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SubjectRe: Userspace compiler support of "long long"
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On Jun 28, 2007, at 08:08:03, Jakub Jelinek wrote:
> On Thu, Jun 28, 2007 at 07:53:51AM -0400, Kyle Moffett wrote:
>> Oh, ok, that makes it even easier to say this with certainty:
>> Changing the other 64-bit archs to use "long long" for their 64-
>> bit numbers will not cause additional warnings. I'm also almost
>> certain there are no architectures which use "long long" for 128-
>> bit integers. (Moreover, I can't find hardly anything which does
>> 128-bit integers at all).
>
> unsigned long and unsigned long long have the same size, precision
> and alignment on all LP64 arches, that's true. But they have
> different ranks and more importantly they mangle differently in C+
> +. So, whether some user exposed type uses unsigned long or
> unsigned long long is part of the ABI, whether that's size_t,
> uintptr_t, uint64_t, u_int64_t or any other type, you can't change
> it without breaking the ABI.

That sounds *extraordinarily* broken. Hopefully this would *not*
affect the type of a function which is passed a C "struct" containing
the "long long", right?

Hmm, I guess the question is: Do we support people directly passing
__u64 to C++ functions in userspace? I could understand, perhaps,
passing around structures defined in the kernel headers, but
certainly not the kernel-internal types. The only reason we even
export those is so we can have a private set of bit-size-defined
types with which to define kernel ABI structures.

Cheers,
Kyle Moffett

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