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 Post subject: Error when loading IDT in Long Mode
PostPosted: Wed Jul 21, 2021 11:23 am 
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Joined: Mon Aug 24, 2020 2:25 pm
Posts: 13
Hi everyone, I am developing a 64bit operating system. Right now I'm trying to create an Interrupt Descriptor Table (IDT), but I get an error that I can't get over. Someone can help me? Thanks!

The kernel.cpp:
Code:
#include "textPrint.cpp"
#include "idt.cpp"

extern "C" void _start(){
    setCursorPosition(positionFromCoords(0,0));
    InitializeIDT();
    return;
}


The idt.cpp:
Code:
#pragma once
#include "types.cpp"

/*Interrupt descriptor Table*/
struct IDT64{
   uint_16 offset_low;
   uint_16 selector;
   uint_8 ist;
   uint_8 types_attr;
   uint_16 offset_mid;
   uint_32 offset_high;
   uint_32 zero;
};
extern IDT64 _idt[256];
extern uint_64 isr1;
extern "C" void LoadIDT();

void InitializeIDT(){
   for (uint_64 t = 0; t < 256; t++){
      _idt[t].zero = 0;
      _idt[t].offset_low = (uint_16)(((uint_64)&isr1 & 0x000000000000ffff));
      _idt[t].offset_mid = (uint_16)(((uint_64)&isr1 & 0x00000000ffff0000) >> 16);
      _idt[t].offset_high = (uint_32)(((uint_64)&isr1 & 0xffffffff00000000) >> 32);
      _idt[t].ist = 0;
      _idt[t].selector = 0x08;
      _idt[t].types_attr = 0x8e;
   }   
   outb(0x21, 0xfd);
   outb(0xa1, 0xff);
   LoadIDT();
}

extern "C" void isr1_handler(){
   printString(HexToString(inb(0x60)));
   //uint_8 scanCode = inb(0x60);
   outb(0x20, 0x20);
   outb(0xa0, 0x20);
}


The idt.asm
Code:
[extern _idt]
idtDescriptor:
  dw 4095
  dq _idt

  %macro PUSHALL 0
     push rax
     push rcx
     push rdx
     push r8
     push r9
     push r10
     push r11
  %endmacro

  %macro POPALL 0
     pop r11
     pop r10
     pop r9
     pop r8
     pop rdx
     pop rcx
     pop rax
  %endmacro

[extern isr1_handler]
isr1:
  PUSHALL
  call isr1_handler
  POPALL
  iretq
  GLOBAL isr1

LoadIDT:
  lidt[idtDescriptor]
  sti
  ret
  GLOBAL LoadIDT


O erro acontece quando, no idt.asm, rodo a função lidt, se apagar esta linha o erro não acontece, mas a idt também não é ativada. A minha idt é inválida? Na consola de debug do Bochs (no ficheiro anexo) parace-me que o código salta para um "void":

Quote:
read() on floppy image returns 0


Por outro lado parece-me que a idt é de facto inválida:
Quote:
interrupt(long mode): gate descriptor is not valid sys seg


Attachment:
File comment: The Bochs Report
report.txt [38.72 KiB]
Downloaded 44 times


The Github Repo: https://github.com/Jmallone/os-dev/tree/main/pt12/Sector%201


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 Post subject: Re: Error when loading IDT in Long Mode
PostPosted: Wed Jul 21, 2021 4:54 pm 
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Member
Member

Joined: Mon Jul 05, 2021 6:57 pm
Posts: 27
In GDT.ASM:

Code:
gdt_codedesc:
   dw 0xFFFF    ; Limit
   dw 0x0000   ; Base(low)
   db 0x00      ; base(medium)
   db 10011010b; Flags
   db 11001111b; Flags + upper limit
   db 0x00      ; Base(high)


The "flags + upper limit" is wrong for a long mode code segment. bit 7 should be clear, bit 6 ("L") should be set. The correct value would be 10101111b.


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