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CAT:NONE; SFS:(13230031)(36860700004)(82310400014)(1800799015)(376005); DIR:OUT; SFP:1101; X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Apr 2024 15:32:58.9792 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 884581a2-a339-4a61-841b-08dc58aa55ff X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d; Ip=[63.35.35.123]; Helo=[64aa7808-outbound-1.mta.getcheckrecipient.com] X-MS-Exchange-CrossTenant-AuthSource: AM4PEPF00027A69.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV1PR08MB8451 X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libc-alpha-bounces+e=80x24.org@sourceware.org Hi,=0A= =0A= I like the general idea of more compact relocations, however what I don't g= et is=0A= what the overall goal is. If the goal is more compact object files, why don= 't we just=0A= add a (de)compress pass using a fast compression algorithm? CPU time is che= ap=0A= today, and real compression easily gives 2-4x reduction of object file size= , far more=0A= than you could achieve by just compressing relocations.=0A= =0A= Alternatively, if we wanted to access and process ELF files without any dec= ompression,=0A= we could define compact relocations as fixed-size entries. Using 64 bits fo= r a compact=0A= RELA relocation gives a straightforward 4x compression. Out of range values= could=0A= use the next entry to extend the ranges.=0A= =0A= So my main issue with the proposal is that it tries too hard to compress re= locations.=0A= For example using offset compression for relocations, symbol indices and ev= en addends=0A= seems to have little value: the signed offset means you lose one bit, and i= f out of range=0A= values are rare or not grouped together, offset encodings are actually less= efficient.=0A= =0A= I don't get the discussion about relocation numbers on AArch64 - 4 or 5 bit= s would=0A= handle all frequently used relocations, so we'd just remap them to fit in t= he short=0A= encoding. Hence I don't see a need at all for a signed offset encoding.=0A= =0A= So my suggestion is to either go for compression of the whole object file o= r use a=0A= simpler approach that isn't almost a compression algorithm.=0A= =0A= Cheers,=0A= Wilco=0A= =0A= =0A=