Re: [PATCH 6/6] perf_counter: tools: Makefile tweaks for 64-bitpowerpc

From: Paul Mackerras
Date: Wed Jun 17 2009 - 08:28:33 EST

Ingo Molnar writes:

> ah, it does this:
> /*
> * This is here because we used to use l64 for 64bit powerpc
> * and we don't want to impact user mode with our change to ll64
> * in the kernel.
> */
> #if defined(__powerpc64__) && !defined(__KERNEL__)
> # include <asm-generic/int-l64.h>
> #else
> # include <asm-generic/int-ll64.h>
> #endif
> That's crappy really.

We were concerned that changing the userland-visible type of __u64
from unsigned long to unsigned long long, etc., would be breaking the
ABI, even if only in a small way - I thought it could possibly change
C++ mangled function names, for instance, and it would cause fresh
compile warnings on existing user code that prints __u64 with %lx,
which has always been the correct thing to do on ppc64.

A counter-argument would be, I guess, that __u64 et al. are purely for
use in describing the kernel/user interface, so we have a little more
latitude than with the type of e.g. u_int64_t. I dunno. I don't
recall getting much of an answer from the glibc guys about what they
thought of the idea of changing it.

Anyway, of the 64-bit architectures, alpha, ia64, and mips64 also have
__u64 as unsigned long in userspace, so this issue will still crop up
even if we change it on powerpc.

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