iOS 15 如何让 App 启动更快？

% xcrun dyldinfo -rebase -bind Snapchat.app/Snapchatrebase information (from compressed dyld info):segment section address type__DATA __got 0x10748C0C8 pointer...bind information:segment section address type addend dylib symbol__DATA __const 0x107595A70 pointer 0 libswiftCore _$sSHMp

% otool -l iOS14Example.app/iOS14Example | grep LC_DYLD      cmd LC_DYLD_INFO_ONLY% otool -l iOS15Example.app/iOS15Example | grep LC_DYLD      cmd LC_DYLD_CHAINED_FIXUPS      cmd LC_DYLD_EXPORTS_TRIE

let bytes = (try! Data(contentsOf: url) as NSData).bytes      bytes.processLoadComands { load_command, pointer in        if load_command.cmd == LC_DYLD_EXPORTS_TRIE {          let dataCommand = pointer.load(as: linkedit_data_command.self)          bytes.advanced(by: Int(dataCommand.dataoff)).readExportTrie()        }      }    
  extension UnsafeRawPointer {        func readExportTrie() {          var frontier = readNode(name: "")          guard !frontier.isEmpty else { return }    
      repeat {            let (prefix, offset) = frontier.removeFirst()            let children = advanced(by: Int(offset)).readNode(name: prefix)            for (suffix, offset) in children {              frontier.append((prefix + suffix, offset))            }          } while !frontier.isEmpty        }    
    // Returns an array of child nodes and their offset        func readNode(name: String) -> [(String, UInt)] {          guard load(as: UInt8.self) == 0 else {            // This is a terminal node            print("symbol name \(name)")            return []          }          let numberOfBranches = UInt(advanced(by: 1).load(as: UInt8.self))          var mutablePointer = self.advanced(by: 2)          var result = [(String, UInt)]()          for _ in 0..<numberOfBranches {            result.append(              (mutablePointer.readNullTerminatedString(),               mutablePointer.readULEB()))          }          return result        }      }

struct dyld_chained_ptr_64_rebase{uint64_t target : 36,high8 : 8,reserved : 7, // 0snext : 12,bind : 1; // Always 0 for a rebase};

% xcrun dyldinfo -rebase Snapchat.app/Snapchat > rebases% ruby -e 'puts IO.read("rebases").split("\n").drop(2).map { |a| a.split(" ")[2].to_i(16) / 16384 }.uniq.count'1554% xcrun dyldinfo -bind Snapchat.app/Snapchat > binds450