linux-kernel - Re: [RFC PATCH] libbpf: Change hash_combine parameters from long to _

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Message-ID: <CAEf4BzYape9gtc7k1NQMD5BrfakzDXV_9SHNqZeamcaSKn744Q@mail.gmail.com>
Date: Fri, 15 Nov 2024 11:57:24 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Sidong Yang <sidong.yang@...iosa.ai>
Cc: Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] libbpf: Change hash_combine parameters from long to __u32

On Fri, Nov 15, 2024 at 2:51 AM Sidong Yang <sidong.yang@...iosa.ai> wrote:
>
> The hash_combine() could be trapped when compiled with sanitizer like "zig cc".
> This patch changes parameters to __u32 to fix it.

Can you please elaborate? What exactly are you fixing? "Undefined"
signed integer overflow? I can consider changing long to unsigned
long, but I don't think we should downgrade from long all the way to
32-bit u32. I'd rather keep all those 64 bits for hash.

pw-bot: cr

>
> Signed-off-by: Sidong Yang <sidong.yang@...iosa.ai>
> ---
>  tools/lib/bpf/btf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 8befb8103e32..11ccb5aa4958 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -3548,7 +3548,7 @@ struct btf_dedup {
>         struct strset *strs_set;
>  };
>
> -static long hash_combine(long h, long value)
> +static __u32 hash_combine(__u32 h, __u32 value)
>  {
>         return h * 31 + value;
>  }
> --
> 2.42.0
>
>