Challenge of handmade OS
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#include <Library/BaseLib.h>
#include <Library/MemoryAllocationLib.h>
#include <Library/PrintLib.h>
#include <Library/UefiLib.h>
#include <Uefi.h>
#include "io.h"
UINT64 SegmentDescriptors[] = {
0x0000000000000000, // NULL Descriptor
0x00AF9A000000FFFF, // BaseAddress 0 Granularity 1
// SegmentSize 1048575*4069=4294963200(4GB) Segment Present
// Plivilege 0 Code Segment Read+Exec
0x00CF93000000FFFF // BaseAddress 0 Granularity 1
// SegmentSize 1048575*4069=4294963200(4GB) Segment
// Present Plivilege 0 Data Segment Read+Write
};
IA32_DESCRIPTOR Descriptor;
void sendparallelstub(UINT8 byte) {
mapped_io_write(0x378, byte);
UINT8 control = mapped_io_read(0x37a);
mapped_io_write(0x37a, control | 1);
int a;
for (int i = 0; i < 200; i++) a += control;
mapped_io_write(0x37a, control);
}
void GDT_init() {
Descriptor.Limit = (UINT16)(sizeof(UINT64) * 3 - 1);
Descriptor.Base = (UINT32)(UINTN)(VOID *)SegmentDescriptors;
AsmWriteGdtr(&Descriptor);
asm volatile(
"mov $16, %ax\n"
"mov %ax, %ss\n"
"mov %ax, %ds\n"
"mov %ax, %es\n"
"mov %ax, %fs\n"
"mov %ax, %gs\n"
"sub $16,%rsp\n"
"leaq end(%rip),%rax\n"
"mov %rax,(%rsp)\n"
"mov $8,%ax\n"
"mov %ax,4(%rsp)\n"
"ljmp *(%rsp)\n"
"end:\n"
"add $16,%rsp");
}