NAME
NSModule - programmatic interface for working with modules and symbols
SYNOPSIS
#include
typedef void * NSModule;
extern NSModule NSLinkModule(
NSObjectFileImage objectFileImage, const char *moduleName, unsigned long options); extern enum DYLDBOOL NSUnLinkModule(NSModule module,
unsigned long options); extern const char * NSNameOfModule(NSModule m);
extern const char * NSLibraryNameForModule(NSModule m);
typedef void * NSSymbol; extern enum DYLDBOOL NSIsSymbolNameDefined( const char *symbolName); extern enum DYLDBOOL NSIsSymbolNameDefinedWithHint( const char *symbolName const char *libraryNameHint); extern enum DYLDBOOL NSIsSymbolNameDefinedInImage( const struct machheader *image, const char *symbolName); extern NSSymbol NSLookupAndBindSymbol( const char *symbolName); extern NSSymbol NSLookupAndBindSymbolWithHint( const char *symbolName const char *libraryNameHint); extern NSSymbol NSLookupSymbolInModule(NSModule module,
const char *symbolName); extern NSSymbol NSLookupSymbolInImage( const struct machheader *image, const char *symbolName, unsigned long options); extern const char * NSNameOfSymbol( NSSymbol symbol); extern void * NSAddressOfSymbol( NSSymbol symbol);extern NSModule NSModuleForSymbol(
NSSymbol symbol); extern enum DYLDBOOL NSAddLibrary( const char *pathName); extern enum DYLDBOOL NSAddLibraryWithSearching( const char *pathName); extern const struct machheader * NSAddImage( const char *imagename, unsigned long options); extern long NSVersionOfRunTimeLibrary( const char *libraryName); extern long NSVersionOfLinkTimeLibrary( const char *libraryName); extern int NSGetExecutablePath( char *buf, unsigned long *bufsize) extern void NSInstallLinkEditErrorHandlers( NSLinkEditErrorHandlers *handlers); extern void NSLinkEditError( NSLinkEditErrors *c, int *errorNumber, const char **fileName, const char **errorString);extern NSModule NSReplaceModule(
NSModule moduleToReplace,
NSObjectFileImage newObjectFileImage, unsigned long options); These routines are the programmatic interface for working with modules and symbols in a program. A program is composed of a set of images, an executable, plugins, and dynamic shared libraries. An image which isan executable or a plugin is composed of one module containing a col-
lection of symbols. A dynamic shared library is composed of one ormore modules with each of those modules containing a separate collec-
tion of symbols. If a symbol is used from a module then all the sym-
bols from that module are used. When a program is executed it selectively binds the symbols it needs from the modules in the dynamic libraries that are loaded. Normally a program is staticly linked against a set of dynamic shared libraries when it is built. So when the program is executed the dynamic linker will automaticly load those dynamic shared libraries. A program may programmatically load plugins after it starts executing and that is done with two sets of API's. The first is the API's of NSObjectFileImage(3) and the second is NSLinkModule. Unlike modules in the dynamic libraries when a plugin is loaded it is not selectively bound to but always bound into the program. NSLinkModule links the specified object file image into the program andreturns the module handle for it. Currently the implementation is lim-
ited to only Mach-O MHBUNDLE types which are used for plugins. A mod-
ule name is specified when a module is linked so that later NSNameOf-
Module can be used with the module handle and to do things like reporterrors. If you want gdb(1) to be able to debug your module, when call-
ing NSLinkModule you should pass the image path as the module name. When a module is linked, all libraries referenced by the module are added to the list of libraries to be searched. The parameter, options, can have a set of options or'ed together. The options for NSLinkModule are as follows: NNSSLLIINNKKMMOODDUULLEEOOPPTTIIOONNNNOONNEE This specifies no options. With this the global symbols fromthe module are made part of the global symbol table of the pro-
gram. If any errors occur the handlers installed with NSInstal-
lLinkEditErrorHandlers are called or the default action is taken if there are no handlers. NNSSLLIINNKKMMOODDUULLEEOOPPTTIIOONNBBIINNDDNNOOWW This option causes the dynamic link editor to bind all undefined references for the loaded module and not allow references to be bound as needed. This affects all the references in the module and all of the dependent references. NNSSLLIINNKKMMOODDUULLEEOOPPTTIIOONNPPRRIIVVAATTEE With this option the global symbols from the module are not madepart of the global symbol table of the program. The global sym-
bols of the module can then be looked up using NSLookupSymbolIn-
Module. NNSSLLIINNKKMMOODDUULLEEOOPPTTIIOONNRREETTUURRNNOONNEERRRROORR With this option if errors occur while binding this module it is automaticly unloaded and NULL is returned as the module handle. To get the error information for the module that failed to load the routine NSLinkEditError is then used. It has the same parameters as the link edit error handler (see below) except all the parameters are pointers in which the information is returned indirectly. NNSSLLIINNKKMMOODDUULLEEOOPPTTIIOONNDDOONNTTCCAALLLLMMOODDIINNIITTRROOUUTTIINNEESS With this option the module init routines are not called. Thisis only useful to the fix-and-continue implementation.
