ld-classic(1) General Commands Manual ld-classic(1)

ld-classic — linker

ld-classic files... [options] [-o outputfile]

The ld-classic command combines several object files and libraries, resolves references, and produces an output file. ld-classic can produce a final linked image (executable, dylib, or bundle), or with the -r option, produce another object file. If the -o option is not used, the output file produced is named "a.out".

The linker accepts universal (multiple-architecture) input files, but always creates a "thin" (single-architecture), standard Mach-O output file. The architecture for the output file is specified using the -arch option. If this option is not used, ld-classic attempts to determine the output architecture by examining the object files in command line order. The first "thin" architecture determines that of the output file. If no input object file is a "thin" file, the native 32-bit architecture for the host is used.

Usually, ld-classic is not used directly. Instead the compiler driver invokes ld-classic. The compiler driver can be passed multiple -arch options and it will create a universal final linked image by invoking ld-classic multiple times and then running lipo(1) merge the outputs into a universal file.

The object files are loaded in the order in which they are specified on the command line. The segments and the sections in those segments will appear in the output file in the order they are encountered in the object files being linked. All zero fill sections will appear after all non-zero fill sections in their segments.

A static library (aka static archive) is a collection of .o files with a table of contents that lists the global symbols in the .o files. ld-classic will only pull .o files out of a static library if needed to resolve some symbol reference. Unlike traditional linkers, ld-classic will continually search a static library while linking. There is no need to specify a static library multiple times on the command line.

A dynamic library (aka dylib or framework) is a final linked image. Putting a dynamic library on the command line causes two things: 1) The generated final linked image will have encoded that it depends on that dynamic library. 2) Exported symbols from the dynamic library are used to resolve references.

Both dynamic and static libraries are searched as they appear on the command line.

ld-classic maintains a list of directories to search for a library or framework to use. The default library search path is /usr/lib then /usr/local/lib. The -L option will add a new library search path. The default framework search path is /Library/Frameworks then /System/Library/Frameworks. (Note: previously, /Network/Library/Frameworks was at the end of the default path. If you need that functionality, you need to explicitly add -F/Network/Library/Frameworks). The -F option will add a new framework search path. The -Z option will remove the standard search paths. The -syslibroot option will prepend a prefix to all search paths.

By default all references resolved to a dynamic library record the library to which they were resolved. At runtime, dyld uses that information to directly resolve symbols. The alternative is to use the -flat_namespace option. With flat namespace, the library is not recorded. At runtime, dyld will search each dynamic library in load order when resolving symbols. This is slower, but more like how other operating systems resolve symbols.

If the command line specifies to link against dylib A, and when dylib A was built it linked against dylib B, then B is considered an indirect dylib. When linking for two-level namespace, ld does not look at indirect dylibs, except when re-exported by a direct dylibs. On the other hand when linking for flat namespace, ld does load all indirect dylibs and uses them to resolve references. Even though indirect dylibs are specified via a full path, ld-classic first uses the specified search paths to locate each indirect dylib. If one cannot be found using the search paths, the full path is used.

When linking for two-level namespace, ld-classic does not verify that undefines in dylibs actually exist. But when linking for flat namespace, ld-classic does check that all undefines from all loaded dylibs have a matching definition. This is sometimes used to force selected functions to be loaded from a static library.

The default. Produce a mach-o main executable that has file type MH_EXECUTE.
Produce a mach-o shared library that has file type MH_DYLIB.
Produce a mach-o bundle that has file type MH_BUNDLE.
Merges object files to produce another mach-o object file with file type MH_OBJECT.
Produce a mach-o dylinker that has file type MH_DYLINKER. Only used when building dyld.
The default. Implied by -dylib, -bundle, or -execute
Produces a mach-o file that does not use the dyld. Only used building the kernel.
Produces a mach-o file in which the mach_header, load commands, and symbol table are not in any segment. This output type is used for firmware or embedded development where the segments are copied out of the mach-o into ROM/Flash.
arch_name
Specifies which architecture (e.g. ppc, ppc64, i386, x86_64) the output file should be.
path
Specifies the name and location of the output file. If not specified, `a.out' is used.

