1 /* 2 File: CFMLateImport.h 3 4 Contains: Interface to CFM late import library. 5 6 Written by: Quinn 7 8 Copyright: Copyright � 1999 by Apple Computer, Inc., all rights reserved. 9 10 You may incorporate this Apple sample source code into your program(s) without 11 restriction. This Apple sample source code has been provided "AS IS" and the 12 responsibility for its operation is yours. You are not permitted to redistribute 13 this Apple sample source code as "Apple sample source code" after having made 14 changes. If you're going to re-distribute the source, we require that you make 15 it clear in the source that the code was descended from Apple sample source 16 code, but that you've made changes. 17 18 Change History (most recent first): 19 20 <6> 21/9/01 Quinn Changes for CWPro7 Mach-O build. 21 <5> 19/9/01 Quinn Change comments to reflect the fact that an unpacked data 22 section is no longer required. 23 <4> 19/9/01 Quinn Simplified API and implementation after a suggestion by Eric 24 Grant. You no longer have to CFM export a dummy function; you 25 can just pass in the address of your fragment's init routine. 26 <3> 16/11/00 Quinn Allow symbol finding via a callback and use that to implement 27 CFBundle support. 28 <2> 18/10/99 Quinn Renamed CFMLateImport to CFMLateImportLibrary to allow for 29 possible future API expansion. 30 <1> 15/6/99 Quinn First checked in. 31 */ 32 33 #pragma once 34 35 ///////////////////////////////////////////////////////////////// 36 37 // MoreIsBetter Setup 38 39 //#include "MoreSetup.h" 40 41 // Mac OS Interfaces 42 43 #if ! MORE_FRAMEWORK_INCLUDES 44 #include <MacTypes.h> 45 #include <CodeFragments.h> 46 #include <Devices.h> 47 #include <CFBundle.h> 48 #endif 49 50 ///////////////////////////////////////////////////////////////// 51 52 #ifdef __cplusplus 53 extern "C" { 54 #endif 55 56 /* FAQ 57 --- 58 59 Q: What does this library do? 60 A: It allows you to resolve a weak linked library at runtime, 61 by supply a CFM connection to the library that should substitute 62 for the weak linked one. 63 64 Q: Does the substituted library have to have the same name as the 65 weak linked library. 66 A: No. 67 68 Q: What's this useful for? 69 A: The most obvious example of where this is useful is when 70 you rely on shared libraries that the user might delete 71 or move. To can find the shared library (possibly even 72 using CatSearch), call GetDiskFragment to open a connection 73 to it, late import it using this library, and then the 74 rest of your code can continue to use the shared library 75 as if nothing had happened. No more defining thousands 76 of stub routines which call through routine pointers. 77 78 There are, however, numerous less obvious uses. You can 79 use this code to make a 'self repairing' application. If 80 the user removes your shared library from the Extensions 81 folder, the startup code for your application can offer 82 tor re-install it. If the user agrees, you can then 83 re-install your shared library, late import it, and then 84 continue running your application if nothing happened. 85 86 You can even use this code to free yourself from the 87 Extensions folder entirely. Say you have a suite of 88 applications that currently installs a dozen shared 89 libraries in the Extensions folder. You can move those 90 libraries to another folder entirely and each application's 91 startup code can track down the library (using an alias 92 in the Preferences file) and late import it. 93 94 An even cooler use is to provide easy abstraction layers. 95 Say you have a network code for both the MacTCP 96 API and the Open Transport API. Typically, you would be 97 force to do this by having an abstraction layer where every 98 routine contains a switch between MacTCP and OT. Your 99 OpenSocket routine might look like: 100 101 static int OpenSocket(void) 102 { 103 if (gOTAvailable) { 104 return OpenSocketOT(); 105 } else { 106 return OpenSocketMacTCP(); 107 } 108 } 109 110 With this code, you can avoid that entirely. Simply 111 weak link to a shared library that you know is never 112 going to be implemented ("crea;MySocketsDummy") and then, 113 at runtime, decide whether the system has MacTCP or OT 114 and late import the relevant real implementation 115 ("crea;MySocketsMacTCP" or "crea;MySocketsOT"). 