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[Bug 1902267] Re: CPU not support 32-bit stack in 32-bit unreal mode


From: Launchpad Bug Tracker
Subject: [Bug 1902267] Re: CPU not support 32-bit stack in 32-bit unreal mode
Date: Fri, 09 Jul 2021 04:17:20 -0000

[Expired for QEMU because there has been no activity for 60 days.]

** Changed in: qemu
       Status: Incomplete => Expired

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https://bugs.launchpad.net/bugs/1902267

Title:
  CPU not support 32-bit stack in 32-bit unreal mode

Status in QEMU:
  Expired

Bug description:
  QEMU version 5.0.0 supports 32-bit and 16-bit unreal mode. Great!
  Unfortunately, QEMU does not support 32-bit stack in unreal 32-bit mode.
  After the INT instruction, the stack is switched to 16-bit, which should not 
be the case. 
  At BOCHS, my code works 100%. At QEMU not works.

  Sample code to find out:

  use32
  cli
  mov ax,cs
  shl eax,16
  mov ax,NewInt80h
  mov [IDT32+4*80h],eax
  mov edx,esp
  mov esp,0x10000
  int 80h
  NewInt80h:
  xchg esp,edx
  cmp edx,0x10000-6
  jnz IsStack16Bit

  Stack selector loaded from GDT:
  GDT:
  real32_GDT            
  dq 0
  dw 0xFFFF,0x0000,9A00h,0xCF     ; 32-bit code descriptor
  dw 0xFFFF,0x0000,9200h,0x8F     ;   4 GB data descriptor
  dw 0xFFFF,0x0000,9A00h,0x00     ; 16-bit code descriptor
  dw 0xFFFF,0x0000,9200h,0xCF     ; 32-bit data descriptor stack

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