## 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/>.

## Exec_enable program
## Takes only single arg
## Shitty to use but essential if you need it

## ELF Header
7F 45 4C 46               ## e_ident[EI_MAG0-3] ELF's magic number
02                        ## e_ident[EI_CLASS] Indicating 64 bit
01                        ## e_ident[EI_DATA] Indicating little endianness
01                        ## e_ident[EI_VERSION] Indicating original elf
00                        ## e_ident[EI_OSABI] Set at 0 because none cares
00                        ## e_ident[EI_ABIVERSION] See above
00 00 00 00 00 00 00      ## e_ident[EI_PAD]
02 00                     ## e_type Indicating Executable
3E 00                     ## e_machine Indicating AMD64
01 00 00 00               ## e_version Indicating original elf
78 00 40 00 00 00 00 00   ## e_entry Address of the entry point
40 00 00 00 00 00 00 00   ## e_phoff Address of program header table
F0 01 00 00 00 00 00 00   ## e_shoff Address of section header table
00 00 00 00               ## e_flags
40 00                     ## e_ehsize Indicating our 64 Byte header
38 00                     ## e_phentsize size of a program header table
01 00                     ## e_phnum number of entries in program table
00 00                     ## e_shentsize size of a section header table
00 00                     ## e_shnum number of entries in section table
00 00                     ## e_shstrndx index of the section names

## Program Header
01 00 00 00               ## p_type
05 00 00 00               ## Flags
00 00 00 00 00 00 00 00   ## p_offset
00 00 40 00 00 00 00 00   ## p_vaddr
00 00 00 00 00 00 00 00   ## Undefined
B1 00 00 00 00 00 00 00   ## p_filesz
B1 00 00 00 00 00 00 00   ## p_memsz
00 00 20 00 00 00 00 00   ## Required alignment

## Start
	# first check that we got the correct number of inputs
	58                    ; pop %rax            # Get the number of arguments
	5f                    ; pop %rdi            # Get the program name
	5f                    ; pop %rdi            # Get the actual argument

	# Check if we have the correct number of inputs
	48 83 f8 02           ; cmp $2, %rax

	# Jump to Bail if the number is not correct
	75 20                 ; jne Bail

	# Load our preferred mode
	48 c7 c6 ed 01 00 00  ; mov $0755, %rsi

	# Load the syscall number for chmod
	48 c7 c0 5a 00 00 00  ; mov $90, %rax

	# Call the kernel
	0f 05                 ; syscall

## Done
	# program completed Successfully
	48 c7 c7 00 00 00 00  ; mov $0, %rdi        # All is well
	48 c7 c0 3c 00 00 00  ; mov $60, %rax       # put the exit syscall number in eax
	0f 05                 ; syscall             # Call it a good day

## Bail
	# Second terminate with an error
	48 c7 c7 01 00 00 00  ; mov $1, %rdi        # there was an error
	48 c7 c0 3c 00 00 00  ; mov $60, %rax       # put the exit syscall number in eax
	0f 05                 ; syscall             # bail out