x
This option tells the linker to search for libx.dylib or libx.a in the library search path. If string x is of the form y.o, then that file is searched for in the same places, but without prepending `lib' or appending `.a' or `.dylib' to the filename.
x
This is the same as the -lx but means to really link with the dylib even if no symbols are used from it. Thus, it can be used suppress warnings about unused dylibs.
x
This is the same as the -lx but specifies that the all symbols in library x should be available to clients linking to the library being created. This was previously done with a separate -sub_library option.
x
This is the same as the -lx but specifies that the dylib is an upward dependency.
x
This is the same as the -lx for locating a static library, but treats all global symbols from the static library as if they are visibility hidden. Useful when building a dynamic library that uses a static library but does not want to export anything from that static library.
x
This is the same as the -lx but forces the library and all references to it to be marked as weak imports. That is, the library is allowed to be missing at runtime.
path_to_dylib
This is the same as placing path_to_dylib on the link line but means to really link with the dylib even if no symbols are used from it. Thus, it can be used suppress warnings about unused dylibs.
path_to_library
This is the same as listing a file name path to a library on the link line and it specifies that the all symbols in library path should be available to clients linking to the library being created. This was previously done with a separate -sub_library option.
path_to_library
This is the same as listing a file name path to a library on the link line but also marks the dylib as an upward dependency.
path_to_library
This is the same as listing a file name path to a library on the link line except that it forces the library and all references to it to be marked as weak imports.
dir
Add dir to the list of directories in which to search for libraries. Directories specified with -L are searched in the order they appear on the command line and before the default search path. In Xcode4 and later, there can be a space between the -L and directory.
Do not search the standard directories when searching for libraries and frameworks.
rootdir
Prepend rootdir to all search paths when searching for libraries or frameworks.
This is now the default (in Xcode4 tools). When processing -lx the linker now searches each directory in its library search paths for `libx.dylib' then `libx.a' before the moving on to the next path in the library search path.
Changes the searching behavior for libraries. The default is that when processing -lx the linker searches each directory in its library search paths for `libx.dylib' then `libx.a'. This option changes the behavior to first search for a file of the form `libx.dylib' in each directory in the library search path, then a file of the form `libx.a' is searched for in the library search paths. This option restores the search behavior of the linker prior to Xcode4.
name[,suffix]
This option tells the linker to search for `name.framework/name' the framework search path. If the optional suffix is specified the framework is first searched for the name with the suffix and then without (e.g. look for `name.framework/name_suffix' first, if not there try `name.framework/name').
name[,suffix]
This is the same as the -framework name[,suffix] but means to really link with the framework even if no symbols are used from it. Thus, it can be used suppress warnings about unused dylibs.
name[,suffix]
This is the same as the -framework name[,suffix] but forces the framework and all references to it to be marked as weak imports. Note: due to a clang optimizations, if functions are not marked weak, the compiler will optimize out any checks if the function address is NULL.
name[,suffix]
This is the same as the -framework name[,suffix] but also specifies that the all symbols in that framework should be available to clients linking to the library being created. This was previously done with a separate -sub_umbrella option.
name[,suffix]
This is the same as the -framework name[,suffix] but also specifies that the framework is an upward dependency.
dir
Add dir to the list of directories in which to search for frameworks. Directories specified with -F are searched in the order they appear on the command line and before the default search path. In Xcode4 and later, there can be a space between the -F and directory.
Loads all members of static archive libraries.
Loads all members of static archive libraries that implement an Objective-C class or category.
path_to_archive
Loads all members of the specified static archive library. Note: -all_load forces all members of all archives to be loaded. This option allows you to target a specific archive.
path_to_archive
Uses specified static library as usual, but treats all global symbols from the static library to as if they are visibility hidden. Useful when building a dynamic library that uses a static library but does not want to export anything from that static library.
suffix
Search for libraries and frameworks with suffix and then without.

segname sectname file
The section sectname in the segment segname is created from the contents of file file. If there's a section (segname,sectname) from any other input, the linker will append the content from the file to that section.
segname sectname
An empty section named sectname in the segment segname. If any of the inputs contains a section (segname,sectname), that section will be included in the output, and this option will be ignored.
file
The linker will add a N_AST stab symbol to the output file where the string is the path pointed by file and its values is the modification time of the file.
file[,dirname]
Specifies that the linker should link the files listed in file. This is an alternative to listing the files on the command line. The file names are listed one per line separated only by newlines. (Spaces and tabs are assumed to be part of the file name.) If the optional directory name, dirname is specified, it is prepended to each name in the list file.
file
Enables dtrace static probes when producing a final linked image. The file file must be a DTrace script which declares the static probes.

Remove functions and data that are unreachable by the entry point or exported symbols.
file
Alters the order in which functions and data are laid out. For each section in the output file, any symbol in that section that are specified in the order file file is moved to the start of its section and laid out in the same order as in the order file file. Order files are text files with one symbol name per line. Lines starting with a # are comments. A symbol name may be optionally preceded with its object file leaf name and a colon (e.g. foo.o:_foo). This is useful for static functions/data that occur in multiple files. A symbol name may also be optionally preceded with the architecture (e.g. ppc:_foo or ppc:foo.o:_foo). This enables you to have one order file that works for multiple architectures. Literal c-strings may be ordered by by quoting the string (e.g. "Hello, world\n") in the order file.
When the -order_file option is not used, the linker lays out functions in object file order and it moves all initializer routines to the start of the __text section and terminator routines to the end. Use this option to disable the automatic rearrangement of initializers and terminators.
platform min_version sdk_version
This is set to indicate the platform, oldest supported version of that platform that output is to be used on, and the SDK that the output was built against. platform is a numeric value as defined in <mach-o/loader.h>, or it may be one of the following strings:
• macos
 
