Re: [Qemu-devel] restoring eflags after iret on x86

[malc]

On Sun, 7 Sep 2008, Cohn, Robert S wrote:

> I am working with 0.9.1 sources and have seen a problem with restoring
> eflags during an iret.
>
> helper_ret_protected Does this:
>    if (is_iret) {
>        /* NOTE: 'cpl' is the _old_ CPL */
>        eflags_mask = TF_MASK | AC_MASK | ID_MASK | RF_MASK | NT_MASK;
>        if (cpl == 0)
>            eflags_mask |= IOPL_MASK;
>        iopl = (env->eflags >> IOPL_SHIFT) & 3;
>        if (cpl <= iopl)
>            eflags_mask |= IF_MASK;
>        if (shift == 0)
>            eflags_mask &= 0xffff;
>        load_eflags(new_eflags, eflags_mask);
>  }
>
> My understanding is that it also needs to do:
> env->cc_op = CC_OP_EFLAGS
>
> Or else it will continue to use the old value of cc_op, which will not
> be consistent with the value that was just stored into cc_src.
>
> I looked at the trunk on svn and it appears to have the same problem. It
> is strange that iret is broken in this way and no one else is seeing the
> problem. Am I missing something?

Yes you do. Look at target-i386/translate.c after emiting the tcg
helper call to iret helper it sets s->cc_op to CC_OP_EFLAGS and
calls gen_eob which propgates this to env cc_op.

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