On Sunday 19 August 2007, Al Viro wrote: > On Sun, Aug 19, 2007 at 08:26:24PM -0700, David Brownell wrote: > > > ISTR the warning was the other way around: about "cast from integer > > to pointer of a different size". The __u64 came from userspace and > > the kernel pointer was only 32 bits. Not really truncation, but GCC > > could not know that directly ... ergo the extra non-pointer cast. > > And? Cast to integer type with the size equal to that of pointer. > unsigned long is just that on all supported targets.
Some tool kept warning about that. Presumably then-current sparse. I've certainly heard the conventional "unsigned long fits pointers" wisdom, but tools disagreed. (Does ANSI C guarantee that? I'd think not, or uintptr_t would not be needed.) And ptrdiff_t was the closest relevant data type that passed both gcc and sparse, since uintptr_t didn't previously exist everywhere. > More interesting question is whether you want an error returned when > pointers are 32bit and value doesn't fit into that... Either access_ok() or copy_from_user() reports an error if the pointer part of that u64 (N LSBs) is bad. As a general policy, I think the other part is undefined and irrelevant to the kernel ... it's a kind of explicit padding, and padding isn't valdated. (At most it's zeroed to prevent a covert channel, but that's not relevent here.) - Dave - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
