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Mathieu Maret bffe30c2a2 deal with shift keys 2 years ago
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Readme.md

Instruction

Build with make

Run with make test

Debug with qemu-system-x86_64 -boot a -fda mbr -s -S then gdb

 target remote localhost:1234
 layout asm
 b *0x7c00
 c

ASM reg

https://en.wikibooks.org/wiki/X86_Assembly/X86_Architecture

In 16 bits

There is 4 main 16bits reg: AX, BX, CX, DX. You can access the 8 MSB from AX with AH and the 8 LSB with AL.( BH,BL, CH, CL)

SI and DI are 16bits index register often used for pointer but can contains data.

SP is stack pointer, BP is base pointer

AX(AH, AL), BX(BH, BL), CX(CH, CL), DX(DH, DL), SI, DI, SP, BP

In 32bits

Main register are “Extended” to 32bits but 16bits of 8bits direct access is not possible anymore.

EAX, EBX, ECX, EDX, ESI, EDI, ESP, EBP

In 64bits

Prefixed by R RAX, RBX, RCX, RDX, RSI, RDI, RSP, RBP

Bios Memory

Address range Description
0x0 - 0x03FF IVT
0x400 - 0x4FF BIOS Data
0x500 - 0x7BFF Unused
0x7C00 - 0x7D77 Bootloader
0x7E00 - 0x9FFFF Unused
0xA0000 - 0xBFFFF Video memory
0xB0000 - 0xB7777 Video memory monochrome
0xB8000 - 0xBFFFF Video memory color
0xC0000 - 0xC7FFF BIOS ROM
0x80000 - 0xEFFFF BIOS shadow memory
0xF0000 - 0xFFFFF BIOS System

Interrupt Vector Table

INT_NUM Short Description PM
0x00 Division by zero
0x01 Debugger
0x02 NMI
0x03 Breakpoint
0x04 Overflow
0x05 Bounds
0x06 Invalid Opcode
0x07 Coprocessor not available
0x08 Double fault
0x09 Coprocessor Segment Overrun (386 or earlier only)
0x0A Invalid Task State Segment
0x0B Segment not present
0x0C Stack Fault
0x0D General protection fault
0x0E Page fault
0x0F reserved
0x10 Math Fault
0x11 Alignment Check
0x12 Machine Check
0x13 SIMD Floating-Point Exception
0x14 Virtualisation Exception
0x15 Control Protection Exception

BIOS IRQ

https://en.wikipedia.org/wiki/BIOS_interrupt_call