ATT Assembly and Standard Input (stdin)

Introduction

In the world of assembly language programming, the AT&T syntax is widely used. It was developed by AT&T for use in Unix systems. Standard input (stdin) is a stream of data that comes from the keyboard or an input file. In this article, we'll explore the use of AT&T assembly with stdin.

Reading Input from stdin

To read input from standard input (stdin) using AT&T assembly, we first need to link our code with the C library. We can do this by using the GCC compiler with the -lc flag.

.section .bss
    .lcomm buffer, 1024
.section .data
    msg:
        .asciz "Enter a string: "
.section .text
    .globl _start
_start:
    movl $4, %eax       # syscall for write
    movl $1, %ebx       # file descriptor for stdout
    movl $msg, %ecx     # message to print
    movl $15, %edx      # length of message
    int $0x80           # call the kernel
    
    movl $3, %eax       # syscall for read
    movl $0, %ebx       # file descriptor for stdin
    leal buffer, %ecx   # address of buffer
    movl $1024, %edx    # maximum number of bytes to read
    int $0x80           # call the kernel
    
    movl $4, %eax       # syscall for write
    movl $1, %ebx       # file descriptor for stdout
    movl $buffer, %ecx  # string to print
    int $0x80           # call the kernel
    
    movl $1, %eax       # syscall for exit
    movl $0, %ebx       # exit code
    int $0x80           # call the kernel

In this example, we first define a buffer for storing the input from stdin. We then define a message to print, asking for input. We then use the write syscall to output the message to stdout. We then use the read syscall to read input from stdin into the buffer. Finally, we use the write syscall again to output the input from the buffer to stdout.

Conclusion

In this article, we've explored the use of AT&T assembly language programming with standard input (stdin). We've seen how to link our code with the C library, and how to use the read and write syscalls to interact with stdin and stdout. This knowledge should give you the tools you need to start working on your own assembly language projects that utilize standard input.