On Wed, 2013-01-23 at 10:57 -0800, Sukadev Bhattiprolu wrote: > Michael Ellerman [mich...@ellerman.id.au] wrote: > | > | make: *** [tests/attr.o] Error 1 > | > | > | > | i386 compiles fine > | > > | > __u64 is 'unsigned long long' on x86 and PRIu64 is 'llu' which is fine. > | > > | > __u64 is 'unsigned long' on Power and PRIu64 is 'lu' which is again fine. > | > > | > But __u64 is 'unsigned long long' on x86_64, but PRIu64 is '%lu' bc > __WORDSIZE > | > is 64. > | > | > | This is a bit of a mess, but let me see if I can help explain it. > > Yes it is :-) thanks for explaining it. > > | > | The root of the problem is that you're mixing up the kernel type __u64, > | with the userspace format specifier PRIu64. > > struct perf_event_attr is shared with user space and is using __u64. Should > it use uint64_t instead ?
Absolutely not. That's the whole reason we have __u64, it's so we can define it in the kernel but share it with userspace, and not have it conflict with any userspace types. > | PRIu64 is the format specifier for printing a uint64_t, it _may_ also be > | the right specifier for a __u64, but there's no guarantee of that - as > | you have discovered. > | > | Inside the kernel both x86 and powerpc use unsigned long long always, in > | 32-bit and 64-bit code. That means in the kernel we can always use %llu. > | > | On x86 that definition is also exported to userspace, so on x86 __u64 is > | always unsigned long long. As you noticed this potentially differs from > | uint64_t, which can be confusing. However it means in x86 userspace code > | you can always print a __u64 with %llu. > | > | On powerpc we default to using definitions that match userspace, so > | __u64 changes depending on your wordsize, and so you must use PRIu64 > | etc. to print them. > > Well, using __u64 and PRIu64 seems breaks x86-64... Yes, see the previous paragraph. > | There is however support in recent powerpc kernels to switch to using > | unsigned long long even on 64-bit. See commit 2c9c6ce. > | > | You need to define __SANE_USERSPACE_TYPES__ before including types.h. > | Then you can always use %llu to print __u64. > > but __SANE_USERSPACE_TYPES__ with __u64 and %llu seems to work on x86, > x86-64, powerpc. > Will modify my patch to add __SANE_USERSPACE_TYPES__ but leave the %llu > as is. Right. It will only work with newer kernel headers, but that's basically unsolvable. cheers -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