• ios
 
• tvos
 
• watchos
 
• bridgeos
 
• mac-catalyst
 
• ios-simulator
 
• tvos-simulator
 
• watchos-simulator
 
• driverkit
 
Specifying a newer min or SDK version enables the linker to assume features of that OS or SDK in the output file. The format of min_version and sdk_version is a version number such as 10.13 or 10.14
version
This is set to indicate the oldest macOS version that that the output is to be used on. Specifying a later version enables the linker to assumes features of that OS in the output file. The format of version is a macOS version number such as 10.9 or 10.14
version
This is set to indicate the oldest iOS version that that the output is to be used on. Specifying a later version enables the linker to assumes features of that OS in the output file. The format of version is an iOS version number such as 3.1 or 4.0
address
Specifies the preferred load address for a dylib or bundle. The argument address is a hexadecimal number with an optional leading 0x. By choosing non-overlapping address for all dylibs and bundles that a program loads, launch time can be improved because dyld will not need to "rebase" the image (that is, adjust pointers within the image to work at the loaded address). It is often easier to not use this option, but instead use the rebase(1) tool, and give it a list of dylibs. It will then choose non-overlapping addresses for the list and rebase them all. When building a position independent executable, this option will be ignored. This option is also called -seg1addr for compatibility.
When creating a two-level namespace final linked image, normally the linker will hoist up public dylibs that are implicitly linked to make the two-level namespace encoding more efficient for dyld. For example, Cocoa re-exports AppKit and AppKit re-exports Foundation. If you link with -framework Cocoa and use a symbol from Foundation, the linker will implicitly add a load command to load Foundation and encode the symbol as coming from Foundation. If you use this option, the linker will not add a load command for Foundation and encode the symbol as coming from Cocoa. Then at runtime dyld will have to search Cocoa and AppKit before finding the symbol in Foundation.
By default the linker moves all zero fill sections to the end of the __DATA segment and configures them to use no space on disk. This option suppresses that optimization, so zero-filled data occupies space on disk in a final linked image.
Causes all zero-fill sections in the __DATA segment to be merged into one __zerofill section.
Disables linker creation of branch islands which allows images to be created that are larger than the maximum branch distance. Useful with -preload when code is in multiple sections but all are within the branch range.

name
Sets an internal "install path" (LC_ID_DYLIB) in a dynamic library. Any clients linked against the library will record that path as the way dyld should locate this library. If this option is not specified, then the -o path will be used. This option is also called -dylib_install_name for compatibility.
Specifies that the dylib being built can be dead strip by any client. That is, the dylib has no initialization side effects. So if a client links against the dylib, but never uses any symbol from it, the linker can optimize away the use of the dylib.
number
Specifies the compatibility version number of the library. When a library is loaded by dyld, the compatibility version is checked and if the program's version is greater that the library's version, it is an error. The format of number is X[.Y[.Z]] where X must be a positive non-zero number less than or equal to 65535, and .Y and .Z are optional and if present must be non-negative numbers less than or equal to 255. If the compatibility version number is not specified, it has a value of 0 and no checking is done when the library is used. This option is also called -dylib_compatibility_version for compatibility.
number
Specifies the current version number of the library. The current version of the library can be obtained programmatically by the user of the library so it can determine exactly which version of the library it is using. The format of number is X[.Y[.Z]] where X must be a positive non-zero number less than or equal to 65535, and .Y and .Z are optional and if present must be non-negative numbers less than or equal to 255. If the version number is not specified, it has a value of 0. This option is also called -dylib_current_version for compatibility.

This makes a special kind of main executable that is position independent (PIE). On Mac OS X 10.5 and later, the OS the OS will load a PIE at a random address each time it is executed. You cannot create a PIE from .o files compiled with -mdynamic-no-pic. That means the codegen is less optimal, but the address randomization adds some security. When targeting Mac OS X 10.7 or later PIE is the default for main executables.
Do not make a position independent executable (PIE). This is the default, when targeting 10.6 and earlier.
size
By default the linker creates an unreadable segment starting at address zero named __PAGEZERO. Its existence will cause a bus error if a NULL pointer is dereferenced. The argument size is a hexadecimal number with an optional leading 0x. If size is zero, the linker will not generate a page zero segment. By default on 32-bit architectures the page zero size is 4KB. On 64-bit architectures, the default size is 4GB.
implicit_pagezero
When used on main executables, omits the __PAGEZERO segment, and relies on the loader blocking out low memory.
size
Specifies the maximum stack size for the main thread in a program. Without this option a program has a 8MB stack. The argument size is a hexadecimal number with an optional leading 0x. The size should be a multiple of the architecture's page size (4KB or 16KB).
Marks executable so that all stacks in the task will be given stack execution privilege. This includes pthread stacks. This option is only valid when targeting architectures that support stack execution (i.e. Intel).
Preserves all global symbols in main executables during LTO. Without this option, Link Time Optimization is allowed to inline and remove global functions. This option is used when a main executable may load a plug-in which requires certain symbols from the main executable.

executable
This specifies the executable that will be loading the bundle output file being linked. Undefined symbols from the bundle are checked against the specified executable like it was one of the dynamic libraries the bundle was linked with.