NSLINKMODULEOPTIONTRAILINGPHYSNAME
With this option the parameter, moduleName is assumed to be a string with the logical name of the image with the physical nameof the object file tailing after the NULL character of the logi-
cal name. This is only useful to the zero-link implementation.
NSUnLinkModule unlinks the specified module handle from the program. Currently the implementation is limited to only allow modules linked with NSLinkModule to be unlinked. The parameter, options, can have a set of options or'ed together. The options for NSUnLinkModule are as follows: NNSSUUNNLLIINNKKMMOODDUULLEEOOPPTTIIOONNNNOONNEE This specifies no options. With this the module is unlinked from the program and the memory for the module is deallocated.If any errors occur the handlers installed with NSInstal-
lLinkEditErrorHandlers are called or the default action is taken if there are no handlers. NNSSUUNNLLIINNKKMMOODDUULLEEOOPPTTIIOONNKKEEEEPPMMEEMMOORRYYMMAAPPPPEEDD With this option the memory for the module is not deallocated allowing pointers into the module to still be valid.NSUNLINKMODULEOPTIONRESETLAZYREFERENCES
With this option any lazy references (direct function calls) to symbols defined in the module are reset to be bound on first call again and not cause any undefined symbol errors. Currently this is only implemented for the PowerPC architecture. NSNameOfModule is passed a module handle and returns the name of the module. If the module handle is invalid NULL is returned. NSLibraryNameForModule is passed a module handle and returns the name of the library the module is in if any. If the module handle is for a module that is not in a library (in the executable or a plugin) or the module handle is invalid NULL is returned.NSIsSymbolNameDefined is passed a global symbol name (global 'C' sym-
bols names are preceded with an underbar '') and returns TRUE or FALSE based on if the symbol is defined in the program's global symbol table. If the symbol is not defined no error occurs. NSIsSymbolNameDefinedWithHint is the same as NSIsSymbolNameDefined but the libraryNameHint parameter provides a hint as to where to start the lookup in a prebound program. The libraryNameHint parameter is matched up with the actual library install names with strstr(3). NSIsSymbolNameDefinedInImage is passed a pointer to the machheader of a machheader structure of a dynamic library being used by the program and a symbol name. This returns TRUE or FALSE based on if the symbolis defined in the specified image or one of the image's sub-frameworks
or sub-umbrellas. If the program was built with the ld(1)
-ffoorrcceeffllaattnnaammeessppaaccee flag or executed with the environment variable
DYLDFORCEFLATNAMESPACE set and the pointer to a machheader struc-
ture is not of a bundle loaded with the NNSSLLIINNKKMMOODDUULLEEOOPPTTIIOONNPPRRIIVVAATTEE option of NSLinkModule(3) then the pointer to a machheader is ignoredand the symbol is looked up in all the images using the first defini-
tion if found.The image handle parameter for NSLookupSymbolInImage and NSIsSymbol-
NameDefinedInImage is a pointer to a read-only mach header structure of
a dynamic library being used by the program. Besides the NSAddImage(3) routine the pointer to a mach header can also be obtained by using alink editor defined symbol as in
ld(1) man page. Also the dyld(3) routine dyldgetimageheader(3) and the machheader pointer arguments to the call back routines called from dyldregisterfuncforaddimage(3) routines can also be used. NSLookupAndBindSymbol is passed a global symbol name and looks up andand described on the binds the symbol into the program. It returns an NSSymbol for the sym-
bol. If any errors occur the handlers installed with NSInstal-
lLinkEditErrorHandlers are called or the default action is taken if there are no handlers. NSLookupAndBindSymbolWithHint is the same as NSLookupAndBindSymbol but the libraryNameHint parameter provides a hint as to where to start the lookup in a prebound program. The libraryNameHint parameter is matched up with the actual library install names with strstr(3). NSLookupSymbolInModule is passed a symbol name and a module handle and looks up the symbol in that module. Currently this is only implemented for module handles returned with NSLinkModule. If the symbol is found an NSSymbol for the symbol is returned otherwise NULL is returned and no error occurs. NSLookupSymbolInImage is passed a pointer to a machheader structure of a dynamic library being used by the program and a symbol name. It returns an NSSymbol for the symbol for defined in the specified imageor the image's sub-frameworks or sub-umbrellas. If the program was
built with the ld(1) -ffoorrcceeffllaattnnaammeessppaaccee flag or executed with the
environment variable DYLDFORCEFLATNAMESPACE set and the pointer to a
machheader structure is not of a bundle loaded with the NNSSLLIINNKKMMOODD-
UULLEEOOPPTTIIOONNPPRRIIVVAATTEE option of NSLinkModule(3) then the pointer to a machheader is ignored and the symbol is looked up in all the imagesusing the first definition found. If the option NSLOOKUPSYMBOLINIM-
