assembly - How to setup Stack segment in protected mode? -


this problem defined 1 data , stack segment in x86 protected mode selector under gdt. when jmp protected mode, seems can access data section crash when push eax. see following code:

%include "../inc/descriptor.asm" %include "../inc/define.asm"  org     7c00h         jmp  begin ; ----------------------------------------------------------------------- ; const variable stack_base  equ  1000000h       ; 16m data_base   equ  2000000h       ; 32m stack_size  equ     8000h       ; 32k stack_limit equ  1008000h       ; 16m + 32k data_size   equ   100000h       ;  1m  ; gdt , ldt ; descriptor                  base               limit        property [section .gdt] gdt:        descriptor           0,                  0,              0 ldt_code32: descriptor           0, seg_code32_len - 1,   da_c + da_32 ldt_video:  descriptor     0b8000h,             0ffffh,         da_drw ldt_stack:  descriptor  stack_base,     stack_size - 1, da_drwa + da_b ldt_data:   descriptor   data_base,      data_size - 1,         da_drw  gdtlen equ $ - gdt gdtptr dw  gdtlen - 1        dd  0  ; selectors slt_code32 equ ldt_code32 - gdt slt_video  equ ldt_video - gdt slt_stack  equ ldt_stack - gdt slt_data   equ ldt_data - gdt ; -----------------------------------------------------------------------   ; real mode code [section .s16] [bits 16] begin:          mov     ax, cs          mov     ds, ax           ; init 32 bits code section descriptor          xor     eax, eax          mov     ax, cs          shl     eax, 4          add     eax, code32          mov     word [ldt_code32 + 2], ax          shr     eax, 16          mov     byte [ldt_code32 + 4], al          mov     byte [ldt_code32 + 7], ah           ; prepare loading gdtr          xor     eax, eax          mov     ax, ds          shl     eax, 4          add     eax, gdt          mov     dword [gdtptr + 2], eax           lgdt    [gdtptr]           cli           in      al, 92h          or      al, 10b          out     92h, al           mov     eax, cr0          or      eax, 1          mov     cr0, eax            jmp     dword slt_code32:0  ; protected mode code [section .s32] [bits 32] code32:          mov     ax, slt_video          mov     gs, ax           mov     ax, slt_stack          mov     ss, ax          mov     esp, stack_limit - 16          mov     ax, slt_data          mov     ds, ax          mov     eax, 012345678h          xor     edx, edx          mov     [edx], eax          mov     edx, [edx]          push    eax ;             **<= crashed here.**           ; ---------------------------------          ; prepare debug char          mov     ax, slt_video          mov     gs, ax          mov     bh, 0ch          mov     bl, 'b'          mov     esi, (80 * 1 + 1) * 2          mov     [gs:esi], bx          jmp     $          ; ; end of prepare debug char          ; ---------------------------------          push    eax           pop     ebx          mov     eax, data_base          mov     dword [eax], ebx           mov     edi, 0          mov     esi, (80 * 1 + 1) * 2          call    print_dword          jmp     $           ; ---------------------------------          ; ; prepare debug char          ; mov     ax, slt_video          ; mov     gs, ax          ; mov     bh, 0ch          ; mov     bl, 'b'          ; mov     esi, (80 * 1 + 1) * 2          ; mov     [gs:esi], bx          ; jmp     $          ; ; end of prepare debug char          ; ---------------------------------  seg_code32_len equ $ - code32 times    290 - ($ - $$) db 0 dw       0xaa55 ; command reference: ;     nasm protected_mode.asm -o pm.bin ;     dd if=pm.bin of=pm.img bs=512 count=1

descriptor.asm:

; ; descriptor base, limit, attr ;     base:  dd ;     limit: dd low 20 bits available ;     attr:  dw low nibble of higher byte 0 ; %macro descriptor 3        dw    %2 & 0ffffh        dw    %1 & 0ffffh        db    (%1 >> 16) & 0ffh        dw    ((%2 >> 8) & 0f00h) | (%3 & 0f0ffh)        db    (%1 >> 24) & 0ffh %endmacro ;

define.asm:

; da_32         equ 4000h da_drw        equ   92h da_drwa       equ   93h da_c          equ   98h da_b          equ da_32 da_element_4k equ 8000h ;  ; paging entry attribute pg_p    equ    1 pg_rw_w equ    2 pg_us_u equ    4

since set segment base stack_base must not add stack pointer. such, mov esp, stack_limit - 16 should mov esp, stack_size - 16.

ps: never set cs, code might break on systems it's not zero.


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