2017-01-28 23:44:16 +01:00
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# Instruction
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2017-01-28 22:46:50 +01:00
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Build with
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2017-01-28 23:44:16 +01:00
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`nasm -f bin mbr.asm -o mbr`
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2017-01-28 22:46:50 +01:00
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Run with
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`qemu-system-x86_64 -boot a -fda mbr`
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2017-01-28 22:46:50 +01:00
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2017-01-28 23:31:26 +01:00
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Debug with
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2017-01-28 23:44:16 +01:00
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`qemu-system-x86_64 -boot a -fda mbr -s -S`
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then
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`gdb`
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```
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2017-01-28 23:31:26 +01:00
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target remote localhost:1234
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layout asm
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b *0x7c00
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c
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2017-01-28 23:44:16 +01:00
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```
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2017-01-28 23:31:26 +01:00
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2017-01-28 23:44:16 +01:00
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# ASM reg
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2017-01-28 23:40:54 +01:00
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2017-01-28 23:44:16 +01:00
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## In 16 bits
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There is 4 main 16bits reg: AX, BX, CX, DX.
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You can access the 8 MSB from AX with AH and the 8 LSB with AL.( BH,BL, CH, CL)
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SI and DI are 16bits index register often used for pointer but can contains data.
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SP is stack pointer, BP is base pointer
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AX(AH, AL), BX(BH, BL), CX(CH, CL), DX(DH, DL), SI, DI, SP, BP
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2017-01-28 23:44:16 +01:00
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## In 32bits
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Main register are "Extended" to 32bits but 16bits of 8bits direct access is not possible anymore.
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EAX, EBX, ECX, EDX, ESI, EDI, ESP, EBP
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## In 64bits
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Prefixed by R
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RAX, RBX, RCX, RDX, RSI, RDI, RSP, RBP
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2017-01-28 23:44:16 +01:00
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# Bios Memory
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Address range | Description
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----------------------- | -----------------------
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0x0 - 0x03FF |IVT
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0x400 - 0x4FF |BIOS Data
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0x500 - 0x7BFF |Unused
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0x7C00 - 0x7D77 |Bootloader
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0x7E00 - 0x9FFFF |Unused
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0xA0000 - 0xBFFFF |Video memory
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0xB0000 - 0xB7777 |Video memory monochrome
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0xB8000 - 0xBFFFF |Video memory color
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0xC0000 - 0xC7FFF |BIOS ROM
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0x80000 - 0xEFFFF |BIOS shadow memory
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0xF0000 - 0xFFFFF |BIOS System
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2017-01-28 23:44:16 +01:00
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# Interrupt Vector Table
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INT_NUM | Short Description PM
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----------- | ----------------------
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0x00 | Division by zero
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0x01 | Debugger
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0x02 | NMI
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0x03 | Breakpoint
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0x04 | Overflow
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0x05 | Bounds
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0x06 | Invalid Opcode
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0x07 | Coprocessor not available
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0x08 | Double fault
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0x09 | Coprocessor Segment Overrun (386 or earlier only)
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0x0A | Invalid Task State Segment
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0x0B | Segment not present
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0x0C | Stack Fault
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0x0D | General protection fault
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0x0E | Page fault
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0x0F | reserved
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0x10 | Math Fault
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0x11 | Alignment Check
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0x12 | Machine Check
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0x13 | SIMD Floating-Point Exception
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0x14 | Virtualisation Exception
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0x15 | Control Protection Exception
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2017-01-28 23:44:16 +01:00
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# BIOS IRQ
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2017-01-28 22:58:59 +01:00
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https://en.wikipedia.org/wiki/BIOS_interrupt_call
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