Assemble for ARM with GNU Assembler

Introduction to the GNU Assembler in ARM Architecture

The GNU Assembler (GAS) is a powerful command-line tool for creating and managing the assembly language code used in ARM architectures. GAS is an open source offering, distributed with the GNU Compiler Collection (GCC) and commonly used with Embedded Linux systems.

When compiling programs in ARM architecture, GAS provides an assembler pre-processor, macro capabilities, and support for several object file formats. It also includes a debugger for running and debugging applications written in ARM assembly.

Understanding the GAS Syntax

Before you can use GAS to assemble ARM assembly code, it is important to understand the syntax of the assembly language. GAS syntax follows the same basic rules as other architectures. It uses mnemonics to represent instructions. Each mnemonic includes the instruction type, a list of operand registers or memory locations, and other modifiers depending on the instruction type.

For example, if we wanted to move a value from a register to another register, the instruction would look like this: MOV R1,R2. Here, the mnemonic is MOV, and the operands are R1 and R2.

Using GAS to Assemble ARM Code

Once you are familiar with the syntax of GAS, you can begin writing and assembling ARM assembly code with it. To create an object file, use the following command:

$ as [options] input-file [output-file]

The options flag is optional, and can be used to control the output format, code generation, debugging, and more. You can find a full list of available options in the GAS documentation.

Debugging Applications with GAS

GAS includes a built-in debugger for debugging applications written in ARM assembly. To debugging using GAS, you first need to create a debug-info file by compiling your program with the -g option. This file contains information about the program, such as line numbers and variable names.

Once the debug-info file is created, you can launch the GAS debugger by running the following command:

$ gdb [options] input-file [debug-info-file]

The options flag is optional, and can be used to specify things such as breakpoints, watches, and source files. You can find more information about GAS debugger options in the GAS documentation.

Conclusion

GAS is an incredibly powerful and versatile tool for creating and managing assembly language code for ARM architectures. Its syntax is easy to learn, and it includes several features for controlling code generation and debugging. GAS is open source and freely available, making it an ideal choice for any ARM assembly projects.