0

As the title says, I'm trying to write a simple boot loader in assembly to help with my virtual machine monitor that I've tried to implement using the D programming language. Can anyone help me resolve the following error, nasm -f elf64 -o bootloader.o boot.asm boot.asm:28: error: instruction not supported in 64-bit mode?

jmp eax is the instruction on line 28.

Here is the assembly code:

section .text align=1
start:
    ; Load the kernel code into memory
    mov edx, 0x8000
    mov dh, 0x02
    mov dl, 0x80
    mov ah, 0x02
    int 0x13
    jnc kernel_loaded
    jmp error

kernel_loaded:
    ; Set the entry point for the kernel
    mov eax, [0x8000 + 0x218]
    mov ecx, [0x8000 + 0x21A]
    mov edx, 0
    add edx, ecx
    add ecx, ecx
    add edx, ecx
    add ecx, ecx
    add edx, ecx
    add ecx, ecx
    add edx, ecx
    add ecx, ecx
    add edx, ecx
    add eax, edx
    add eax, 0x8000
    jmp eax
    ; Display "Loading complete." on the screen
    mov ah, 0x00
    mov al, 'L'
    int 0x10
    mov ah, 0x00
    mov al, 'o'
    int 0x10
    mov ah, 0x00
    mov al, 'a'
    int 0x10
    mov ah, 0x00
    mov al, 'd'
    int 0x10
    mov ah, 0x00
    mov al, 'i'
    int 0x10
    mov ah, 0x00
    mov al, 'n'
    int 0x10
    mov ah, 0x00
    mov al, 'g'
    int 0x10
    mov ah, 0x00
    mov al, ' '
    int 0x10
    mov ah, 0x00
    mov al, 'c'
    int 0x10
    mov ah, 0x00
    mov al, 'o'
    int 0x10
    mov ah, 0x00
    mov al, 'm'
    int 0x10
    mov ah, 0x00
    mov al, 'p'
    int 0x10
    mov ah, 0x00
    mov al, 'l'
    int 0x10
    mov ah, 0x00
    mov al, 'e'
    int 0x10
    mov ah, 0x00
    mov al, 't'
    int 0x10
    mov ah, 0x00
    mov al, 'e'

error:
    ; Error handling code here

    ; Pad the boot loader to 512 bytes
    times 510 - ($-$$) db 0
    dd 0xAA55

I tried removing jmp eax from the assembly code but I feel like that might be a bad move. It did allow everything to get compiled and run in virtualbox but I see no output.

Here's how I built the iso file:

1) dmd -c vmmonitor.d
2) nasm -f elf64 -o bootloader.o boot.asm
3) ld -Ttext 0x7C00 -o boot.bin bootloader.o vmmonitor.o -L /usr/include/dmd/phobos/ -lphobos2
4) genisoimage -o boot.iso -b boot.bin -no-emul-boot boot.bin
Improve this question
4
  • 1
    dd 0xAA55 is the boot signature for a 16-bit legacy BIOS MBR bootloader. The firmware will have the CPU in 16-bit real mode when it jumps to this code at linear address 0x7C00, so you'd better be assembling for bits 16 mode, not 64-bit!! int 0x10 and int 0x13 calls only work in 16-bit mode. jmp eax should work, although you you might run into segment limits if it's outside 64K. Also, you want dw not dd there; dd would make a 514 byte file, with two zeros after the boot signature. Commented Feb 14, 2023 at 2:14
  • 1
    What's up with that sequence of add edx,ecx and then doubling ECX? Can't you get the same shift-and-add with imul edx, ecx, 0b11111111 or something? Maybe that's not the right constant. Also don't forget to set ds before using it implicitly via addressing modes like [0x8000 + 0x21A]; BIOSes might leave it set arbitrarily, not necessarily matching CS even. Related: Michael Petch's tips for bootloader development. Commented Feb 14, 2023 at 2:19
  • Also BTW, normally if using NASM, you'd use nasm -fbin to make a flat binary directly; org 0x7c00 would tell NASM to assume addresses start at 7C00 for the first byte of this section, like you're doing with ld -Ttext 0x7C00 when you assemble into an ELF object file and link. I guess if you want to link with another .o you could do it this way, but it's often easier to develop the "kernel" separately from the bootloader, not linking into one binary that loads the rest of itself. Commented Feb 14, 2023 at 2:22
  • Anyway, as for the error message in your question, look at the manual: felixcloutier.com/x86/jmp - the JMP r/m32 is "not supported" in 64-bit mode, the mode you're assembling for with nasm -f elf64 which you haven't overridden with bits 16. Commented Feb 14, 2023 at 2:25
Related questions
0
NA's appearing when subtracting one number from another in R
0
why sometimes R can't tell difference between NA and 0?
0
R: How to recode values of a variable to NA for cases where another variable has a value of NA
Load 7 more related questions Show fewer related questions

0

Reset to default

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.