sh.s

用于汇编领域的,运用于OS的MAIN函数.基于硬件基础的源代码

.globl _start
_start:
# infinite loop
# write(1, "$", 1): print out prompt
# 1st arg in ebx, 2nd arg in ecx, 3rd arg in edx  
   movl $1, %ebx   # fd=1, the standard output
   movl $prompt, %ecx  # put the addr of prompt in ecx
   movl $1, %edx   # n=1
   movl $4, %eax
   int $0x80
# n=read(0, buf, 20): read max 20 bytes from keyboard
   movl $0, %ebx
   movl $buf, %ecx # put the addr of buf iin ecx
   movl $20, %edx
   movl $3, %eax
   int $0x80
   # eax has the length. make it a string. hos already made it a string 
   # movl $0, buf(%eax) # put 0 in buf[eax]
#  fork()
   movl $2, %eax
   int $0x80
   cmpl $0, %eax
   je   child
parent:
   # wait()
   movl $7, %eax
   int $0x80
   jmp _start # go back to infinite loop
child:
   # exec(buf). exec to program in buf
   movl $buf, %ebx
   movl $11, %eax
   int $0x80

buf: .fill 20,1,0
prompt: .asciz "$"