Don't turn private external (aka visibility=hidden) symbols into static symbols, but rather leave them as private external in the resulting object file.
Force definition of common symbols. That is, transform tentative definitions into real definitions.

filename
The specified filename contains a list of global symbol names that will remain as global symbols in the output file. All other global symbols will be treated as if they were marked as __private_extern__ (aka visibility=hidden) and will not be global in the output file. The symbol names listed in filename must be one per line. Leading and trailing white space are not part of the symbol name. Lines starting with # are ignored, as are lines with only white space. Some wildcards (similar to shell file matching) are supported. The * matches zero or more characters. The ? matches one character. [abc] matches one character which must be an 'a', 'b', or 'c'. [a-z] matches any single lower case letter from 'a' to 'z'.
symbol
The specified symbol is added to the list of global symbols names that will remain as global symbols in the output file. This option can be used multiple times. For short lists, this can be more convenient than creating a file and using -exported_symbols_list.
Useful for main executable that don't have plugins and thus need no symbol exports.
file
The specified filename contains a list of global symbol names that will not remain as global symbols in the output file. The symbols will be treated as if they were marked as __private_extern__ (aka visibility=hidden) and will not be global in the output file. The symbol names listed in filename must be one per line. Leading and trailing white space are not part of the symbol name. Lines starting with # are ignored, as are lines with only white space. Some wildcards (similar to shell file matching) are supported. The * matches zero or more characters. The ? matches one character. [abc] matches one character which must be an 'a', 'b', or 'c'. [a-z] matches any single lower case letter from 'a' to 'z'.
symbol
The specified symbol is added to the list of global symbols names that will not remain as global symbols in the output file. This option can be used multiple times. For short lists, this can be more convenient than creating a file and using -unexported_symbols_list.
file
The specified filename contains a list of symbol names that are implemented in a dependent dylib and should be re-exported through the dylib being created.
symbol_name alternate_symbol_name
Create an alias named alternate_symbol_name for the symbol symbol_name. By default the alias symbol has global visibility. This option was previous the -idef:indir option.
filename
The specified filename contains a list of aliases. The symbol name and its alias are on one line, separated by whitespace. Lines starting with # are ignored.
Alters how symbols are resolved at build time and runtime. With -two_levelnamespace (the default), the linker only searches dylibs on the command line for symbols, and records in which dylib they were found. With -flat_namespace, the linker searches all dylibs on the command line and all dylibs those original dylibs depend on. The linker does not record which dylib an external symbol came from, so at runtime dyld again searches all images and uses the first definition it finds. In addition, any undefines in loaded flat_namespace dylibs must be resolvable at build time.
symbol_name
Specified that symbol symbol_name must be defined for the link to succeed. This is useful to force selected functions to be loaded from a static library.
symbol_name
Specified that it is ok for symbol_name to have no definition. With -two_levelnamespace, the resulting symbol will be marked dynamic_lookup which means dyld will search all loaded images.
treatment
Specifies how undefined symbols are to be treated. Options are: error, warning, suppress, or dynamic_lookup. The default is error. Note: dynamic_lookup that depends on lazy binding will not work with chained fixups.
path
Add path to the runpath search path list for image being created. At runtime, dyld uses the runpath when searching for dylibs whose load path begins with @rpath/.
treatment
Specifies how commons (aka tentative definitions) are resolved with respect to dylibs. Options are: ignore_dylibs, use_dylibs, error. The default is ignore_dylibs which means the linker will turn a tentative definition in an object file into a real definition and not even check dylibs for conflicts. The dylibs option means the linker should check linked dylibs for definitions and use them to replace tentative definitions from object files. The error option means the linker should issue an error whenever a tentative definition in an object file conflicts with an external symbol in a linked dylib. See also -warn_commons.

Log why each object file in a static library is loaded. That is, what symbol was needed. Also called -whyload for compatibility.
symbol_name
Logs a chain of references to symbol_name. Only applicable with -dead_strip . It can help debug why something that you think should be dead strip removed is not removed. See -exported_symbols_list for syntax and use of wildcards.
Logs information about the amount of memory and time the linker used.
Logs each file (object, archive, or dylib) the linker loads. Useful for debugging problems with search paths where the wrong library is loaded.
Logs information about the processing of a -order_file.
map_file_path
Writes a map file to the specified path which details all symbols and their addresses in the output image.

Do not put debug information (STABS or DWARF) in the output file.
Do not put non-global symbols in the output file's symbol table. Non-global symbols are useful when debugging and getting symbol names in back traces, but are not used at runtime. If -x is used with -r non-global symbol names are not removed, but instead replaced with a unique, dummy name that will be automatically removed when linked into a final linked image. This allows dead code stripping, which uses symbols to break up code and data, to work properly and provides the security of having source symbol names removed.
filename
The specified filename contains a list of non-global symbol names that should be removed from the output file's symbol table. All other non-global symbol names will remain in the output files symbol table. See -exported_symbols_list for syntax and use of wildcards.
filename
The specified filename contains a list of non-global symbol names that should be remain in the output file's symbol table. All other symbol names will be removed from the output file's symbol table. See -exported_symbols_list for syntax and use of wildcards.
prefix-path
When generating the debug map, the linker will remove the specified prefix-path from the path in OSO symbols. This can be used so to help build servers generate identical binaries. If '.' is passed as argument, the linker will expand the argument to the current working directory.

