Kernel Dev In assembly & C -


i trying create simple kernel using assembly , c on linux using bochs. problem each time try calling c code assembly code emulator gives me error , resets simulation. when start in 16 bit real mode use code

global _start  [bits 16]  _start:  mov [boot_drive] , dl  mov bp , 0x7000 mov sp , bp  mov bx , 0x0000 ;load 5 sectors 0x0000(es):0x9000(bx) mov es , bx mov bx , kernel_offset mov dh , 15 mov dl , [boot_drive] call disk_load  mov dx , [es:kernel_offset] call print_hex  call switch_to_pm  jmp $

and after switching protected mode code

[bits 32] extern kmain  begin_pm:  ;print char vram testing , printed, means switch has suceeded mov ebx , vram_address mov al , 'h' mov [ebx] , al mov al , 0x07 inc ebx mov [ebx] , al  call kmain  jmp $

and c function nothing empty one

about commands using use these 

nasm $asm_file_name.asm -f elf -o $asm_file_name.o gcc -ffreestanding -c $c_file_name.c -o $c_file_name.o ld -o $c_file_name.bin -ttext 0x7c00 $asm_file_name.o $c_file_name.o --oformat binary dd status=noxfer conv=notrunc if=$c_file_name.bin of=$floppy_name.img

i don't problem. ideas ?

note: using following gdt , switch_to_pm functions

    ;gdt gdt_start:      gdt_null:         dd 0x0         dd 0x0      gdt_code: ;the code segment descriptor         ; base = 0x0 , limit = 0xfffff ,         ; 1 st flags : ( present )1 ( privilege )00 ( descriptor type )1 -> 1001 b         ; type flags : ( code )1 ( conforming )0 ( readable )1 ( accessed )0 -> 1010 b         ; 2 nd flags : ( granularity )1 (32 - bit default )1 (64 - bit seg )0 ( avl )0 -> 1100 b         dw 0xffff         ; limit (bits 0 -15)         dw 0x0         ; base (bits 0 -15)         db 0x0         ; base ( bits 16 -23)         db 10011010b ; 1st flags , type flags         db 11001111b ; 2nd flags , limit (bits 16 -19)         db 0x0         ; base ( bits 24 -31)      gdt_data: ; data segment descriptor         ; same code segment except type flags :         ; type flags : ( code )0 ( expand down )0 ( writable )1 ( accessed )0 -> 0010 b         dw 0xffff         ; limit ( bits 0 -15)         dw 0x0         ; base ( bits 0 -15)         db 0x0         ; base ( bits 16 -23)         db 10010010b ; 1 st flags , type flags         db 11001111b ; 2 nd flags , limit ( bits 16 -19)         db 0x0         ; base ( bits 24 -31)      gdt_end:     ; reason putting label @ end of     ; gdt can have assembler calculate     ; size of gdt gdt decriptor ( below )     ; gdt descriptior     gdt_descriptor:         dw gdt_end - gdt_start - 1         dd gdt_start      ; size of our gdt , less 1     ; of true size     ; start address of our gdt     ; define handy constants gdt segment descriptor offsets ,     ; segment registers must contain when in protected mode. example ,     ; when set ds = 0 x10 in pm , cpu knows mean use     ; segment described @ offset 0 x10 ( i.e. 16 bytes ) in our gdt , in our     ; case data segment (0 x0 -> null ; 0 x08 -> code ; 0 x10 -> data )     code_seg equ gdt_code - gdt_start     data_seg equ gdt_data - gdt_start [bits 16]  switch_to_pm:  cli lgdt[gdt_descriptor]  mov eax , cr0 or eax , 0x1 mov cr0 , eax  jmp code_seg:init_pm  [bits 32]  init_pm:  mov ax , data_seg mov ds , ax mov ss , ax mov es , ax mov fs , ax mov gs , ax  mov ebp , 0x9000 mov esp , ebp  jmp begin_pm

call kmain try find function @ address if whole code loaded @ 0x7c00. however, code in entirety loaded disk 0x9000. need ask linker fix address uses address kmain.

or better, @alexeyfrunze suggests, load code starting second sector place in memory directly after first sector loaded bios.


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