mini/elfloader/start.S
2009-05-15 15:09:04 +02:00

114 lines
2.2 KiB
ArmAsm

/*
mini - a Free Software replacement for the Nintendo/BroadOn IOS.
ELF loader: system startup
Copyright (C) 2008, 2009 Hector Martin "marcan" <marcan@marcansoft.com>
This program 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, version 2.
This program 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 this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
.arm
.extern _main
.extern __got_start
.extern __got_end
.extern __bss_start
.extern __bss_end
.extern __stack_addr
.extern delay
.globl _start
.globl debug_output
.section .init
_start:
@ Get real address of _start
sub r4, pc, #8
@ Subtract offset to get the address that we were loaded at
ldr r0, =_start
sub r4, r4, r0
@ Output 0x42 to the debug port
mov r0, #0x42
bl debug_output
@ Set up a stack
ldr sp, =__stack_addr
add sp, r4
@ Output 0x43 to the debug port
mov r0, #0x43
bl debug_output
@ relocate the GOT entries
ldr r1, =__got_start
add r1, r4
ldr r2, =__got_end
add r2, r4
got_loop:
@ check for the end
cmp r1, r2
beq done_got
@ read the GOT entry
ldr r3, [r1]
@ add our base address
add r3, r4
str r3, [r1]
@ move on
add r1, r1, #4
b got_loop
done_got:
@ clear BSS
ldr r1, =__bss_start
add r1, r4
ldr r2, =__bss_end
add r2, r4
mov r3, #0
bss_loop:
@ check for the end
cmp r1, r2
beq done_bss
@ clear the word and move on
str r3, [r1]
add r1, r1, #4
b bss_loop
done_bss:
mov r0, #0x44
bl debug_output
@ take the plunge
mov r0, r4
bl _main
@ _main returned! Go to whatever address it returned...
mov r1, r0
mov r0, r4
mov pc, r1
.pool
debug_output:
@ load address of port
mov r3, #0xd800000
@ load old value
ldr r2, [r3, #0xe0]
@ clear debug byte
bic r2, r2, #0xFF0000
@ insert new value
and r0, r0, #0xFF
orr r2, r2, r0, LSL #16
@ store back
str r2, [r3, #0xe0]
mov pc, lr