Generates an embedded bitcode bundle in the output binary. The bitcode bundle is embedded in __LLVM, __bundle section. This option requires all the object files, static libraries and user frameworks/dylibs contain bitcode. Note: not all the linker options are supported to use together with -bitcode_bundle.
Specifies this option together with -bitcode_bundle to hide all non-exported symbols from output bitcode bundle. The hide symbol process might not be reversible. To obtain a reverse mapping file to recover all the symbols, use -bitcode_symbol_map option.
path
Specifies the output for bitcode symbol reverse mapping (.bcsymbolmap). If path is an existing directory, UUID.bcsymbolmap will be written to that directory. Otherwise, the reverse map will be written to a file at path.

@response_file_path
Inserts contents of file at response_file_path into arguments. This allows for linker command line args to be store in a file. Note: ld is normally invoked through clang, and clang also interprets @file on the command line. To have clang ignore the @file and pass it through to ld, use -Wl,@file.
Prints the version of the linker.
Directs the linker to add an ad-hoc codesignature to the output file. The default for Apple Silicon binaries is to be ad-hoc codesigned.
Directs the linker to not add ad-hoc codesignature to the output file, even for Apple Silicon binaries.
By default the linker moves some data sections into __DATA_CONST if it knows the target OS version supports that. This option option overrides the default behavior and forces the use of __DATA_CONST.
By default the linker moves some data sections into __DATA_CONST if it knows the target OS version supports that. This option option overrides the default behavior and forces the linker to never move sections to __DATA_CONST.
By default the linker moves __objc_selrefs section into __DATA_CONST if it knows the target OS version supports that. This option option overrides the default behavior and forces __objc_selrefs being in __DATA_CONST. Note this only applies if the __DATA_CONST segment is enabled. See -data_const for more information.
By default the linker moves __objc_selrefs section into __DATA_CONST if it knows the target OS version supports that. This option option overrides the default behavior and keeps the __objc_selrefs section in __DATA.
Prints the version info about the linker in JSON
Error if any symbols are weak imports (i.e. allowed to be unresolved (NULL) at runtime). Useful for config based projects that assume they are built and run on the same OS version.
Don't run deduplication pass in linker
Prints names of functions that are eliminated by deduplication and total code savings size.
Error if the output contains any static initializers
Do not warn if the output contains any static initializers
Do not warn about issues that are only problems for binaries shipping to customers.
treatment
Specifies how unaligned pointers in __DATA segments should be handled. Options are: 'warning', 'error', or 'suppress'. The default for arm64e is 'error' and for all other architectures it is 'suppress'.
filename
Specifies a file containing the names of data symbols likely to be dirtied. If the linker is creating a __DATA_DIRTY segment, those symbols will be moved to that segment.
value
Any common symbols (aka tentative definitions, or uninitialized (zeroed) variables) that have no explicit alignment are normally aligned to their next power of two size (e.g. a 240 byte array is 256 aligned). This option lets you reduce the max alignment. For instance, a value of 0x40 would reduce the alignment for a 240 byte array to 64 bytes (instead of 256). The value specified must be a hexadecimal power of two If -max_default_common_align is not used, the default alignment is already limited to 0x8 (2^3) bytes for -preload and 0x8000 (2^15) for all other output types.
segment_name filename
Moves data symbols to another segment. The command line option specifies the target segment name and a path to a file containing a list of symbols to move. Comments can be added to the symbol file by starting a line with a #. If there are multiple instances of a symbol name (for instance a "static int foo=5;" in multiple files) the symbol name in the symbol list file can be prefixed with the object file name (e.g. "init.o:_foo") to move a specific instance.
segment_name filename
Moves code symbols to another segment. The command line option specifies the target segment name and a path to a file containing a list of symbols to move. Comments can be added to the symbol file by starting a line with a #. If there are multiple instances of a symbol name (for instance a "static int foo() {}" in multiple files) the symbol name in the symbol list file can be prefixed with the object file name (e.g. "init.o:_foo") to move a specific instance.
orgSegment orgSection newSegment newSection
Renames section orgSegment/orgSection to newSegment/newSection.
orgSegment newSegment
Renames all sections with orgSegment segment name to have newSegment segment name.
For using in debugging -rename_section, -rename_segment, -move_to_ro_segment, and -move_to_rw_segment. This option prints out a line show where and why each symbol was moved. Note: These options do chain. For each symbol, the linker first checks -move_to_ro_segment and -move_to_rw_segment. Next it applies any -rename_section options, and lastly and -rename_segment options.
segname colon_separated_section_list
Only for use with -preload. Specifies the order that sections with the specified segment should be layout out. For example: "-section_order __ROM __text:__const:__cstring".
colon_separated_segment_list
Only for use with -preload. Specifies the order segments should be layout out. For example: "-segment_order __ROM:__ROM2:__RAM".
Normally i386 main executables will be marked so that the Mac OS X 10.7 and later kernel will only allow pages with the x-bit to execute instructions. This option overrides that behavior and allows instructions on any page to be executed.
Specifies that the code is being linked for use in an application extension. The linker will then validate that any dynamic libraries linked against are safe for use in application extensions.
Specifies that the code is being linked is not safe for use in an application extension. For instance, can be used when creating a framework that should not be used in an application extension.
Causes the linker to exit with a non-zero value if any warnings were emitted.
Normally in -r mode, the linker produces .eh labels on all FDEs in the __eh_frame section. This option suppresses those labels. Those labels are not needed by the Mac OS X 10.6 linker but are needed by earlier linker tools.
When producing a final linked image, the linker processes the __eh_frame section and produces an __unwind_info section. Most FDE entries in the __eh_frame can be represented by a 32-bit value in the __unwind_info section. The option issues a warning for any function whose FDE cannot be expressed in the compact unwind format.
