Re: [PATCH 1/3] arch/x86: Use offsetof

["H. Peter Anvin" <hpa@zytor.com>]

Jan Engelhardt wrote:
> On Dec 26 2007 17:01, H. Peter Anvin wrote:
> > > > @@ -215,7 +215,9 @@ asmlinkage int sys_vm86old(struct pt_reg
> > > >   ret = -EFAULT;
> > > >   if (tmp)
> > > > 		goto out;
> > > > -	memset(&info.vm86plus, 0, (int)&info.regs32 - (int)&info.vm86plus);
> > > > +	memset(&info.vm86plus, 0,
> > > > +	       offsetof(struct kernel_vm86_struct, regs32) -
> > > > +	       offsetof(struct kernel_vm86_struct, vm86plus));
> > > I do not think this makes it more readable... (int) -> (char *) would
> > > make it portable and readable, AFAICT.
> > >         Pavel
> > The right way to do it is:
> >
> > 	memset(&info.vm86plus, 0, sizeof info.vm86plus);
>
> Either way, downcasting a pointer to (int) is dangerous,
> even if this one occurrence happens to be in 32-bit-only code.

Actually, it would be safe (although stupid) in this case since the 
difference would still be 32 bits or less.

Doesn't make it any less wrong.

	-hpa
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