stage0/Linux Bootstrap/read.s

93 lines
2.5 KiB
ArmAsm

## Copyright (C) 2016 Jeremiah Orians
## This file is part of stage0.
##
## stage0 is free software: you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## stage0 is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with stage0. If not, see <http://www.gnu.org/licenses/>.
.data
# we must export the entry point to the ELF linker or loader.
# They convientionally recognize _start as their entry point.
# Use ld -e main to override the default if you wish
.global _start
_start:
# first check that we got the correct number of inputs
pop %rax # Get the number of arguments
pop %rdi # Get the program name
pop %rdi # Get the actual argument
# Check if we have the correct number of inputs
cmp $2, %rax
# Jump to Bail if the number is not correct
jne Bail
# attempt to open the file for reading
mov $0, %rsi # prepare read_only
# we already have what we need in ebx
mov $2, %rax # the syscall number for open()
syscall # call the Kernel
# Check if we have a valid file
test %rax, %rax
# Jump to Bail_file if not actual file
js Bail
mov %rax, %rdi # move the pointer to the right location
Circle: #print contents of file
mov $read_size, %rdx # set the size of chars we want
mov $buffer, %rsi # Where to put it
# We already have what we need in ebx
mov $0, %rax # the syscall number for read
syscall # call the Kernel
test %rax, %rax # check what we got
jz Done # Got EOF call it done
# Make sure we don't write a bunch of NULLs
mov %rax, %rdx
# get file pointer out of the way
movq %rdi, %rsp
# edx was already setup
mov $1, %rdi # setup stdout write
mov $1, %rax # setup the write
syscall # call the Kernel
#now to prepare for next loop
movq %rsp, %rdi
jmp Circle
Done:
# program completed Successfully
mov $0, %rdi # All is well
mov $60, %rax # put the exit syscall number in eax
syscall # Call it a good day
Bail:
# terminate with an error
mov $1, %rdi # there was an error
mov $60, %rax # put the exit syscall number in eax
syscall # bail out
# Our writable space
# 2^ 30 Should be enough per read
read_size = 1073741824
buffer:
.space 1