Re: [Qemu-devel] [PATCH] Bug in AMD64 emulation Was: [AMD64] Possible problem with the DF flag during the SYSCALL instruction

[Alexander Graf]

Hi,

On Mar 25, 2008, at 8:45 PM, Jakub Jermar wrote:

> as no one has picked my previous report up yet, I am resending my  
> patch again.  The patch fixes a bug in the way QEMU emulates AMD64  
> instruction called SYSCALL.  The problem appears to be stale DF  
> variable.

Sorry I didn't have a look at it before. Good catch though!

> Jakub
>
> --- helper.c    2008-01-06 20:38:45.000000000 +0100
> +++ helper.c.new        2008-03-20 22:39:17.000000000 +0100
> @@ -1008,6 +1008,7 @@
>                                DESC_S_MASK |
>                                DESC_W_MASK | DESC_A_MASK);
>         env->eflags &= ~env->fmask;
> +       DF = 1 - (2 * ((env->eflags >> 10) & 1));

I believe you're searching for load_eflags(), which automatically  
updates the DF flag. Take a look at the SVM code for that issue as  
well (helper.c:helper_vmrun).

>         if (code64)
>             env->eip = env->lstar;
>         else

Alex