Issue a warning if the resulting final linked image contains weak external symbols. Such symbols require dyld to do extra work at launch time to coalesce those symbols.
Issue an erro if the resulting final linked image contains weak external symbols. Such symbols require dyld to do extra work at launch time to coalesce those symbols.
Warn about dylibs that are linked by no symbols are used from them.
Don't warn about dylibs that are linked by no symbols are used from them.
Remove dylibs that are unreachable by the entry point or exported symbols. That is, suppresses the generation of load command commands for dylibs which supplied no symbols during the link. This option should not be used when linking against a dylib which is required at runtime for some indirect reason such as the dylib has an important initializer.
Normally the linker considers different cpu-subtype for ARM (e.g. armv4t and armv6) to be different different architectures that cannot be mixed at build time. This option relaxes that requirement, allowing you to mix object files compiled for different ARM subtypes.
Do not generate an LC_UUID load command in the output file. Be warned that binaries without UUIDs may cause the debugger and crash reporting tools to be unable to track and inspect the binary.
Generate a random LC_UUID load command in the output file. By default the linker generates the UUID of the output file based on a hash of the output file's content. But for very large output files, the hash can slow down the link. Using a hash based UUID is important for reproducible builds, but if you are just doing rapid debug builds, using -random_uuid may improve turn around time.
Sets the MH_ROOT_SAFE bit in the mach header of the output file.
Sets the MH_SETUID_SAFE bit in the mach header of the output file.
Indirects access to all to exported symbols when creating a dynamic library.
symbol_name
The specified symbol_name will be run as the first initializer. Only used when creating a dynamic library.
library_name
The specified dylib will be re-exported. For example the library_name for /usr/lib/libobjc_profile.A.dylib would be libobjc. Only used when creating a dynamic library.
framework_name
The specified framework will be re-exported. Only used when creating a dynamic library.
name
Restricts what can link against the dynamic library being created. By default any code can link against any dylib. But if a dylib is supposed to be private to a small set of clients, you can formalize that by adding a -allowable_client for each client. If a client is libfoo.1.dylib its -allowable_client name would be "foo". If a client is Foo.framework its -allowable_client name would be "Foo". For the degenerate case where you want no one to ever link against a dylib, you can set the -allowable_client to "!".
name
Enables a bundle to link against a dylib that was built with -allowable_client. The name specified must match one of the -allowable_client names specified when the dylib was created.
framework_name
Specifies that the dylib being linked is re-exported through an umbrella framework of the specified name.
size
Specifies the minimum space for future expansion of the load commands. Only useful if intend to run install_name_tool to alter the load commands later. Size is a hexadecimal number.
Automatically adds space for future expansion of load commands such that all paths could expand to MAXPATHLEN. Only useful if intend to run install_name_tool to alter the load commands later.
Sets a bit in the mach header of the resulting binary which tells dyld to bind all symbols when the binary is loaded, rather than lazily.
Sets a bit in the mach header of the resulting binary which tells dyld to not only use flat namespace for the binary, but force flat namespace binding on all dylibs and bundles loaded in the process. Can only be used when linking main executables.
segname sectname value
The section named sectname in the segment segname will have its alignment set to value, where value is a hexadecimal number that must be an integral power of 2.
address
Specifies the initial address of the stack pointer value, where value is a hexadecimal number rounded to a page boundary.
segname max_prot init_prot
Specifies the maximum and initial virtual memory protection of the named segment, name, to be max and init ,respectively. The values for max and init are any combination of the characters `r' (for read), `w' (for write), `x' (for execute) and `-' (no access).
filename
Specifies a file containing base addresses for dynamic libraries. Each line of the file is a hexadecimal base address followed by whitespace then the install name of the corresponding dylib. The # character denotes a comment.
address
Allows a dynamic library to be built where the read-only and read-write segments are not contiguous. The address specified is a hexadecimal number that indicates the base address for the read-write segments.
address
Allows a dynamic library to be built where the read-only and read-write segments are not contiguous. The address specified is a hexadecimal number that indicates the base address for the read-only segments.
name address
Specifies the starting address of the segment named name to be address. The address must be a hexadecimal number that is a multiple of 4K page size.
name size
Specifies the page size used by the specified segment. By default the page size is 4096 for all segments. The linker will lay out segments such that size of a segment is always an even multiple of its page size.
install_name:file_name
Specifies that a dynamic shared library is in a different location than its standard location. Use this option when you link with a library that is dependent on a dynamic library, and the dynamic library is in a location other than its default location. install_name specifies the path where the library normally resides. file_name specifies the path of the library you want to use instead. For example, if you link to a library that depends upon the dynamic library libsys and you have libsys installed in a nondefault location, you would use this option: -dylib_file /lib/libsys_s.A.dylib:/me/lib/libsys_s.A.dylib.
The created output file will be in the prebound format. This was used in Mac OS X 10.3 and earlier to improve launch performance.
treatment
Specifies what to do if a symbol is weak-imported in one object file but not weak-imported in another. The valid treatments are: error, weak, or non-weak. The default is non-weak.
treatment
Enables the use of relocations which will cause dyld to modify (copy-on-write) read-only pages. The compiler will normally never generate such code.
The is only applicable with -arch ppc. It tells the linker to ignore the PowerPC cpu requirements (e.g. G3, G4 or G5) encoded in the object files and mark the resulting binary as runnable on any PowerPC cpu.
