linux-kernel - Re: [RFC v2] bpf.2: Use standard types and attributes

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Message-ID: <87r1imgu5g.fsf@oldenburg.str.redhat.com>
Date:   Tue, 04 May 2021 21:45:31 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     "Alejandro Colomar (man-pages)" <alx.manpages@...il.com>
Cc:     Zack Weinberg <zackw@...ix.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        linux-man <linux-man@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        glibc <libc-alpha@...rceware.org>, GCC <gcc-patches@....gnu.org>,
        bpf <bpf@...r.kernel.org>,
        Joseph Myers <joseph@...esourcery.com>,
        David Laight <David.Laight@...lab.com>
Subject: Re: [RFC v2] bpf.2: Use standard types and attributes

* 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