Re: [Qemu-devel] Page protection and i386 cmpxchg8b

[Ilya Shar]

--- Pierre d'Herbemont <address@hidden> wrote:

> ...
> cvs diff -u would be easier to read for me. (or diff
> -u). You could  
> send this patch to the qemu-devel, that would be
> cool.
> 

Pierre, 

Please see the diff file attached. 

> ...
> Ouch! I have noticed the same: qemu can trigger bugs
> really easily at  
> the kernel level :( Could you explain how you know
> that cmpxchg8b is  
> the key to our problem? 

Stepping in gdb I saw that cmpxchg8b attempts to write
to a protected page.  Besides, when the system
crashes, here's what I see in the crash log in the
Console app:

...
Exception:  EXC_BAD_ACCESS (0x0001)
Codes:      KERN_PROTECTION_FAILURE (0x0002) at
0x2111faf5

Thread 0 Crashed:
0   qemu-i386   0x0e02254b stq_le_p + 50
(cpu-all.h:344)
1   qemu-i386   0x0e0224d6 helper_cmpxchg8b + 192
(helper.c:1523)
2   <<00000000>>        0x0e1361b4 code_gen_buffer +
708980
3   qemu-i386   0x0e000db3 cpu_loop + 23 (main.c:498)
4   qemu-i386   0x0e001f75 main + 2814 (main.c:917)
5   qemu-i386   0x0e000a8e _start + 216
6   qemu-i386   0x0e0009b5 start + 41

...

Any suggestions how to fix this?  

Thanks for your help! 
Ilya 

> Also qemu signal handlers
> might be overridden  
> by some mach calls, that could explain the problem
> you are  
> encountering. We need to work on this.
> 
> Pierre.
> 


 
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darwin-user_syscall.c_diff
Description: 2740739241-darwin-user_syscall.c_diff