What are the most common Arm assembly language programming instructions?

Arm assembly language is a low-level programming language that directly controls the hardware of Arm-based devices, such as smartphones, tablets, and embedded systems. It allows programmers to manipulate data, registers, memory, and input/output devices with precise and efficient instructions. In this article, we will introduce some of the most common Arm assembly language programming instructions and how they work.

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1 Data Processing Instructions

Data processing instructions are used to execute arithmetic, logical, and bitwise operations on data stored in registers or immediate values. Examples of such instructions include ADD, which adds two operands and stores the result in a destination register; SUB, which subtracts the second operand from the first and stores the result in a destination register; AND, which performs a bitwise AND operation on two operands and stores the result in a destination register; ORR, which performs a bitwise OR operation on two operands and stores the result in a destination register; MOV, which copies the value of one operand to a destination register; and CMP, which compares two operands and sets the condition flags according to the result.

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Sanjay Guha

Material Handler at ARaymond Network
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Data processing instructions show how data is read by adding or subtracting numerical operands, moving operands, comparing operands, and performing logical operations on these operands.

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Alex Lim

Software Engineer at Google
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Data processing instructions allow you to perform arithmetic, logical, and bitwise operations on data. An important thing to keep track of is if the numbers are signed and how they're being represented. For example, if you treat a floating point number as an integer or vice versa, you may have a valid number, but it will not be the same number that you started with.

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2 Load and Store Instructions

Load and store instructions are used to transfer data between registers and memory, as well as access input/output devices by using special memory addresses. Examples of such instructions include LDR, which loads a word (32 bits) from a memory address into a register, and STR, which stores a word (32 bits) from a register into a memory address. Additionally, there are LDRB and STRB for loading and storing bytes (8 bits), as well as LDRH and STRH for loading and storing halfwords (16 bits).

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Krunal Dabhi

Technical Project Manager - Efficiently and successfully leading multi-million dollar infrastructure
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Instructions for loading and storing data are employed to move information between registers and memory, as well as interact with input/output devices via specific memory addresses. For instance, the LDR instruction retrieves a word (32 bits) from a memory address into a register, while the STR instruction stores a word from a register into a memory address. Moreover, there are specialized instructions like LDRB and STRB for handling bytes (8 bits), as well as LDRH and STRH for managing halfwords (16 bits).

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3 Branch Instructions

Branch instructions are used to alter the flow of execution by transitioning to a different location in the program. Depending on the condition flags, these instructions can be either conditional or unconditional. For instance, B branches unconditionally to a label or an offset, BL branches unconditionally to a label or an offset and saves the return address in the link register (LR), BX branches unconditionally to an address stored in a register and switches the instruction set if needed, BEQ branches conditionally to a label or an offset if the zero flag (Z) is set, BNE branches conditionally to a label or an offset if the zero flag (Z) is not set, and BGT branches conditionally to a label or an offset if the greater than flag (GT) is set.

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Alex Lim

Software Engineer at Google
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Branching is used to alter how program is executed by transitioning to a different part of the program. You may also see this referred to as "Jumping". Let's go over the most common and basic branch instructions in ARM. Branch (B) is used for unconditional branching where you will always jump to a specific location in the program. Conditional Branch (ie: BEQ) is used for branching if the condition is met (ie: is equal to). Branch with Link (BL) is used to perform a subroutine call where the next instruction's address is stored in the link register (LR). Branch and Exchange (BX) is used to perform a branch where the instruction set may be different, usually swapping between ARM Mode which is 32 bits to Thumb Mode which is 16 bits.

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4 Software Interrupt Instructions

Software interrupt instructions are used to invoke system services or routines provided by the operating system or the firmware. These instructions can be used to conduct tasks such as input/output, memory management, process control, and exception handling. Common Arm assembly language programming instructions include SVC, which invokes a system call with a specified number; BKPT, which causes a breakpoint exception for debugging purposes; HVC, which invokes a hypervisor call with a specified number; and SMC, which invokes a secure monitor call with a specified number. To gain more knowledge about Arm assembly language programming, you can consult the official documentation or online tutorials.

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Alex Lim

Software Engineer at Google
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Software interrupt instructions are used to trigger software interrupts as the name implies. This is commonly used for system calls and exception handling. The Software Interrupt (SWI) instruction is commonly used for this purpose in order to trigger a system call.

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5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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What are the most common Arm assembly language programming instructions?

1

2

3

4

5

1 Data Processing Instructions

2 Load and Store Instructions

3 Branch Instructions

4 Software Interrupt Instructions

5 Here’s what else to consider

Computer Hardware

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What are the most common Arm assembly language programming instructions?

1

2

3

4

5

1 Data Processing Instructions

2 Load and Store Instructions

3 Branch Instructions

4 Software Interrupt Instructions

5 Here’s what else to consider

Computer Hardware

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