[Qemu-devel] Windows NT4 regression due to 0b57e287 ("cpu_physical_memory_write_rom() needs to do TB invalidates")

["Hervé Poussineau" <hpoussin@reactos.org>]

This commit breaks Windows NT4 boot.
QEMU crashes when NT4 switches from 80x25 to 80x43 resolution.

First bad commit is:

commit 0b57e287138728f72d88b06e69b970c5d745c44a
Author: David Gibson <david@gibson.dropbear.id.au>
Date:   Mon Sep 10 12:30:57 2012 +1000

    cpu_physical_memory_write_rom() needs to do TB invalidates
    
    cpu_physical_memory_write_rom(), despite the name, can also be used to
    write images into RAM - and will often be used that way if the machine
    uses load_image_targphys() into RAM addresses.
    
    However, cpu_physical_memory_write_rom(), unlike 
cpu_physical_memory_rw()
    doesn't invalidate any cached TBs which might be affected by the region
    written.
    
    This was breaking reset (under full emu) on the pseries machine - we 
loaded
    our firmware image into RAM, and while executing it rewrite the code at
    the entry point (correctly causing a TB invalidate/refresh).  When we
    reset the firmware image was reloaded, but the TB from the rewrite was
    still active and caused us to get an illegal instruction trap.
    
    This patch fixes the bug by duplicating the tb invalidate code from
    cpu_physical_memory_rw() in cpu_physical_memory_write_rom().
    
    Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
    Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>


gdb gives:
Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xb3584b70 (LWP 22345)]
#0  0x80276a36 in helper_stl_mmu (env=0x80bf9f48, addr=4294836352, 
val=0, mmu_idx=-2134925496)
    at softmmu_template.h:254
254        tlb_addr = env->tlb_table[mmu_idx][index].add_write
(gdb) bt
#0  0x80276a36 in helper_stl_mmu (env=0x80bf9f48, addr=4294836352, 
val=0, mmu_idx=-2134925496)
    at softmmu_template.h:254
#1  0xb537aa9e in code_gen_buffer ()
#2  0x0005849 in ?? ()
#3  0x80af3ce0 in ?? ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)
(gdb) p env
$1 = (struct CPUX86State *) 0x80bf9f48
(gdb) p index
$2 = 224

Command line is
qemu-system-i386 -cpu pentium -hda nt40.qcow2
KVM is not used.

Reverting the commit (and fixing the conflict) lets Windows NT4 work again.

Regards,

Hervé