netdev - Re: [PATCH bpf] libbpf: Fix libbpf hashmap on (I)LP32 architectures

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Message-ID: <CAEf4Bzbq9KPyn7RaRfowny=uOynuEM6ki5V+BuHR-tDDN1W_ew@mail.gmail.com>
Date:   Thu, 9 Jul 2020 15:59:13 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Bogusz <qboosh@...-linux.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf] libbpf: Fix libbpf hashmap on (I)LP32 architectures

On Thu, Jul 9, 2020 at 3:57 PM Andrii Nakryiko <andriin@...com> wrote:
>
> From: Jakub Bogusz <qboosh@...-linux.org>
>
> On ILP32, 64-bit result was shifted by value calculated for 32-bit long type
> and returned value was much outside hashmap capacity.
> As advised by Andrii Nakryiko, this patch uses different hashing variant for
> architectures with size_t shorter than long long.
>
> Fixes: e3b924224028 ("libbpf: add resizable non-thread safe internal hashmap")
> Signed-off-by: Jakub Bogusz <qboosh@...-linux.org>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---

This was supposed to have my Acked-by as well, I forgot to add it, sorry.

>  tools/lib/bpf/hashmap.h | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/tools/lib/bpf/hashmap.h b/tools/lib/bpf/hashmap.h
> index df59fd4fc95b..e0af36b0e5d8 100644
> --- a/tools/lib/bpf/hashmap.h
> +++ b/tools/lib/bpf/hashmap.h
> @@ -11,14 +11,18 @@
>  #include <stdbool.h>
>  #include <stddef.h>
>  #include <limits.h>
> -#ifndef __WORDSIZE
> -#define __WORDSIZE (__SIZEOF_LONG__ * 8)
> -#endif
>
>  static inline size_t hash_bits(size_t h, int bits)
>  {
>         /* shuffle bits and return requested number of upper bits */
> -       return (h * 11400714819323198485llu) >> (__WORDSIZE - bits);
> +#if (__SIZEOF_SIZE_T__ == __SIZEOF_LONG_LONG__)
> +       /* LP64 case */
> +       return (h * 11400714819323198485llu) >> (__SIZEOF_LONG_LONG__ * 8 - bits);
> +#elif (__SIZEOF_SIZE_T__ <= __SIZEOF_LONG__)
> +       return (h * 2654435769lu) >> (__SIZEOF_LONG__ * 8 - bits);
> +#else
> +#      error "Unsupported size_t size"
> +#endif
>  }
>
>  typedef size_t (*hashmap_hash_fn)(const void *key, void *ctx);
> --
> 2.24.1
>