AGEOPTIONRETURNONERROR is not used if any errors occur the handlers
installed with NSInstallLinkEditErrorHandlers are called or the defaultaction is taken if there are no handlers. The options of NSLookupSym-
bolInImage are as follows: NNSSLLOOOOKKUUPPSSYYMMBBOOLLIINNIIMMAAGGEEOOPPTTIIOONNBBIINNDDJust bind the non-lazy symbols of module that defines the sym-
bolName and let all lazy symbols in the module be bound on firstcall. This should be used in the normal case for a trusted mod-
ule expected to bind without any errors like a module in a sys-
tem supplied library. NNSSLLOOOOKKUUPPSSYYMMBBOOLLIINNIIMMAAGGEEOOPPTTIIOONNBBIINNDDNNOOWWBind all the non-lazy and lazy symbols of module that defines
the symbolName and let all dependent symbols in the needed libraries be bound as needed. This would be used for a module that might not be expected bind without errors but links againstonly system supplied libraries which are expected to bind with-
out any errors. NNSSLLOOOOKKUUPPSSYYMMBBOOLLIINNIIMMAAGGEEOOPPTTIIOONNBBIINNDDFFUULLLLYY Bind all the symbols of the module that defines the symbolName and all the dependent symbols of all needed libraries. This should only be used for things like signal handlers and linkedit error handlers that can't bind other symbols when executing to handle the signal or error. NNSSLLOOOOKKUUPPSSYYMMBBOOLLIINNIIMMAAGGEEOOPPTTIIOONNRREETTUURRNNOONNEERRRROORR With this option if errors occur while binding the module that defines the symbolName then the module is automaticly unloadedand NULL is returned as the NSSymbol. To get the error informa-
tion for why the module that failed to bind the routine NSLinkEditError is then used. It has the same parameters as the link edit error handler (see below) except all the parameters are pointers in which the information is returned indirectly.NSNameOfSymbol is passed an NSSymbol and returns the name of the sym-
bol. NSAddressOfSymbol is passed an NSSymbol and returns the address of the symbol.NSModuleForSymbol is passed an NSSymbol and returns the NSModule that
symbol is defined in. NSAddLibrary is passed the file name of a dynamic shared library to be added to the search list. If it is successful it returns TRUE else it returns FALSE. NSAddLibraryWithSearching is passed the file name of a dynamic shared library to be added to the search list the file name passed will be effected by the various DYLD environment variables as if this library were linked into the program. If it is successful it returns TRUE else it returns FALSE. NSAddImage is passed the file name of a dynamic shared library to be added to the search list of the program if not already loaded. It returns a pointer to the machheader structure of the dynamic library being used by the program. For best performance of this routine if the library is expected to be already loaded by the program the imagename should be a full path name and the same as the name recorded by the program. If it is a symlink then an open(2) and an fstat(2) are needed to determine it is the same file as one already loaded. If the dynamic shared library has not already been loaded it along withall the needed dependent libraries are loaded. With the options param-
eter NSADDIMAGEOPTIONNONE then any error in loading will cause the
linkEdit error handler set by NSInstallLinkEditErrorHandlers(3) to be called or the default action of printing the error and exiting to be taken. The other options of NSAddImage are as follows: NNSSAADDDDIIMMAAGGEEOOPPTTIIOONNRREETTUURRNNOONNEERRRROORR With this option if errors occur while loading this library it is automatically unloaded and NULL is returned. To get theerror information for the library that failed to load the rou-
tine NSLinkEditError is then used. It has the same parametersas the link edit error handler (see below) except all the param-
eters are pointers in which the information is returned indi-
rectly. NNSSAADDDDIIMMAAGGEEOOPPTTIIOONNWWIITTHHSSEEAARRCCHHIINNGG With this option the imagename passed for the library and all its dependents will be effected by the various DYLD environment variables as if this library were linked into the program. NNSSAADDDDIIMMAAGGEEOOPPTTIIOONNRREETTUURRNNOONNLLYYIIFFLLOOAADDEEDD With this option if the imagename passed for the library has not already been loaded it is not loaded. Only if it has been loaded the pointer to the machheader will not be NULL.NSADDIMAGEOPTIONMATCHFILENAMEBYINSTALLNAME
When this option is specified if a later load of a dependent dynamic library with a file system path is needed by an image that matches the install name of the dynamic library loaded with this option, then the dynamic library loaded with the call to NSAddImage() is used in place of the dependent dynamic library. NSVersionOfRunTimeLibrary is passed the install name of a dynamic shared library and returns currentversion number of the library theprogram is using or -1 if the program is not using that library.
