.Dd Aug 7, 2012 .Os .Dt DLOPEN 3 .Sh NAME .Nm dlopen .Nd load and link a dynamic library or bundle .Sh SYNOPSIS .In dlfcn.h .Ft void* .Fn dlopen "const char* path" "int mode" .Sh DESCRIPTION .Fn dlopen examines the mach-o file specified by .Fa path . If the file is compatible with the current process and has not already been loaded into the current process, it is loaded and linked. After being linked, if it contains any initializer functions, they are called, before .Fn dlopen returns. .Fn dlopen can load dynamic libraries and bundles. It returns a handle that can be used with .Fn dlsym and .Fn dlclose . A second call to .Fn dlopen with the same path will return the same handle, but the internal reference count for the handle will be incremented. Therefore all .Fn dlopen calls should be balanced with a .Fn dlclose call. .Pp If a null pointer is passed in .Fa path , .Fn dlopen returns a handle equivalent to RTLD_DEFAULT. .Pp .Fa mode contains options to .Fn dlopen . It must contain one or more of the following values, possibly ORed together: .Pp .Bl -tag -width RTLD_LAZYX .It Dv RTLD_LAZY Each external function reference is bound the first time the function is called. .It Dv RTLD_NOW All external function references are bound immediately during the call to .Fn dlopen . .El .Pp .Dv RTLD_LAZY is normally preferred, for reasons of efficiency. However, .Dv RTLD_NOW is useful to ensure that any undefined symbols are discovered during the call to .Fn dlopen . If neither RTLD_LAZY nor RTLD_NOW is specified, the default is RTLD_LAZY. .Pp One of the following flags may be ORed into the .Fa mode argument: .Bl -tag -width RTLD_LOCALX .It Dv RTLD_GLOBAL Symbols exported from this image (dynamic library or bundle) will be available to any images build with -flat_namespace option to .Xr ld 1 or to calls to .Fn dlsym when using a special handle. .It Dv RTLD_LOCAL Symbols exported from this image (dynamic library or bundle) are generally hidden and only availble to .Fn dlsym when directly using the handle returned by this call to .Fn dlopen . .Pp .El If neither RTLD_GLOBAL nor RTLD_LOCAL is specified, the default is RTLD_GLOBAL. .Pp One of the following may be ORed into the .Fa mode argument: .Bl -tag -width RTLD_NODELETEX .It Dv RTLD_NOLOAD The specified image is not loaded. However, a valid .Fa handle is returned if the image already exists in the process. This provides a way to query if an image is already loaded. The .Fa handle returned is ref-counted, so you eventually need a corresponding call to .Fn dlclose .It Dv RTLD_NODELETE The specified image is tagged so that will never be removed from the address space, even after all clients have released it via .Fn dlclose .El .Pp Additionally, the following may be ORed into the .Fa mode argument: .Bl -tag -width RTLD_FIRSTX .It Dv RTLD_FIRST The retuned .Fa handle is tagged so that any .Fn dlsym calls on the .Fa handle will only search the image specified, and not subsequent images. If .Fa path is NULL and the option RTLD_FIRST is used, the .Fa handle returned will only search the main executable. .El .Sh SEARCHING .Fn dlopen searches for a compatible Mach-O file in the directories specified by a set of environment variables and the process's current working directory. When set, the environment variables contain a colon-separated list of directory paths, which can be absolute or relative to the current working directory. .Pp When .Fa path does not contain a slash character (i.e. it is just a leaf name), .Fn dlopen searches the following until it finds a compatible Mach-O file: $LD_LIBRARY_PATH, $DYLD_LIBRARY_PATH, current working directory, $DYLD_FALLBACK_LIBRARY_PATH. .Pp When .Fa path looks like a framework path (e.g. /stuff/foo.framework/foo), .Fn dlopen searches the following until it finds a compatible Mach-O file: $DYLD_FRAMEWORK_PATH (with framework partial path from .Fa path ), then the supplied .Fa path (using current working directory for relative paths), then $DYLD_FALLBACK_FRAMEWORK_PATH (with framework partial path from .Fa path ). .Pp When .Fa path contains a slash but is not a framework path (i.e. a full path or a partial path to a dylib), .Fn dlopen searches the following until it finds a compatible Mach-O file: $DYLD_LIBRARY_PATH (with leaf name from .Fa path ), then the supplied .Fa path (using current working directory for relative paths), then $DYLD_FALLBACK_LIBRARY_PATH (with leaf name from .Fa path ). .Pp Note: If DYLD_FALLBACK_LIBRARY_PATH is not set, dlopen operates as if DYLD_FALLBACK_LIBRARY_PATH was set to $HOME/lib:/usr/local/lib:/usr/lib. .Pp Note: If DYLD_FALLBACK_FRAMEWORK_PATH is not set, dlopen operates as if DYLD_FALLBACK_FRAMEWORK_PATH was set to $HOME/Library/Frameworks:/Library/Frameworks:/Network/Library/Frameworks:/System/Library/Frameworks. .Pp Note: There are no configuration files to control dlopen searching. .Pp Note: If the main executable is a set[ug]id binary or codesigned with entitlements, then all environment variables are ignored, and only a full path can be used. .Pp Note: Mac OS X uses "universal" files to combine 32-bit and 64-bit libraries. This means there are no separate 32-bit and 64-bit search paths. .Pp .Sh RETURN VALUES If .Fn dlopen fails, it returns a null pointer, and sets an error condition which may be interrogated with .Fn dlerror . .Pp .Sh SEE ALSO .Xr dlopen_preflight 3 .Xr dlclose 3 .Xr dlsym 3 .Xr dlerror 3 .Xr dyld 1 .Xr ld 1