections for data and text, along with the necessary system call instructions.
Compiling and Linking an Assembly Program:
The article concludes with instructions on how to compile and link an assembly program using the NASM assembler. It outlines the steps to create an object file and then link it to generate an executable file.
Understanding the structure and syntax of assembly language programs is essential for writing efficient and low-level code. By grasping the concept of sections, syntax of statements, and the use of comments, programmers can develop powerful software solutions that interact directly with hardware.