New crt0.s for ps2sdk
Posted: Fri Jul 13, 2007 9:32 am
I started looking at updating some of the ps2sdk and increasing general code quality. I started with updating the newlib-patch from 1.10.0 to 1.15.0 (still testing it, wait a few days) and also updating the custom ps2 code in there... While doing that I noticed that the crt0.s in there really, really sucks, and the one in ps2sdk isn't that pretty either, so I spent a few hours today rewriting it.
Changes
Updates 13/07
Changes
- Properly made _ps2sdk_* symbols weak (as they are in the SDK) so that it does no longer actually require PS2SDK to link properly.
- Return value is now stored before _fini() and _ps2sdk_libc_deinit() is called. It would otherwise have been overwritten by any function returning a value (or whenever the register was used inside a function).
- zerobss code is now better at handling edge cases
- A lot more readable than the previous version and should be easy to tweak for different uses.
- _exit() is now actually returning the proper returncode
Updates 13/07
- Dropped byte-range clearing of bss (it should be 128-bit aligned both in position and size)
Code: Select all
# _____ ___ ____ ___ ____
# ____| | ____| | | |____|
# | ___| |____ ___| ____| | \ PS2DEV Open Source Project.
#-----------------------------------------------------------------------
# Copyright (c) 2001-2007 ps2dev - http://www.ps2dev.org
# Licenced under Academic Free License version 2.0
# Review ps2sdk README & LICENSE files for further details.
#
# $Id:$
# Standard startup file.
.globl _init
.type _init, @function
.weak _init
.globl _fini
.type _fini, @function
.weak _fini
.extern _heap_size
.extern _stack
.extern _stack_size
.globl _ps2sdk_args_parse
.type _ps2sdk_args_parse, @function
.weak _ps2sdk_args_parse
.globl _ps2sdk_libc_init
.type _ps2sdk_libc_init, @function
.weak _ps2sdk_libc_init
.globl _ps2sdk_libc_deinit
.type _ps2sdk_libc_deinit, @function
.weak _ps2sdk_libc_deinit
.set noat
.set noreorder
.text
.align 2
nop
nop
.globl _start
.ent _start
_start:
zerobss:
# clear bss area
la $2, _fbss
la $3, _end
1:
sltu $1, $2, $3
beq $1, $0, 2f
nop
sq $0, ($2)
addiu $2, $2, 16
j 1b
nop
2:
# store eventual loader arguments (passed via a0)
la $2, _loader_args
sw $4, ($2)
setupthread:
# setup current thread
la $4, _gp
la $5, _stack
la $6, _stack_size
la $7, _args
la $8, _root
move $gp, $4
addiu $3, $0, 60
syscall # SetupThread(_gp, _stack, _stack_size, _args, _root)
move $sp, $2
# initialize heap
la $4, _end
la $5, _heap_size
addiu $3, $0, 61
syscall # SetupHeap(_end, _heap_size)
# writeback data cache
move $4, $0
addiu $3, $0, 100
syscall # FlushCache(0)
parseargs:
# call ps2sdk argument parsing (weak)
la $8, _ps2sdk_args_parse
beqz $8, 1f
nop
jal _getargs
nop
jalr $8 # _ps2sdk_args_parse(argc, argv)
nop
1:
libc_init:
# initialize ps2sdk libc (weak)
la $8, _ps2sdk_libc_init
beqz $8, 1f
nop
jalr $8 # _ps2sdk_libc_init()
nop
1:
ctors:
# call global constructors (weak)
la $8, _init
beqz $8, 1f
nop
jalr $8 # _init()
nop
1:
# call main
ei
jal _getargs
nop
jal main # main(argc, argv)
nop
# call _exit
j _exit # _exit(retval)
move $4, $2
.end _start
.align 3
.globl _exit
.ent _exit
.text
_exit:
la $2, _retval
sw $4, ($2)
dtors:
# call global destructors (weak)
la $8, _fini
beqz $8, 1f
nop
jalr $8 # _fini()
nop
1:
libc_uninit:
# uninitialize ps2sdk libc (weak)
la $8, _ps2sdk_libc_deinit
beqz $8, 1f
nop
jalr $8 # _ps2sdk_libc_deinit()
nop
1:
# conditional exit (depending on if we got arguments through the loader or not)
la $2, _retval
lw $4, ($2)
la $5, _loader_args
lw $6, ($5)
beqz $6, 1f
nop
# called from a loader, close thread
lw $7, ($6)
sw $0, ($7) # clear thread id
addiu $3, $0, 36
syscall # ExitDeleteThread() (noreturn)
1:
# not called from a loader, return to browser
addiu $3, $0, 4
syscall # Exit(retval) (noreturn)
.end _exit
.ent _root
_root:
addiu $3, $0, 35
syscall # ExitThread() (noreturn)
.end _root
.ent _getargs
_getargs:
# check normal arguments
la $2, _args
lw $3, ($2)
bnez $3, 1f
nop
# check for arguments passed by a loader
la $2, _loader_args
lw $3, ($2)
beqzl $3, 2f
addu $4, $0, 0
addiu $2, $3, 4
1:
lw $4, ($2)
addiu $5, $2, 4
2:
jr $ra # $4 = argc, $5 = argv
nop
.end _getargs
.bss
.align 6
_args:
.space 4+16*4+256 # argc, 16 arguments, 256 bytes payload
_loader_args:
.space 4 # pointer to loader arguments: thread id, argc, argv
_retval:
.space 4