From: nowhere@nevernet.at   
      
   On 14/02/2022 16:55, James Harris wrote:   
      
   >> [about stack...]   
      
   > I have previously only ever had to think about Real Mode (which is   
   > always 16-bit) or the form of Protected Mode which is entirely 32-bit,   
   > i.e. where all segments are 32-bit. The idea of having PMode where some   
   > segments are 16-bit and others are 32-bit is entirely new to me but I   
   > think it is yielding insights into how the processor works.   
      
   I played a lot around with these options and finally decided for a mix.   
      
   [the Big bit...]>> you mean implicit stack references (all push pop call   
   return)?   
   > Yes.   
      
   > When working with a mix of 16-bit and 32-bit segments it seems there are   
   > at least THREE sizes we need to be aware of.   
   ...   
   > So where are such sizes defined?   
   ...   
   I knew all that :)  just didn't remember because there were no problems.   
      
   >> BUT how about   
   >> PM32:   
   >> 8B 44 24 fc     mov eax.[esp-04]  ;SP or ESP depending on seg-size ?   
   >> RM:   
   >> 67 8B 44 24 fc  mov ax,[esp-04]   ;could have an UnReal flat big stack   
      
   > How do you interpret those?   
      
   my disassembler do this for me.   
   >   
   > BTW, what happens when referring to BP or EBP as in   
   >   
   >    mov eax, [ebp + 4]   
   >    sub ebp, 8   
   >   
   > Does such code use the SS descriptor's B bit?   
      
   Yes, at least on CPUs which still support the B bit.   
   >> and I'm not sure yet if my mixed code CALL/RET work on SP only due to   
   >> my 16 bit stack. OK I use 66 c3 and 66 E8xxxxxxxx here and there and   
   >> my esp is always in 16 bit range (initially decided to fit BIOS calls).   
   >> So I never noticed it's using only SP.   
      
   > Does the above help?   
      
   :) thanks it helped to remember.   
   __   
   wolfgang   
      
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