Re: [PATCH 15/17] x86, mpx: do 32-bit-only cmpxchg for 32-bit apps

Borislav Petkov
2015-03-30T17:01:57Z

On Mon, Mar 30, 2015 at 09:57:14AM -0700, Dave Hansen wrote:
> > + if (is_64bit_mm(mm))
> > + return user_atomic_cmpxchg_inatomic(actual_old_val_ptr,
> > + bd_entry_addr,
> > + expected_old_val,
> > + new_bd_entry);
> > + else
> > + return futex_atomic_cmpxchg_inatomic((u32 *)actual_old_val_ptr,
> > + (u32 __user *)bd_entry_addr,
> > + expected_old_val,
> > + new_bd_entry);
> > }
>
> That does look tempting, and I appreciate the analysis.
>
> But, I'd really rather not hide this behind another layer of abstraction
> in order to save a few variable declarations. It's definitely _smaller_
> code, but it's a little less obvious what is going on.

If you rename futex_atomic_cmpxchg_inatomic to
atomic_cmpxchg_inatomic_32 or so, it is perfectly clear what's going on.

if (is_64bit_mm())
return user_atomic_cmpxchg_inatomic()
else /* 32-bit */
return user_atomic_cmpxchg_inatomic_32()

It can't get any more obvious than that.

:-D

--
Regards/Gruss,
Boris.

ECO tip #101: Trim your mails when you reply.
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