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Dropping down to real mode for BIOS funcs

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This commit is contained in:
Thomas Oltmann 2026-02-18 00:39:02 +01:00
parent a6dd6b4328
commit 441d5ef570
2 changed files with 101 additions and 26 deletions
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17
Qcommon.c
View file

@ -27,12 +27,23 @@ void serial_write_char(char c)
outb(COM1_BASE_PORT, c);
}
void serial_write(const char *msg)
{
for (const char *c = msg; *c; c++) {
outb(0xE9, *c);
//serial_write_char(*c);
}
}
extern void writechar();
void
main()
{
outb(0xE9, 'X');
serial_write_char('X');
serial_write("init\r\n");
writechar();
serial_write("foo\r\n");
for (;;) {
__asm__ ("hlt" :);
//__asm__ ("hlt" :);
}
}

110
Rnbp.S
View file

@ -1,8 +1,6 @@
// vim: et:sw=12:ts=12:sts=12
.global _start
.text
.code16
.set SS_CODE16, 0x08
.set SS_DATA16, 0x10
@ -11,6 +9,57 @@
.macro PROT16
.code32
mov $SS_DATA16, %ax
mov %ax, %ds
mov %ax, %ss
ljmp $SS_CODE16, $9f
9: .code16
.endm
.macro PROT32
.code16
mov $SS_DATA32, %ax
mov %ax, %ds
mov %ax, %ss
ljmp $SS_CODE32, $9f
9: .code32
.endm
.macro REAL
mov %cr0, %eax
and $0xFFFE, %ax
mov %eax, %cr0
xor %ax, %ax
mov %ax, %ds
mov %ax, %es
mov real_ss, %ax
mov %ax, %ss
shl $4, %eax
sub %eax, %esp
ljmp $0x0000, $9f
9:
.endm
.macro PROT
mov %cr0, %eax
or $1, %eax
mov %eax, %cr0
xor %eax, %eax
mov $SS_DATA16, %ax
mov %ax, %ds
mov %ax, %es
mov %ax, %ss
mov real_ss, %ax
shl $4, %eax
add %eax, %esp
.endm
.text
.code16
// _start: entry point
_start: cli
cld
@ -19,10 +68,18 @@ _start: cli
mov %ax, %ds
mov %ax, %es
mov %ss, %ax
mov %ax, real_ss
push $msg_start
call dbgmsg
add $2, %sp
xor %bx, %bx
mov $0x0E, %ah
mov $'B', %al
int $0x10
// initialize our own BSS section
mov $_bss_start, %di
mov $_bss_end, %cx
@ -52,29 +109,10 @@ prot_enter:
lgdt GDT_PTR
// Set Protection Enable (PE) bit
mov %cr0, %eax
or $1, %al
mov %eax, %cr0
ljmp $SS_CODE32, $prot_trampo
PROT
PROT32
.code32
prot_trampo:
mov $SS_DATA32, %eax
mov %eax, %ds
mov %eax, %es
mov %eax, %fs
mov %eax, %gs
mov %eax, %ss
mov 'Y', %al
outb %al, $0xE9
// TODO load proper stack pointer
mov $0x90000, %ebp
mov %ebp, %esp
jmp main
.code16
@ -95,8 +133,34 @@ dbgmsg: push %bp
pop %bp
ret
.global writechar
.code32
writechar: push %ebp
mov %esp, %ebp
push %ebx
PROT16
.code16
REAL
xor %bx, %bx
mov $0x0E, %ah
mov $'A', %al
int $0x10
PROT
PROT32
.code32
pop %ebx
mov %ebp, %esp
pop %ebp
ret
.data
real_ss: .word 0
.global GDT
GDT: // entry 0: null descriptor