116 One benefit of this approach is that only the MacTCP or 117 the OT code is resident in memory on any given system. 118 */ 119 120 typedef pascal OSStatus (*CFMLateImportLookupProc)(ConstStr255Param symName, CFragSymbolClass symClass, 121 void **symAddr, void *refCon); 122 // CFMLateImportLookupProc defines a callback for CFMLateImportCore. 123 // The routine is expected to look up the address of the symbol named 124 // symName and return it in *symAddr. The symbol should be of class 125 // symClass, although the callback decides whether a class mismatch is 126 // an error. refCon is an application defined value that was originally 127 // passed in to CFMLateImportCore. 128 // 129 // If this routine returns an error, a symbol address of 0 is assumed. 130 // If the symbol is marked as a weak import, the CFMLateImportCore will 131 // continue, otherwise the CFMLateImportCore routine will fail with the 132 // error. 133 134 extern pascal OSStatus CFMLateImportCore(const CFragSystem7DiskFlatLocator *fragToFixLocator, 135 CFragConnectionID fragToFixConnID, 136 CFragInitFunction fragToFixInitRoutine, 137 ConstStr255Param weakLinkedLibraryName, 138 CFMLateImportLookupProc lookup, 139 void *refCon); 140 // This routine will link you, at runtime, to some library 141 // that you were weak linked to and wasn't present when your 142 // fragment was prepared. As well as the obvious functionality 143 // of being able to resolve weak links after prepare time, 144 // this functionality can be put to a number of less obvious uses, 145 // some of which are discussed at the top of this header file. 146 // 147 // To call this routine, you need a number of pieces of information: 148 // 149 // 1. fragToFixLocator, fragToFixConnID: The location of your own 150 // code fragment on disk and the CFM connection ID to your own 151 // code fragment. Typically you get this information from your 152 // fragment's CFM init routine. You must ensure that 153 // fragToFixLocator->fileSpec points to an FSSpec of the 154 // file which holds your code fragment. 155 // 156 // IMPORTANT: 157 // The fact that you pass in a CFragSystem7DiskFlatLocator as the 158 // fragToFixLocator implies that the fragment to be fixed up must 159 // be in the data fork of a file. The code could be modified 160 // to remove this requirement, but on disk code fragments are the most 161 // common case. 162 // 163 // IMPORTANT: 164 // The fragment to fix may have a packed data section. Packing the 165 // data section will reduce the size of your fragment on disk, but it 166 // will significantly increase the memory needed by this routine 167 // (it increases memory usage by the sum of the sizes of the packed 168 // and unpacked data section). See below for instructions on how to 169 // create an unpacked data section. 170 // 171 // 2. fragToFixInitRoutine: A pointer to your own code fragment's 172 // fragment initialiser routine. You necessarily have one of these 173 // because you need it to get values for the fragToFixLocator and 174 // fragToFixConnID parameters. Just pass its address in as a parameter 175 // as well. 176 // 177 // 3. weakLinkedLibraryName: The name of the weak linked library which 178 // failed to link. You must have weak linked to this library. 179 // It is oxymoric for you to pass a strong linked library here, 180 // because your code would not have prepared if a strong linked 181 // library failed to prepare, and so you couldn't supply a valid 182 /// fragToFix. 183 // 184 // 4. lookup, refCon: A pointer to a callback function that the 185 // routine calls to look up the address of a symbol, and a refCon 186 // for that callback routine. 187 // 188 // Note: 189 // The fragToFixLocator and fragToFixInitRoutine parameters 190 // are artifacts of the way in which this functionality is implemented. 191 // In an ideal world, where CFM exported decent introspection APIs 192 // to third party developers, these parameters would not be necessary. 