[Nasm-users] very strange behaviour indeed

[Martin K. <mar...@gm...>]

hi

i just came across some very strange behaviour of the nasm compiler
take a look at this piece of code:


   BITS 16

   ;some 16-Bit code

   cli
 
   lgdt [gdt_desc]

   mov eax, cr0   ;Enable

   or eax, 1   ;protected

   mov cr0, eax   ;mode

   jmp 20h:enter_32 ;where 20h is selector for this very segment




   BITS 32

enter_32:

   hlt    


if i execute this, the screen completely blanks upon the jump to enter_32

now if i leave out the line "BITS 32" (i.e. if i compile for 16 BITS), 
the screen stays as it is!

is there a sensible explanation for this??