Helper macro and function for printenv.s and echo.s

helpers.s

  .section .text

# ************************************
# * print macro
# * Caller is responsible for setting
# * %ecx and %edx, and saving %eax and
# * %ebx if necessary.
# ************************************
.macro print
  movl $4, %eax
  movl $1, %ebx
  int $0x80
.endm

  .section .text

# ************************************
# * int strlen(char* str);
# * Returns the length of a string.
# ************************************
  .type strlen, @function
strlen:
  pushl %ebp
  movl  %esp, %ebp
  movl  $0, %eax           # Index
  movl  8(%ebp), %ecx      # Address of str
strlen_loop:
  movb  (%ecx,%eax,1), %dl # Current char
  cmpb  $0, %dl
  je    strlen_end
  incl  %eax
  jmp   strlen_loop
strlen_end:
  movl  %ebp, %esp
  popl  %ebp
  ret