Hans, On Fri, 9 Oct 2015, Hans Zuidam wrote: > On 9 okt. 2015, at 11:06, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > You cannot use an explicit 32bit read. We need an access which > > handles the fault gracefully. > > The reason for the explicit read suggestion is to avoid the > _builtin_constant_p() in __copy_from_user_nocheck(). The GCC manual > says that there may be situations where it returns 0 even though the > argument is a constant. That's insane at best. > Although none of the compiler/kernel combinations we have tried > showed this happening, we think it is probably better to be safe > than sorry. So we would need something like: futex_copy_from_user() which can be mapped to __copy_from_user_inatomic() first. Then go through all architectures and the asm-generic stuff and provide the specific variants which are guaranteed to use a 32bit access. I really prefer that we don't have to do that and the compiler people get their act together and fix that _builtin_constant_p() thingy. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html