[solved] my OS get restarted when jmp to PM

[Tosi]

Because real mode segmentation works differently than protected mode segmentation. You loaded a GDT with a base of 0 and a limit of 4 GB which gives you a flat address space, and since you loaded to 0x0500 you have to explicitly jump to the address rather than an offset from it in protected mode.

[trinopoty]

It works because

Code: Select all

jmp 0x08:kernel32

compiles to 'jmp 0x08:0045' when 'org 0' which is incorrect.

When org 0x0500;

Code: Select all

jmp 0x08:kernel32

compiles to 'jmp 0x08:0x0545' which is correct.

[ym]

in my opinions,
org 0
means the variables 's address start from 0, and code offset from zero.
eg:
org 0
_start:
...
...
;offset 10
data01:

;_start should be 0, data01 should 10

org 0x7c00
means the variables 's address start from 0x7c00, and code offset from zero.
eg:
org 0x7c00
_start:
...
...
;offset 10
data01:

;_start should be 0, data01 should 0x7c10

bootsect load to 0:7c00 , if use org 0 data's addr start from 0, may read addr 0:10.
but the correct should read 0x7c10.

you can us ndisasm to disasmble your binary file , you can see the actual addr assigned.

[Combuster]

org 0x7c00
means the variables 's address start from 0x7c00, and code offset from zero.

Correction: code is also assembled to start at address 0x7c00. It makes an important difference when you use absolute jumps, like far jumps.