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From: Bart Van Assche <Bart.VanAssche@wdc.com>
To: "jejb@linux.vnet.ibm.com" <jejb@linux.vnet.ibm.com>,
	"steve@sk2.org" <steve@sk2.org>, "hare@suse.com" <hare@suse.com>,
	"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
	"axboe@kernel.dk" <axboe@kernel.dk>
Cc: "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"kernel-hardening@lists.openwall.com"
	<kernel-hardening@lists.openwall.com>
Subject: Re: [PATCH] scsi: resolve COMMAND_SIZE at compile time
Date: Fri, 9 Mar 2018 22:47:12 +0000	[thread overview]
Message-ID: <1520635631.2907.16.camel@wdc.com> (raw)
In-Reply-To: <20180309223355.21222-1-steve@sk2.org>

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WARNING: multiple messages have this Message-ID (diff)
From: Bart Van Assche <Bart.VanAssche@wdc.com>
To: "jejb@linux.vnet.ibm.com" <jejb@linux.vnet.ibm.com>,
	"steve@sk2.org" <steve@sk2.org>, "hare@suse.com" <hare@suse.com>,
	"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
	"axboe@kernel.dk" <axboe@kernel.dk>
Cc: "linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"kernel-hardening@lists.openwall.com"
	<kernel-hardening@lists.openwall.com>
Subject: Re: [PATCH] scsi: resolve COMMAND_SIZE at compile time
Date: Fri, 9 Mar 2018 22:47:12 +0000	[thread overview]
Message-ID: <1520635631.2907.16.camel@wdc.com> (raw)
In-Reply-To: <20180309223355.21222-1-steve@sk2.org>

On Fri, 2018-03-09 at 23:33 +0100, Stephen Kitt wrote:
> +/*
> + * SCSI command sizes are as follows, in bytes, for fixed size commands, per
> + * group: 6, 10, 10, 12, 16, 12, 10, 10. The top three bits of an opcode
> + * determine its group.
> + * The size table is encoded into a 32-bit value by subtracting each value
> + * from 16, resulting in a value of 1715488362
> + * (6 << 28 + 6 << 24 + 4 << 20 + 0 << 16 + 4 << 12 + 6 << 8 + 6 << 4 + 10).
> + * Command group 3 is reserved and should never be used.
> + */
> +#define COMMAND_SIZE(opcode) \
> +	(16 - (15 & (1715488362 >> (4 * (((opcode) >> 5) & 7)))))

To me this seems hard to read and hard to verify. Could this have been written
as a combination of ternary expressions, e.g. using a gcc statement expression
to ensure that opcode is evaluated once?

Thanks,

Bart.



  reply	other threads:[~2018-03-09 22:47 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-09 22:29 VLA removal, device_handler and COMMAND_SIZE Stephen Kitt
2018-03-09 22:32 ` [PATCH] device_handler: remove VLAs Stephen Kitt
2018-03-09 22:48   ` Bart Van Assche
2018-03-09 22:48     ` Bart Van Assche
2018-03-10 13:14     ` Stephen Kitt
2018-03-12 15:41       ` Bart Van Assche
2018-03-12 15:41         ` Bart Van Assche
2018-03-12 19:26         ` Stephen Kitt
2018-03-12  6:25   ` Hannes Reinecke
2018-03-13  2:37   ` Martin K. Petersen
2018-03-09 22:33 ` [PATCH] scsi: resolve COMMAND_SIZE at compile time Stephen Kitt
2018-03-09 22:47   ` Bart Van Assche [this message]
2018-03-09 22:47     ` Bart Van Assche
2018-03-10 13:29     ` Stephen Kitt
2018-03-10 20:49       ` James Bottomley
2018-03-10 21:16         ` Douglas Gilbert
2018-03-11 15:01         ` Stephen Kitt
2018-03-11 15:01           ` Stephen Kitt
2018-03-13 11:34   ` David Laight
2018-03-13 11:34     ` David Laight

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