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

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Date:   Tue, 4 May 2021 07:12:01 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Alejandro Colomar <alx.manpages@...il.com>
Cc:     "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>,
        David Laight <David.Laight@...lab.com>,
        Zack Weinberg <zackw@...ix.com>,
        Joseph Myers <joseph@...esourcery.com>
Subject: Re: [RFC v2] bpf.2: Use standard types and attributes

On Tue, May 4, 2021 at 4:05 AM Alejandro Colomar <alx.manpages@...il.com> wrote:
>
> Some manual pages are already using C99 syntax for integral
> types 'uint32_t', but some aren't.  There are some using kernel
> syntax '__u32'.  Fix those.
>
> Some pages also document attributes, using GNU syntax
> '__attribute__((xxx))'.  Update those to use the shorter and more
> portable C11 keywords such as 'alignas()' when possible, and C2x
> syntax '[[gnu::xxx]]' elsewhere, 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.
>
> The standard isn't very clear on how to use alignas() or
> [[]]-style attributes, so the following link is useful in the case
> of 'alignas()' and '[[gnu::aligned()]]':
> <https://stackoverflow.com/q/67271825/6872717>
>
> Signed-off-by: Alejandro Colomar <alx.manpages@...il.com>
> Cc: LKML <linux-kernel@...r.kernel.org>
> Cc: glibc <libc-alpha@...rceware.org>
> Cc: GCC <gcc-patches@....gnu.org>
> Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>
> Cc: bpf <bpf@...r.kernel.org>
> Cc: David Laight <David.Laight@...LAB.COM>
> Cc: Zack Weinberg <zackw@...ix.com>
> Cc: Joseph Myers <joseph@...esourcery.com>
> ---
>  man2/bpf.2 | 49 ++++++++++++++++++++++++-------------------------
>  1 file changed, 24 insertions(+), 25 deletions(-)
>
> diff --git a/man2/bpf.2 b/man2/bpf.2
> index 6e1ffa198..04b8fbcef 100644
> --- a/man2/bpf.2
> +++ b/man2/bpf.2
> @@ -186,41 +186,40 @@ commands:
>  .PP
>  .in +4n
>  .EX
> -union bpf_attr {
> +union [[gnu::aligned(8)]] bpf_attr {
>      struct {    /* Used by BPF_MAP_CREATE */
> -        __u32         map_type;
> -        __u32         key_size;    /* size of key in bytes */
> -        __u32         value_size;  /* size of value in bytes */
> -        __u32         max_entries; /* maximum number of entries
> -                                      in a map */
> +        uint32_t    map_type;
> +        uint32_t    key_size;    /* size of key in bytes */
> +        uint32_t    value_size;  /* size of value in bytes */
> +        uint32_t    max_entries; /* maximum number of entries
> +                                    in a map */

For the same reasons as explained earlier:
Nacked-by: Alexei Starovoitov <ast@...nel.org>