NSVersionOfLinkTimeLibrary is passed the install name of a dynamic shared library and returns the currentversion number of the librarythe executable program was built with or -1 if the program was not
built with that library. NSGetExecutablePath copies the path of the executable into the buffer and returns 0 if the path was successfully copied in the providedbuffer. If the buffer is not large enough, -1 is returned and the
expected buffer size is copied in *bufsize. Note that NSGetExe-
cutablePath will return "a path" to the executable not a "real path" to the executable. That is the path may be a symbolic link and not the real file. And with deep directories the total bufsize needed could be more than MAXPATHLEN. EERRRROORR HHAANNDDLLIINNGGNSInstallLinkEditErrorHandlers is passed a pointer to a NSLinkEditEr-
rorHandlers which contains three function pointers to be used for han-
dling dynamic link errors. The prototypes for these functions are given in the following typedef: typedef struct { void (*undefined)(const char *symbolName);NSModule (*multiple)(NSSymbol s, NSModule oldModule, NSModule newModule);
void (*linkEdit)(NSLinkEditErrors errorClass, int errorNumber, const char *fileName, const char *errorString); } NSLinkEditErrorHandlers; The first two functions allow the programmer to direct the link edit processing of undefined symbols and multiply defined symbols. The third function allows the programmer to catch all other link editor errors. The state when one of the user error functions gets called will be such that no module will be partially loaded (except in the case of resource errors like out of memory and other relocation errors). However, with undefined symbol errors those modules referencing undefined symbols will be partially bound, and use of such modules can and will crash the program. Great care should be taken when implementing these functions, as the program is running in a state that will crash if it uses an unbound symbol. To be safe, these functions should only rely on other things in the same module or in the executable. If the user does not supply these functions, the default will be to write an error message on to file descriptor 2 (usually stderr) and exit the program (except for the linkEdit error handler when the NSLinkEditErrors is NSLinkEditWarningError, then the default is to do nothing). The specified undefined handler may make calls to any of the runtime loading functions to add modules based on the undefined symbol name. After dealing with this symbol name successfully (by doing a runtimeloading operation to resolve the undefined reference) the handler sim-
ply returns. If more symbol's names remain undefined the handler will be called repeatedly with an undefined symbol name. If the handler can't deal with the symbol it should not return (put up a panel, abort, etc) and cause the program to exit. Or it can remove itself as the undefined handler and return which will cause the default action of printing the undefined symbol names and exiting. The specified multiply defined symbol handler is called during the process of runtime linking and thus it may not call any of the runtimeloading functions as only one set of linking operations can be per-
formed in the task at a time. The only programmatic functions that can be called from a multiply defined symbol handler are NSNameOfSymbol, NSNameOfModule and NSLibraryNameForModule (provided they are linked into the program before the handler is called). This handler returns the module handle for the symbol that is to be used for further link editing, either the oldModule or the newModule. It may also record one of the module handles to later take action after the runtime linking process has completed (for example later unlink the module). The dynamic link editor updates the references to the symbol if the handler specifies the new symbol is to be used. The references which areupdated are those that the compiler system generated as indirect refer-
ences. Initialized data and references that were created at runtime are not effected. The specified linkEdit error handler is called for all other runtime linking errors. These other runtime linking errors are either warnings or fatal errors. If the user's link edit error handler function returns for a fatal error it will cause the program to exit. There is small set of major error classes which have specific error numbers. These numbers are be passed in the parameter errorClass. These major error classes include: typedef enum { NSLinkEditFileAccessError, NSLinkEditFileFormatError, NSLinkEditMachResourceError, NSLinkEditUnixResourceError, NSLinkEditOtherError, NSLinkEditWarningError, NSLinkEditMultiplyDefinedError, NSLinkEditUndefinedError } NSLinkEditErrors;For the error class NSLinkEditUnixResourceError the errorNumber parame-
ter will be an errno value (see intro(2)). For the error class NSLinkEditMachResourceError the errorNumber parameter will be a kernreturnt value. For the error class NSLinkEditOtherError the errorNumber parameter will be a one of the following values: typedef enum { NSOtherErrorRelocation, NSOtherErrorLazyBind, NSOtherErrorIndrLoop, NSOtherErrorLazyInit, NSOtherErrorInvalidArgs } NSOtherErrorNumbers; For all errors, an attempt to pass an error string will be made. In some cases such as resource errors, it may not be possible to return a string. In those cases the errorString parameter will be For file access errors and file format errors, an attempt to return a file name will also be passed, and if that is not possible the filename parameter will be AALLSSOO SSEEEE NSObjectFileImage(3), dyld(3)Apple Computer, Inc. October 6, 2003 NSModule(3)