printing_strings_to_terminal

ARM Assembly Printing Strings to Terminal

Welcome to your Raspberry Pi linux terminal. If you're here, you've successfully connected via SSH using ssh pi@127.0.0.1 -p 5022. If you're unsure about the setup process, please refer to the previous notes on setting up QEMU for ARM here.

Writing the Code

Open the helloworld.s file in the nano editor:

nano helloworld.s

Here's the helloworld.s ARM assembly code:

.global _start
_start:
        MOV R0,#1
        LDR R1,=message
        LDR R2,=len
        MOV R7,#4
        SWI 0

        MOV R7,#1
        SWI 0

.data
message:
        .asciz "radhe radhe \n"
len = .-message

Code Explanation

• .global _start: Marks the _start label as global, making it visible to the linker.
• _start:: The entry point of our program.
• MOV R0,#1: Moves the value 1 into register R0, which is used for file descriptor (stdout).
• LDR R1,=message: Loads the address of the message label into register R1.
• LDR R2,=len: Loads the address of the len label into register R2.
• MOV R7,#4: Moves the value 4 into register R7, which is the system call number for 'write'.
• SWI 0: Triggers an interrupt to invoke a system call.
• .data: Indicates that what follows is data (not code).
• message:: A label marking where our message starts.
• .asciz "radhe radhe \n": Defines a null-terminated string.
• len = .-message: Defines the length of our message.

Compiling and Running

Compile the assembly code into an object file:

as helloworld.s -o helloworld.o

Link the object file to create an executable:

ld helloworld.o -o helloworld

Verify that all files are present:

ls

Run your executable:

./helloworld

You should see the output:

radhe radhe