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From:   Florian Weimer <fweimer@redhat.com>
To:     "Alejandro Colomar (man-pages)" <alx.manpages@gmail.com>
Cc:     Zack Weinberg <zackw@panix.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
        linux-man <linux-man@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        glibc <libc-alpha@sourceware.org>, GCC <gcc-patches@gcc.gnu.org>,
        bpf <bpf@vger.kernel.org>,
        Joseph Myers <joseph@codesourcery.com>,
        David Laight <David.Laight@aculab.com>
Subject: Re: [RFC v2] bpf.2: Use standard types and attributes
References: <20210423230609.13519-1-alx.manpages@gmail.com>
        <20210504110519.16097-1-alx.manpages@gmail.com>
        <CAADnVQLdW=jH1CUP02jokEu3Sh+=xKsCXvjA19kfz7KOn9mzkA@mail.gmail.com>
        <YJFZHW2afbAMVOmE@kroah.com>
        <69fb22e0-84bd-47fb-35b5-537a7d39c692@gmail.com>
        <YJFxArfp8wN3ILJb@kroah.com>
        <CAKCAbMg_eRCsD-HYmryL8XEuZcaM1Qdfp4XD85QKT6To+h3QcQ@mail.gmail.com>
        <6740a229-842e-b368-86eb-defc786b3658@gmail.com>
Date:   Tue, 04 May 2021 21:45:31 +0200
In-Reply-To: <6740a229-842e-b368-86eb-defc786b3658@gmail.com> (Alejandro
        Colomar's message of "Tue, 4 May 2021 20:54:07 +0200")
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* Alejandro Colomar:

> The thing is, in all of those threads, the only reasons to avoid
> <stdint.h> types in the kernel (at least, the only explicitly
> mentioned ones) are (a bit simplified, but this is the general idea of
> those threads):
>
> * Possibly breaking something in such a big automated change.
> * Namespace collision with userspace (the C standard allows defining
>   uint32_t for nefarious purposes as long as you don't include
>  <stdint.h>.   POSIX prohibits that, though)
> * Uglier

__u64 can't be formatted with %llu on all architectures.  That's not
true for uint64_t, where you have to use %lu on some architectures to
avoid compiler warnings (and technically undefined behavior).  There are
preprocessor macros to get the expected format specifiers, but they are
clunky.  I don't know if the problem applies to uint32_t.  It does
happen with size_t and ptrdiff_t on 32-bit targets (both vary between
int and long).

Thanks,
Florian