NSModule(3)

NAME
NSModule - programmatic interface for working with modules and symbols

SYNOPSIS

#include <mach-o/dyld.h>

typedef void * NSModule;

extern NSModule NSLinkModule(
	NSObjectFileImage objectFileImage,
	const char *moduleName,
	unsigned long options);

extern enum DYLD_BOOL NSUnLinkModule(
	NSModule module,
	unsigned long options);

extern const char * NSNameOfModule(
	NSModule m);

extern const char * NSLibraryNameForModule(
	NSModule m);

typedef void * NSSymbol;

extern enum DYLD_BOOL NSIsSymbolNameDefined(
	const char *symbolName);

extern enum DYLD_BOOL NSIsSymbolNameDefinedWithHint(
	const char *symbolName
	const char *libraryNameHint);

extern enum DYLD_BOOL NSIsSymbolNameDefinedInImage(
	const struct mach_header *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 mach_header *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 DYLD_BOOL NSAddLibrary(
	const char *pathName);

extern enum DYLD_BOOL NSAddLibraryWithSearching(
	const char *pathName);

extern const struct mach_header * NSAddImage(
	const char *image_name,
	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);

FUTURE SYNOPSIS

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 is an executable or a plugin is composed of one module containing a collection of symbols. A dynamic shared library is composed of one or more modules with each of those modules containing a separate collection of symbols. If a symbol is used from a module then all the symbols 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 and returns the module handle for it. Currently the implementation is limited to only Mach-O MH_BUNDLE types which are used for plugins. A module name is specified when a module is linked so that later NSNameOfModule can be used with the module handle and to do things like report errors. If you want gdb(1) to be able to debug your module, when calling 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:

NSLINKMODULE_OPTION_NONE
    This specifies no options. With this the global symbols from the module are made part of the global symbol table of the program. If any errors occur the handlers installed with NSInstallLinkEditErrorHandlers are called or the default action is taken if there are no handlers.

NSLINKMODULE_OPTION_BINDNOW
    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.

NSLINKMODULE_OPTION_PRIVATE
    With this option the global symbols from the module are not made part of the global symbol table of the program. The global symbols of the module can then be looked up using NSLookupSymbolInModule.

NSLINKMODULE_OPTION_RETURN_ON_ERROR
    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.

NSLINKMODULE_OPTION_DONT_CALL_MOD_INIT_ROUTINES
    With this option the module init routines are not called. This is only useful to the fix-and-continue implementation.

NSLINKMODULE_OPTION_TRAILING_PHYS_NAME
    With this option the parameter, moduleName is assumed to be a string with the logical name of the image with the physical name of the object file tailing after the NULL character of the logical 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:

NSUNLINKMODULE_OPTION_NONE
    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 NSInstallLinkEditErrorHandlers are called or the default action is taken if there are no handlers.

NSUNLINKMODULE_OPTION_KEEP_MEMORY_MAPPED
    With this option the memory for the module is not deallocated allowing pointers into the module to still be valid.

NSUNLINKMODULE_OPTION_RESET_LAZY_REFERENCES
    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' symbols 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 mach_header of a mach_header structure of a dynamic library being used by the program and a symbol name. This returns TRUE or FALSE based on if the symbol is 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) -force_flat_namespace flag or executed with the environment variable DYLD_FORCE_FLAT_NAMESPACE set and the pointer to a mach_header structure is not of a bundle loaded with the NSLINKMODULE_OPTION_PRIVATE option of NSLinkModule(3) then the pointer to a mach_header is ignored and the symbol is looked up in all the images using the first definition if found.

The image handle parameter for NSLookupSymbolInImage and NSIsSymbolNameDefinedInImage 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 a link editor defined symbol as in <mach-o/ldsym.h> and described on the ld(1) man page. Also the dyld(3) routine _dyld_get_image_header(3) and the mach_header pointer arguments to the call back routines called from _dyld_register_func_for_add_image(3) routines can also be used.

NSLookupAndBindSymbol is passed a global symbol name and looks up and binds the symbol into the program. It returns an NSSymbol for the symbol. If any errors occur the handlers installed with NSInstallLinkEditErrorHandlers 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 mach_header 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 image or the image's sub-frameworks or sub-umbrellas. If the program was built with the ld(1) -force_flat_namespace flag or executed with the environment variable DYLD_FORCE_FLAT_NAMESPACE set and the pointer to a mach_header structure is not of a bundle loaded with the NSLINKMODULE_OPTION_PRIVATE option of NSLinkModule(3) then the pointer to a mach_header is ignored and the symbol is looked up in all the images using the first definition found. If the option NSLOOKUPSYMBOLINIMAGE_OPTION_RETURN_ON_ERROR is not used if any errors occur the handlers installed with NSInstallLinkEditErrorHandlers are called or the default action is taken if there are no handlers. The options of NSLookupSymbolInImage are as follows:

NSLOOKUPSYMBOLINIMAGE_OPTION_BIND
    Just bind the non-lazy symbols of module that defines the symbolName and let all lazy symbols in the module be bound on first call. This should be used in the normal case for a trusted module expected to bind without any errors like a module in a system supplied library.

NSLOOKUPSYMBOLINIMAGE_OPTION_BIND_NOW
    Bind 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 against only system supplied libraries which are expected to bind without any errors.

NSLOOKUPSYMBOLINIMAGE_OPTION_BIND_FULLY
    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.

NSLOOKUPSYMBOLINIMAGE_OPTION_RETURN_ON_ERROR
    With this option if errors occur while binding the module that defines the symbolName then the module is automaticly unloaded and NULL is returned as the NSSymbol. To get the error information 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 symbol.

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 mach_header 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 image_name 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 with all the needed dependent libraries are loaded. With the options parameter NSADDIMAGE_OPTION_NONE 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:

NSADDIMAGE_OPTION_RETURN_ON_ERROR
    With this option if errors occur while loading this library it is automatically unloaded and NULL is returned. To get the error information for the library 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.

NSADDIMAGE_OPTION_WITH_SEARCHING
    With this option the image_name 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.

NSADDIMAGE_OPTION_RETURN_ONLY_IF_LOADED
    With this option if the image_name passed for the library has not already been loaded it is not loaded. Only if it has been loaded the pointer to the mach_header will not be NULL.

NSADDIMAGE_OPTION_MATCH_FILENAME_BY_INSTALLNAME
    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 current_version number of the library the program 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 current_version number of the library the 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 provided buffer. If the buffer is not large enough, -1 is returned and the expected buffer size is copied in *bufsize. Note that _NSGetExecutablePath 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.

ERROR HANDLING

NSInstallLinkEditErrorHandlers is passed a pointer to a NSLinkEditErrorHandlers which contains three function pointers to be used for handling 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 runtime loading operation to resolve the undefined reference) the handler simply 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 runtime loading functions as only one set of linking operations can be performed 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 are updated are those that the compiler system generated as indirect references. 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 parameter will be an errno value (see intro(2)). For the error class NSLinkEditMachResourceError the errorNumber parameter will be a kern_return_t 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

ALSO SEE
NSObjectFileImage(3), dyld(3)