NSModule(3) Library Functions Manual 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);
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 col-
lection 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. 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.
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 pro-
gram 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 defi-
nition 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 imple-
mented 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 NSLOOKUPSYMBOLINIM-
AGE_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 vari-
ables 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 NSAddIm-
age() 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 pro-
gram 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 _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.
ERROR HANDLING
NSInstallLinkEditErrorHandlers is passed a pointer to a NSLinkEditErrorHandlers 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 runtime loading 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 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 link-
ing process has completed (for example later unlink the module). The dynamic link editor updates the references to the symbol if the han-
dler 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 warn-
ings 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 error-
Number 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 file-
name parameter will be
ALSO SEE
NSObjectFileImage(3), dyld(3)
Apple Computer, Inc. March 10, 2001 NSModule(3)