# pcboot - bootable PC demo/game kernel
-# Copyright (C) 2018 John Tsiombikas <nuclear@member.fsf.org>
+# Copyright (C) 2018-2019 John Tsiombikas <nuclear@member.fsf.org>
#
# 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
.extern wait_vsync
.extern kb_getkey
+ .equ STACKTOP,0x80000
+
# move the stack to the top of the conventional memory
cli
- movl $0x80000, %esp
+ movl $STACKTOP, %esp
+ # push a 0 ret-addr to terminate gdb backtraces
+ pushl $0
# zero the BSS section
xor %eax, %eax
hlt
jmp 0b
+ # this is called once after memory init, to move the protected mode
+ # stack to the top of usable memory, to avoid interference from 16bit
+ # programs (as much as possible)
+ .global move_stack
+move_stack:
+ # calculate the currently used lowest address of the stack (rounded
+ # down to 4-byte alignment), to see where to start copying
+ mov %esp, %esi
+ and $0xfffffffc, %esi
+ # calculate the size we need to copy
+ mov $STACKTOP, %ecx
+ sub %esi, %ecx
+ # load the destination address to edi
+ mov 4(%esp), %edi
+ sub %ecx, %edi
+ # size in longwords
+ shr $2, %ecx
+
+ # change esp to the new stack
+ mov $STACKTOP, %ecx
+ sub %esp, %ecx
+ mov 4(%esp), %eax
+ mov %eax, %esp
+ sub %ecx, %esp
+
+ rep movsd
+ ret
+
.global logohack
logohack:
pusha