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RE: [PATCH net] tcp: avoid bogus gcc-7 array-bounds warning

From David Laight <David.Laight@ACULAB.COM>
Newsgroups linux.kernel
Subject RE: [PATCH net] tcp: avoid bogus gcc-7 array-bounds warning
Date 2017-07-28 17:50 +0200
Message-ID <u8fGx-5Cs-5@gated-at.bofh.it> (permalink)
References <u8eKv-4ZB-29@gated-at.bofh.it>
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From: Arnd Bergmann
> Sent: 28 July 2017 15:42
...
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -2202,9 +2202,10 @@ static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb,
>  static void tcp_chrono_set(struct tcp_sock *tp, const enum tcp_chrono new)
>  {
>  	const u32 now = tcp_jiffies32;
> +	enum tcp_chrono old = tp->chrono_type;
> 
> -	if (tp->chrono_type > TCP_CHRONO_UNSPEC)
> -		tp->chrono_stat[tp->chrono_type - 1] += now - tp->chrono_start;
> +	if (old > TCP_CHRONO_UNSPEC)
> +		tp->chrono_stat[old - 1] += now - tp->chrono_start;
>  	tp->chrono_start = now;
>  	tp->chrono_type = new;

What a horrid combination of enum and integers.
Also have u32 chrono_stat[3]; - should probably be [__TCP_CHRONO_MAX - 1]
(or - CHRONO_FIRST which is defined to be 1).

Checking if (old != 0) would make the code more readable.

	David

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Thread

[PATCH net] tcp: avoid bogus gcc-7 array-bounds warning Arnd Bergmann <arnd@arndb.de> - 2017-07-28 16:50 +0200
  RE: [PATCH net] tcp: avoid bogus gcc-7 array-bounds warning David Laight <David.Laight@ACULAB.COM> - 2017-07-28 17:50 +0200
  Re: [PATCH net] tcp: avoid bogus gcc-7 array-bounds warning David Miller <davem@davemloft.net> - 2017-07-30 08:30 +0200

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