path
Only used when building dyld.
Suppresses warning messages about files that have the wrong architecture for the -arch flag
Turns into errors, warnings about files that have the wrong architecture for the -arch flag.
symbol_name
Specifies the entry point of a main executable. By default the entry name is "start" which is found in crt1.o which contains the glue code need to set up and call main().
Suppress all warning messages
name
Specifies the install name of a dylib if -install_name is not used. This option is used by compiler driver when it is invoked with multiple -arch arguments.
Specifies that the linker should augment error and warning messages with the architecture name. This option is used by compiler driver when it is invoked with multiple -arch arguments.
Specifies that hints should be added to the resulting binary that can help speed up runtime binding by dyld as long as the libraries being linked against have not changed.
path
Create a file at the specified path containing a graph of symbol dependencies. The .dot file can be viewed in GraphViz.
Add section based relocation records to a final linked image. These relocations are ignored at runtime by dyld.
Print a warning when the linker cannot do a BINCL/EINCL optimization because the compiler put a bad stab symbol inside a BINCL/EINCL range.
Print a warning whenever a tentative definition in an object file is found and a external symbol by the same name is also found in a linked dylib. This often means that the extern keyword is missing from a variable declaration in a header file.
[i386 only] Makes the __IMPORT segment of a final linked images read-only. This option makes a program slightly more secure in that the JMP instructions in the i386 fast stubs cannot be easily overwritten by malicious code. The downside is the dyld must use mprotect() to temporarily make the segment writable while it is binding the stubs.
[i386 only] Instead of using single JMP instruction stubs, the linker creates code in the __TEXT segment which calls through a lazy pointer in the __DATA segment.
filename
The specified filename contains a list of global symbol names that should always be accessed indirectly. For instance, if libSystem.dylib is linked such that _malloc is interposable, then calls to malloc() from within libSystem will go through a dyld stub and could potentially indirected to an alternate malloc. If libSystem.dylib were built without making _malloc interposable then if _malloc was interposed at runtime, calls to malloc from with libSystem would be missed (not interposed) because they would be direct calls.
By default the linker creates a compress table of function start addresses in the LINKEDIT of final linked image. This option disables that behavior.
By default when producing final linked image, the linker will optimize Objective-C classes by merging any categories on a class into the class. Both the class and its categories must be defined in the image being linked for the optimization to occur. Using this option disables that behavior.
By default when producing final linked image, if targeting a new enough OS version, the linker will rewrite ObjC method lists from the tradition three pointers to use three read-only delta pointers. This option allows you to force the use of relative method lists even though the OS version is too low.
By default when producing final linked image, if targeting a new enough OS version, the linker will rewrite ObjC method lists from the tradition three pointers to use three read-only delta pointers. This option allows you to force the use of traditional three pointer method lists.
filename
When performing Link Time Optimization (LTO) and a temporary mach-o object file is needed, if this option is used, the temporary file will be stored at the specified path and remain after the link is complete. Without the option, the linker picks a path and deletes the object file before the linker tool completes, thus tools such as the debugger or dsymutil will not be able to access the DWARF debug info in the temporary object file.
path
When performing Link Time Optimization (LTO), the linker normally loads libLTO.dylib relative to the linker binary (../lib/libLTO.dylib). This option allows the user to specify the path to a specific libLTO.dylib to load instead.
path
When performing Incremental Link Time Optimization (LTO), use this directory as a cache for incremental rebuild.
seconds
When performing Incremental Link Time Optimization (LTO), the cache will pruned after the specified interval. A value 0 will force pruning to occur and a value of -1 will disable pruning.
seconds
When pruning the cache for Incremental Link Time Optimization (LTO), the cache entries are removed after the specified interval.
percent
When performing Incremental Link Time Optimization (LTO), the cache will be pruned to not go over this percentage of the free space. I.e. a value of 100 would indicate that the cache may fill the disk, and a value of 50 would indicate that the cache size will be kept under the free disk space.
For use with -static or -preload when -pie is used. Tells the linker to add a __TEXT,__chain_starts section which starts with a dyld_chained_starts_offsets struct which specifies the pointer format and the offsets to the start of every fixup chain.
Same as -fixup_chains_section but fixes a bug. The offsets in the __chain_starts section are vm-offsets from the __TEXT segment, and the rebase targets in the chains are vm-offsets.
For arm64e only. For use with -static or -preload when -pie is used. Tells the linker to add a __TEXT,__thread_starts section which starts with a 32-bit flag field, followed by an array 32-bit values. Each value is the offset to the start of a fixup chain. This option is deprecated.
During development, this option can be used to space out all global variables so each is on a separate page. This is useful when analyzing dirty and resident pages. The information can then be used to create an order file to cluster commonly used/dirty globals onto the same page(s).
Normally, the linker will add extra info to dylibs with -install_name starting with /usr/lib or /System/Library/ that allows the dylib to be placed into the dyld shared cache. Adding this option tells the linker to not add that extra info.
For use when linking against versioned frameworks that do not have a normal variant. By default when -framework Foo,_suffix is used, the linker will follow Foo.framework/Foo if it is a symbolic link, append _suffix and search for a file with that path. When this option is used, the linker will also search for Foo.framework/Versions/Current/Foo_suffix.
Override the choice of linker, and force the use of ld-classic to link the binary. This is incompatible with options such as -merge*, used to build/merge libraries.

