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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 14 Dec 2018 12:13:01 -0800
Message-ID: <CAHk-=wj0ejxYVV1xPfNX5YD6ZakRoSx+wQR==rFoj4J4SzLWhg@mail.gmail.com>
Subject: Re: Can we drop upstream Linux x32 support?
To:     Andy Lutomirski <luto@amacapital.net>
Cc:     dalias@libc.org, fweimer@redhat.com, bernd@petrovitsch.priv.at,
        glaubitz@physik.fu-berlin.de, Andrew Lutomirski <luto@kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        linux-api@vger.kernel.org, Peter Anvin <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>, bp@alien8.de,
        vapier@gentoo.org, hjl.tools@gmail.com, x32@buildd.debian.org,
        Arnd Bergmann <arnd@arndb.de>,
        Will Deacon <will.deacon@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>
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On Fri, Dec 14, 2018 at 10:58 AM Andy Lutomirski <luto@amacapital.net> wrot=
e:
>
> Does anyone know *why* Linux=E2=80=99s x32 has __kernel_long_t defined as=
 long long?

It *needs* to be long long, since the headers are used for builds in
user mode using ILP32.

Since __kernel_long_t is a 64-bit (the _kernel_ is not ILP32), you
need to use "long long" when building in ILP32.

Obviously, it could be something like

   #ifdef __KERNEL__
    typedef long __kernel_long_t;
   #else
    typedef long long __kernel_long_t;
   #endif

or similar to make it more obvious what's going on.

Or we could encourage all the uapi header files to always just use
explicit sizing like __u64, but some of the structures really end up
being "kernel long size" for sad historical reasons. Not lovely, but
there we are..

              Linus