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Message-ID: <02c609d2-096c-79ba-823b-46490dd00c04@suse.com> Date: Thu, 30 Mar 2023 10:52:21 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH 4/5] multiboot2: parse console= option when setting GOP mode Content-Language: en-US To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Cc: marmarek@invisiblethingslab.com, Andrew Cooper , Wei Liu , xen-devel@lists.xenproject.org, Daniel Kiper References: <20221123154525.63068-1-roger.pau@citrix.com> <20221123154525.63068-5-roger.pau@citrix.com> <8f7e0393-8c0f-a924-7cee-25b9fca6f739@suse.com> <8fb2f771-3354-3f52-f923-e7fe7861cfbf@suse.com> From: Jan Beulich In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR3P281CA0024.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:1c::15) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|AS8PR04MB9192:EE_ X-MS-Office365-Filtering-Correlation-Id: 443b3249-8c7e-4759-c956-08db30fc1422 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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And how do you guarantee this? >>> >>> I think the comment is misleading, must be the last checked for tag in >>> the loop that does this in assembly, because it's not using cmove. >>> I've adjusted to: >>> >>> /* Get command line from Multiboot2 information. */ >>> cmpl $MULTIBOOT2_TAG_TYPE_CMDLINE,MB2_tag_type(%rcx) >>> jne .Lno_cmdline >>> lea MB2_tag_string(%rcx),%rdx >>> jmp .Lefi_mb2_next_tag >>> .Lno_cmdline: >>> >>> Maybe there's some instruction I'm missing similar to a conditional >>> lea? >> >> There isn't. If you want to get away without conditional branch, then >> you'll need to LEA to a scratch register (unconditional) and then >> CMOVcc from that scratch register. > > Likely not worth it, unless you dislike the extra conditional branch. Entirely up to you - I'm fine either way. Jan