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MIPS Syscalls

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Index

  1. Introduction
  2. Print Syscalls
  3. Read Syscalls
  4. Exit Syscall

Related

  1. MIPS Assembly MOC

Introduction

Definition

A system call (syscall) in MIPS assembly is a way for a program to request a service from the operating system.

  • The syscall instruction is used, with the type of call specified in the $v0 register. Arguments for the syscall are placed in registers $a0, $a1, $a2, and $a3 as needed. Results are usually returned in $v0 and sometimes $v1.

We can categorize the system calls (syscalls) in MIPS assembly in 3 category:

  1. Print Syscalls: These syscalls are used to output data. They can print different types of data including integers, floating-point numbers, and strings. The data to be printed is typically passed in a specific register (like $a0 or $f12).

  2. Read Syscalls: These syscalls are used to read input data from the user. They can read different types of data including integers, floating-point numbers, and strings. The read data is typically returned in a specific register (like $v0 or $f0), or stored in a buffer whose address is passed in a specific register (like $a0).

  3. Exit Syscall: This syscall is used to terminate the program. It doesn’t require any arguments and doesn’t return any result.

Note

Remember, these are just some of the basic syscalls. MIPS provides many other syscalls for various purposes, such as file I/O, memory allocation, and process control.

Print syscalls are used to output data. They can print different types of data including integers, floating-point numbers, and strings. The data to be printed is typically passed in a specific register (like $a0 or $f12).

Print integer 

li $v0, 1
move $a0, $t0  # Assume $t0 contains the integer to print
syscall

Print float 

li $v0, 2
l.s $f12, float_value  # Assume float_value is a .float directive
syscall

Print string 

li $v0, 4
la $a0, string  # Assume string is a null-terminated string
syscall

Read Syscalls

Read syscalls are used to read input data from the user. They can read different types of data including integers, floating-point numbers, and strings. The read data is typically returned in a specific register (like $v0 or $f0), or stored in a buffer whose address is passed in a specific register (like $a0).

Read integer 

li $v0, 5
syscall
move $t0, $v0  # $t0 now contains the read integer

Read float 

li $v0, 6
syscall
mov.s $f12, $f0  # $f12 now contains the read float

Read string 

li $v0, 8
la $a0, buffer  # Assume buffer is a .space directive
li $a1, 100     # Read up to 100 characters
syscall

Exit Syscall

The exit syscall is used to terminate the program. It doesn’t require any arguments and doesn’t return any result.

Exit 

li $v0, 10
syscall

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