linux-kernel - RE: [PATCH] net/sctp: fix GCC8+ -Wpacked-not-aligned warnings

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Message-ID: <158b26b6f3b24164aceacd2428095315@AcuMS.aculab.com>
Date:   Mon, 29 Jul 2019 10:39:16 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Qian Cai' <cai@....pw>,
        "vyasevich@...il.com" <vyasevich@...il.com>,
        "nhorman@...driver.com" <nhorman@...driver.com>,
        "marcelo.leitner@...il.com" <marcelo.leitner@...il.com>
CC:     "linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] net/sctp: fix GCC8+ -Wpacked-not-aligned warnings

From: Qian Cai
> Sent: 26 July 2019 21:58
> 
> There are a lot of those warnings with GCC8+ 64bit,
> 
...
> Fix them by aligning the structures and fields to 8 bytes instead.
...
>  struct sctp_setpeerprim {
>  	sctp_assoc_t            sspp_assoc_id;
> -	struct sockaddr_storage sspp_addr;
> -} __attribute__((packed, aligned(4)));
> +	struct sockaddr_storage sspp_addr __attribute__((aligned(8)));
> +} __attribute__((packed, aligned(8)));

What happens to this one if you change both to aligned(4) ?
Much the same way as:
	struct {
		int a;
		long b __attribute__((aligned(4));
	};
is only 12 bytes on (most) 64bit systems.

	David

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