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create IDT in Assembly https://forum.osdev.org/viewtopic.php?f=13&t=39634 |
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Author: | growlnx [ Sun Jan 10, 2021 10:12 pm ] |
Post subject: | create IDT in Assembly |
Hello everybody! I know in C is more easy but i'm trying to implement the IDT in pure assembly for learning purposes. Code: %ifndef IDT %define IDT extern K_int_handler idt_start: %assign i 0 %rep 32 irq %+i: dw <ADDRESS OF ISR> & 0FFFFh dw DATA_SEG ; 0x08 db 0 db 08eh dw <ADDRESS OF ISR> & 0FFFF0000h) >> 16 %assign i i+1 %endrep times (255-31) resb 0 ; fill rest of idt idt_end: idtr: dw idt_end - idt_start - 1 dd idt_start %assign i 0 %rep 32 isr %+i: cli pusha call K_int_handler popa sti iret %assign i i+1 %endrep idt_setup: pusha cli lidt [idtr] sti popa ret %endif ; IDT I want put the address of isr* in "<ADDRESS OF ISR>", does anyone have any idea how to do? |
Author: | Octocontrabass [ Sun Jan 10, 2021 10:33 pm ] |
Post subject: | Re: create IDT in Assembly |
growlnx wrote: I want put the address of isr* in "<ADDRESS OF ISR>", does anyone have any idea how to do? If you're assembling a flat binary, you can perform arithmetic on labels. If you're assembling a proper object file to eventually link with other object files into a complete kernel binary, it's not possible. There are no x86 object file formats that support relocations for half of an address. |
Author: | growlnx [ Sun Jan 10, 2021 10:48 pm ] |
Post subject: | Re: create IDT in Assembly |
it will be a elf_i386 binary kernel to be loaded with GRUB. |
Author: | growlnx [ Sun Jan 10, 2021 10:53 pm ] |
Post subject: | Re: create IDT in Assembly |
Any ideas on how to get around this problem without resorting to high level? |
Author: | bzt [ Mon Jan 11, 2021 7:33 am ] |
Post subject: | Re: create IDT in Assembly |
growlnx wrote: Any ideas on how to get around this problem without resorting to high level? You can calculate the IDT entries in run-time instead of using macros. But I'd like to point out that it is very uncommon not to load the kernel at fixed address, therefore chances are good no relocation needed no matter the executable format (elf, pe, coff, aout etc.). In i386 elf (if it's not compiled as shared library) then the program headers tells the loader (GRUB) where to load the segments.Anyway, if you really want a relocatable kernel, then something like: Code: mov edi, idt_start Note these are not necessarily valid IDT operations, just examples. Do not copy'n'paste store_idt as-is.mov eax, label1 ; relocateable, as it has the entire label call store_idt mov eax, label2 call store_idt ; ... etc. ; --- store one IDT entry IN: edi=ptr to idt, eax=label OUT: edi=incremented --- store_idt: mov ebx, eax ; do the shifting and masking in run-time stosw ; store first part in IDT mov eax, 08e0008 stosd mov eax, ebx shr eax, 16 stosw ; store second part in IDT ret Cheers, bzt |
Author: | Octocontrabass [ Mon Jan 11, 2021 10:48 am ] |
Post subject: | Re: create IDT in Assembly |
growlnx wrote: Any ideas on how to get around this problem without resorting to high level? Everything you can do in a high-level language you can do in assembly. But if you're sure you'll never want to generate IDT entries at runtime, you can always rearrange the IDT entries. For example, exchange the ISR segment and the upper 16 bits of the ISR offset in your code (that way the ISR offset isn't split), then write some code that puts them back where they belong when your kernel boots. bzt wrote: But I'd like to point out that it is very uncommon not to load the kernel at fixed address, therefore chances are good no relocation needed no matter the executable format (elf, pe, coff, aout etc.). The linker still requires relocations in order to insert the correct fixed address at the correct location in the binary. |
Author: | bzt [ Mon Jan 11, 2021 11:25 am ] |
Post subject: | Re: create IDT in Assembly |
Octocontrabass wrote: The linker still requires relocations in order to insert the correct fixed address at the correct location in the binary. True, unless you use one compilation unit with an ORG directive. So it's safe to say you'll need run-time code, I guess? (I always do it in run-time anyway because I only install ISRs for which the drivers register an IRQ during boot)Cheers, bzt |
Author: | growlnx [ Tue Jan 12, 2021 10:56 am ] |
Post subject: | Re: create IDT in Assembly |
Well, then the easiest way to do this directly in the assembly is to imitate the result obtained in C. |
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