## Copyright (C) 2021 Andrius Štikonas
## Copyright (C) 2023 Janneke Nieuwenhuizen <janneke@gnu.org>
## Copyright © 2023 Andrius Štikonas <andrius@stikonas.eu>
##
## 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/>.

:_start
	rd_fp rs1_sp mv        ; Protect stack pointer

	; Prepare argv
	rd_a0 rs1_fp !8 addi   ; ARGV_address = FP + 8
	rd_sp rs1_sp !-8 addi
	rs1_sp rs2_a0 sd       ; Put argv on the stack

	; Prepare envp
	rd_a0 rs1_fp mv        ; Address we need to load from
	rd_a0 rs1_a0 ld        ; Get ARGC
	rd_a0 rs1_a0 !2 addi   ; OFFSET = ARGC + 2
	rd_a0 rs1_a0 rs2_x3 slli ; OFFSET = OFFSET * WORDSIZE
	rd_a0 rs1_fp rs2_a0 add ; ENVP_address = RSP + OFFSET
	rd_sp rs1_sp !-8 addi
	rs1_sp rs2_a0 sd       ; Put envp on the stack

	; Stack offset
	rd_fp rs1_fp !8 addi

	; Init libc
	rd_ra $FUNCTION___init_io jal

	; Call main function
	rd_ra $FUNCTION_main jal

	; Put return value on the stack so that _exit gets it
	rd_sp rs1_sp !-16 addi
	rs1_sp rs2_a0 sd

	; Exit to kernel
	rd_a0 rs1_sp ld
	rd_a7 !93 addi         ; Syscall for exit
	ecall                  ; Exit with code in a0