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

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Date:   Sun, 25 Apr 2021 15:16:54 -0400
From:   Zack Weinberg <zackw@...ix.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Alejandro Colomar <alx.manpages@...il.com>,
        bpf <bpf@...r.kernel.org>, linux-man <linux-man@...r.kernel.org>,
        "gcc-patches@....gnu.org" <gcc-patches@....gnu.org>,
        "libc-alpha@...rceware.org" <libc-alpha@...rceware.org>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] bpf.2: Use standard types and attributes

On Sat, Apr 24, 2021 at 4:43 PM David Laight via Libc-alpha
<libc-alpha@...rceware.org> wrote:
> From: Alexei Starovoitov
> > On Fri, Apr 23, 2021 at 4:15 PM Alejandro Colomar <alx.manpages@...il.com> wrote:
...
> > > Some pages also document attributes, using GNU syntax
> > > '__attribute__((xxx))'.  Update those to use the shorter and more
> > > portable C2x syntax, which hasn't been standardized yet, but is
> > > already implemented in GCC, and available through either --std=c2x
> > > or any of the --std=gnu... options.
..
> And the code below is no more portable that a #pragma'.
> It is probably worse than __attribute__((aligned(8)))
> +            uint64_t [[gnu::aligned(8)]] value;
> The standards committee are smoking dope again.
> At least the '__aligned_u64 value;' form stands a reasonable
> chance of being converted by cpp into whatever your compiler supports.

Is it actually necessary to mention the alignment overrides at all in
the manpages?  They are only relevant to people working at the level
of physical layout of the data in RAM, and those people are probably
going to have to consult the header file anyway.

zw