value
All segments must be page aligned.
Object files (MH_OBJECT) with a LINKEDIT segment are no longer supported. This option is obsolete.
This is the default. This option is obsolete.
Fixed VM shared libraries (MH_FVMLIB) are no longer supported. This option is obsolete.
segname sectname
Adding a local label at a section start is no longer supported. This option is obsolete.
The MH_NOFIXPREBINDING bit of mach_headers has been ignored since Mac OS X 10.3.9. This option is obsolete.
Multi-modules in dynamic libraries have been ignored at runtime since Mac OS X 10.4.0. This option is obsolete.
Multi-modules in dynamic libraries have been ignored at runtime since Mac OS X 10.4.0. This option is obsolete.
When using -prebind, the linker allows overlapping by default, so this option is obsolete.
LD_PREBIND is no longer supported as a way to force on prebinding, so there no longer needs to be a command line way to override LD_PREBIND. This option is obsolete.
treatment
This option was an attempt to warn about linking .o files compiled without -mdynamic-no-pic into a main executable, but the false positive rate generated too much noise to make the option useful. This option is obsolete.
This option was removed in Mac OS X 10.2.
This is now the default so does not need to be specified.
Multi-modules in dynamic libraries have been ignored at runtime since Mac OS X 10.4.0. This option is obsolete.
The linker never dead strips initialization and termination routines. They are considered "roots" of the dead strip graph.
basefile
Obsolete incremental load format. This option is obsolete.
Used with -A option to strip base file's symbols. This option is obsolete. Obsolete option to produce a load map. Use -map option instead.
Don't strip any symbols. This is the default. This option is obsolete.
Optimize stabs debug symbols to remove duplicates. This is the default. This option is obsolete.
Write minimal stabs which causes the debugger to open and read the original .o file for full stabs. This style of debugging is obsolete in Mac OS X 10.5. This option is obsolete.
Strip local symbols that begin with 'L'. This is the default. This option is obsolete.
Completely strip the output, including removing the symbol table. This file format variant is no longer supported. This option is obsolete.
Don't treat multiple definitions as an error. This is no longer supported. This option is obsolete.
symbol
Display each file in which symbol is used. This was previously used to debug where an undefined symbol was used, but the linker now automatically prints out all usages. The -why_live option can also be used to display what kept a symbol from being dead striped. This option is obsolete.
number
Used to control how many occurrences of each symbol specified with -y would be shown. This option is obsolete.
Only used when linking an umbrella framework. Sets the MH_NOMULTIDEFS bit in the mach_header. The MH_NOMULTIDEFS bit has been obsolete since Mac OS X 10.4. This option is obsolete.
treatment
Previously provided a way to warn or error if any of the symbol definitions in the output file matched any definitions in dynamic library being linked. This option is obsolete.
treatment
Previously provided a way to warn or error if any of the symbols used from a dynamic library were also available in another linked dynamic library. This option is obsolete.
Previously prevented errors when -flat_namespace, -bundle, and -bundle_loader were used and the bundle contained a definition that conflicted with a symbol in the main executable. The linker no longer errors on such conflicts. This option is obsolete.
This is the default. This option is obsolete.
path
Use path instead of the install name of the library for matching an entry in the seg_addr_table. This option is obsolete.
segname sectname orderfile
Replaced by more general -order_file option.
Produced extra logging about which entries from a sectorder entries were used. Replaced by -order_file_statistics. This option is obsolete.
name[,suffix]
This is the same as the -framework name[,suffix] except that the linker will construct glue code so that the framework is not loaded until the first function in it is called. You cannot directly access data or Objective-C classes in a framework linked this way. This option is deprecated.
x
This is the same as the -lx but it is only for shared libraries and the linker will construct glue code so that the shared library is not loaded until the first function in it is called. This option is deprecated.
path_to_library
This is the same as listing a file name path to a shared library on the link line except that the linker will construct glue code so that the shared library is not loaded until the first function in it is called. This option is deprecated.

ld(1), as(1), ar(1), cc(1), dyld_info(1), nm(1), otool(1) lipo(1), arch(3), dyld(3), Mach-O(5), strip(1), rebase(1)

September 10, 2020 Darwin