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Message-ID: Date: Tue, 14 Mar 2023 07:30:44 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH] Drop ELF notes from non-EFI binary too To: =?UTF-8?Q?Marek_Marczykowski-G=c3=b3recki?= Cc: Andrew Cooper , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Wei Liu , xen-devel@lists.xenproject.org References: <20230225235642.38880-1-marmarek@invisiblethingslab.com> <9fbbfa17-821f-8c9e-376e-911481a1988b@suse.com> Content-Language: en-US From: Jan Beulich In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR2P281CA0139.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:9e::10) To VE1PR04MB6560.eurprd04.prod.outlook.com (2603:10a6:803:122::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VE1PR04MB6560:EE_|AM7PR04MB7126:EE_ X-MS-Office365-Filtering-Correlation-Id: 40691010-65a6-4d72-1042-08db2455a4fc X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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With CET-related notes, >>> which use 64bit fields, this results in 32bit binary with corrupted >>> notes. Drop them all (except build-id and PVH note retained >>> explicitly). >>> >>> Suggested-by: Jan Beulich >> >> Perhaps a misunderstanding: Yes, I did suggest this as a possibility, >> but I didn't really mean we actually do so. At the very least not >> without further clarifying what the cons of doing so are. The notes, >> after all, are actually valid in xen-syms; they become bogus in the >> course of mkelf32's processing. >> >>> --- a/xen/arch/x86/xen.lds.S >>> +++ b/xen/arch/x86/xen.lds.S >>> @@ -192,13 +192,6 @@ SECTIONS >>> #endif >>> #endif >>> >>> -#ifndef EFI >>> - /* Retain these just for the purpose of possible analysis tools. */ >>> - DECL_SECTION(.note) { >>> - *(.note.*) >>> - } PHDR(note) PHDR(text) >>> -#endif >>> - >>> _erodata = .; >>> >>> . = ALIGN(SECTION_ALIGN); >> >> Is this sufficient? .note.* isn't part of DISCARD_SECTIONS except for >> xen.efi. I would expect it needs to move there from DISCARD_EFI_SECTIONS. >> Otherwise, aiui, the linker's orphan section placement will kick in. > > What supposedly happens then? By looking at binary produced with this > patch, I don't see other .note sections included. The linker can't really discard them without being told so, from all I know. So the pieces must land somewhere, and considering the special section type (SHT_NOTE) I would find it odd if they were folded into some other section. >> Yet >> at that point you'd also affect Arm and RISC-V (which, interestingly, >> don't place .note.* anywhere at all right now, afaics). > > That's interesting observation. For RISC-V, I'm not surprised given how > fresh it is in tree, but if Arm doesn't need it either, maybe adding to > DISCARD_SECTIONS isn't such a bad idea? Well, yes, if we want to get rid of them, putting them there makes sense. First we need to figure where the notes end up when not placed explicitly (as that'll tell us whether on Arm they can be useful at all right now). Jan