193 // If you're using this code inside Apple, you probably should investigate 194 // using the CFM private APIs for getting at the information these 195 // parameters are needed for. See the comments inside the implementation 196 // for more details. 197 // 198 // Note: 199 // The extra memory taken when you use a packed data section is also an 200 // artifact of my workaround for the lack of CFM introspection APIs. In 201 // my opinion it's better to use an unpacked data section and consume more 202 // space on disk while saving memory. In CodeWarrior you can switch to an 203 // unpacked data section by checking the "Expand Uninitialized Data" 204 // checkbox in the "PPC PEF" settings panel. In MPW, specified the 205 // "-packdata off" option to PPCLink. 206 // 207 // When the routine returns, any symbols that you imported from the 208 // library named weakLinkedLibraryName will be resolved to the address 209 // of the symbol provided by the "lookup" callback routine. 210 // 211 // It is possible for an unresolved import to remain unresolved after 212 // this routine returns. If the symbol import is marked as weak (as 213 // opposed to the library, which *must* be marked as weak) and the symbol 214 // is not found by the "lookup" callback, the routine will simple skip 215 // that symbol. If the symbol isn't marked as weak, the routine will fail 216 // in that case. 217 // 218 // Most of the possible error results are co-opted CFM errors. These 219 // include: 220 // 221 // cfragFragmentFormatErr -- The fragment to fix is is an unknown format. 222 // cfragNoSectionErr -- Could not find the loader section in the fragment to fix. 223 // cfragNoLibraryErr -- The fragment to fix is not weak linked to weakLinkedLibraryName. 224 // cfragFragmentUsageErr -- The fragment to fix doesn't have a data section. 225 // -- The fragment to fix is strong linked to weakLinkedLibraryName. 226 // -- The fragment doesn't have an init routine. 227 // cfragFragmentCorruptErr -- Encountered an undefined relocation opcode. 228 // unimpErr -- Encountered an unimplement relocation opcode. The 229 // relocation engine only implements a subset of the CFM 230 // relocation opcodes, the subset most commonly used by 231 // MPW and CodeWarrior PEF containers. If you encounter 232 // this error, you'll probably have to add the weird 233 // relocation opcode to the engine, which shouldn't be 234 // be too hard. 235 // memFullErr -- It's likely that this error is triggered by the memory 236 // needed to unpack your data section. Either make your 237 // data section smaller, or unpack it (see above). 238 // errors returned by FindSymbol 239 // errors returned by Memory Manager 240 // 241 // The routine needs enough memory to hold the loader section of the fragment 242 // to fix in memory. It allocates that memory using NewPtr and dispsoses of 243 // it before it returns. You may want to change the memory allocator, which 244 // is very simple. 245 246 extern pascal OSStatus CFMLateImportLibrary(const CFragSystem7DiskFlatLocator *fragToFixLocator, 247 CFragConnectionID fragToFixConnID, 248 CFragInitFunction fragToFixInitRoutine, 249 ConstStr255Param weakLinkedLibraryName, 250 CFragConnectionID connIDToImport); 251 // A wrapper around CFMLateImportCore that looks up symbols by calling 252 // FindSymbol on a connection to a CFM library (connIDToImport). 253 // You can get this connection ID through any standard CFM API, for example 254 // GetSharedLibrary, GetDiskFragment, or GetMemFragment. 255 // 256 // IMPORTANT: 257 // The fragment name for connIDToImport *does not* have to match 258 // weakLinkedLibraryName. This is part of the power of this library. 259 260 extern pascal OSStatus CFMLateImportBundle(const CFragSystem7DiskFlatLocator *fragToFixLocator, 261 CFragConnectionID fragToFixConnID, 262 CFragInitFunction fragToFixInitRoutine, 263 ConstStr255Param weakLinkedLibraryName, 264 CFBundleRef bundleToImport); 265 // A wrapper around CFMLateImportCore that looks up symbols by calling 266 // CFBundleGetFunctionPointerForName on a reference to a Core Foundation 267 // bundle (bundleToImport). You can get this reference through any 268 // Core Foundation bundle API, for example CFBundleCreate. 269 270 #ifdef __cplusplus 271 } 272 #endif 273