--- name: "ld.lld-7" section: "1" platform: "linux" package: "lld-7" version: "1:7.0.1-8+deb10u2" release: "Debian 10 (Buster)" platforms: ["linux"] url: "https://new.carta.tech/ld.lld-7" --- # ld.lld-7(1) ELF linker from the LLVM project ## NAME **ld.lld** – ELF linker from the LLVM project ## SYNOPSIS **ld.lld** \[*options*\] *objfile* *...* ## DESCRIPTION A linker takes one or more object, archive, and library files, and combines them into an output file (an executable, a shared library, or another object file). It relocates code and data from the input files and resolves symbol references between them. **ld.lld** is a drop-in replacement for the GNU BFD and gold linkers. It accepts most of the same command line arguments and linker scripts as GNU linkers. These options are available: - **--allow-multiple-definition** Do not error if a symbol is defined multiple times. The first definition will be used. - **--apply-dynamic-relocs** Apply link-time values for dynamic relocations. - **--as-needed** Only set DT\_NEEDED for shared libraries if used. - **--auxiliary**=*value* Set the DT\_AUXILIARY field to the specified name. - **--Bdynamic**, **--dy** Link against shared libraries. - **--Bstatic**, **--static**, **--dn** Do not link against shared libraries. - **--Bsymbolic** Bind defined symbols locally. - **--Bsymbolic-functions** Bind defined function symbols locally. - **--build-id**=*value* Generate a build ID note. *value* may be one of **fast**, **md5**, **sha1**, **tree**, **uuid**, **0x***hex-string*, and **none**. **tree** is an alias for **sha1**. Build-IDs of type **fast**, **md5**, **sha1**, and **tree** are calculated from the object contents. **fast** is not intended to be cryptographically secure. - **--build-id** Synonym for **--build-id**=**fast**. - **--color-diagnostics**=*value* Use colors in diagnostics. *value* may be one of **always**, **auto**, and **never**. **auto** enables color if and only if output is to a terminal. - **--color-diagnostics** Alias for **--color-diagnostics**=**auto**. - **--compress-debug-sections**=*value* Compress DWARF debug sections. *value* may be **none** or **zlib**. - **--cref** Output cross reference table. - **--define-common**, **-d** Assign space to common symbols. - **--defsym**=*symbol*=*expression* Define a symbol alias. *expression* may be another symbol or a linker script expression. For example, ‘--defsym=foo=bar’ or ‘--defsym=foo=bar+0x100’. - **--demangle** Demangle symbol names. - **--disable-new-dtags** Disable new dynamic tags. - **--discard-all**, **-x** Delete all local symbols. - **--discard-locals**, **-X** Delete temporary local symbols. - **--discard-none** Keep all symbols in the symbol table. - **--dynamic-linker**=*value* Specify the dynamic linker to be used for a dynamically linked executable. This is recorded in an ELF segment of type PT\_INTERP. - **--dynamic-list**=*file* Read a list of dynamic symbols from *file*. - **--eh-frame-hdr** Request creation of .eh\_frame\_hdr section and PT\_GNU\_EH\_FRAME segment header. - **--emit-relocs**, **-q** Generate relocations in the output. - **--enable-new-dtags** Enable new dynamic tags. - **--end-lib** End a grouping of objects that should be treated as if they were together in an archive. - **--entry**=*entry* Name of entry point symbol. - **--error-limit**=*value* Maximum number of errors to emit before stopping. A value of zero indicates that there is no limit. - **--error-unresolved-symbols** Report unresolved symbols as errors. - **--exclude-libs**=*value* Exclude static libraries from automatic export. - **--export-dynamic**, **-E** Put symbols in the dynamic symbol table. - **--export-dynamic-symbol**=*symbol* Include *symbol* in the dynamic symbol table. - **--fatal-warnings** Treat warnings as errors. - **--filter**=*value*, **-F** *value* Set the DT\_FILTER field to the specified value. - **--fini**=*symbol* Specify a finalizer function. - **--format**=*input-format*, **-b** *input-format* Specify the format of the inputs following this option. *input-format* may be one of **binary**, **elf**, and **default**. **default** is a synonym for **elf**. - **--gc-sections** Enable garbage collection of unused sections. - **--gdb-index** Generate .gdb\_index section. - **--hash-style**=*value* Specify hash style. *value* may be **sysv**, **gnu**, or **both**. **both** is the default. - **--help** Print a help message. - **--icf**=**all** Enable identical code folding. - **--icf**=**safe** Enable safe identical code folding. - **--icf**=**none** Disable identical code folding. - **--image-base**=*value* Set the base address to *value*. - **--init**=*symbol* Specify an initializer function. - **--keep-unique**=*symbol* Do not fold *symbol* during ICF. - **-l** *libName,* **--library**=*libName* Root name of library to use. - **-L** *dir*, **--library-path**=*dir* Add a directory to the library search path. - **--lto-aa-pipeline**=*value* AA pipeline to run during LTO. Used in conjunction with **--lto-newpm-passes**. - **--lto-newpm-passes**=*value* Passes to run during LTO. - **--lto-O***opt-level* Optimization level for LTO. - **--lto-partitions**=*value* Number of LTO codegen partitions. - **-m** *value* Set target emulation. - **--Map**=*file*, **-M** *file* Print a link map to *file*. - **--no-as-needed** Always set DT\_NEEDED for shared libraries. - **--no-color-diagnostics** Do not use colors in diagnostics. - **--no-define-common** Do not assign space to common symbols. - **--no-demangle** Do not demangle symbol names. - **--no-dynamic-linker** Inhibit output of an .interp section. - **--no-gc-sections** Disable garbage collection of unused sections. - **--no-gnu-unique** Disable STB\_GNU\_UNIQUE symbol binding. - **--no-rosegment** Do not put read-only non-executable sections in their own segment. - **--no-threads** Do not run the linker multi-threaded. - **--no-undefined-version** Report version scripts that refer undefined symbols. - **--no-undefined** Report unresolved symbols even if the linker is creating a shared library. - **--no-whole-archive** Restores the default behavior of loading archive members. - **--no-pie** Do not create a position independent executable. - **--noinhibit-exec** Retain the executable output file whenever it is still usable. - **--nostdlib** Only search directories specified on the command line. - **-o** *path* Write the output executable, library, or object to *path*. If not specified, a.out is used as a default. - **-O***value* Optimize output file size. *value* may be: - **0** Disable string merging. - **1** Enable string merging. - **2** Enable string tail merging. **-O****1** is the default. - **--oformat**=*format* Specify the format for the output object file. The only supported *format* is **binary**, which produces output with no ELF header. - **--omagic**, **-N** Set the text and data sections to be readable and writable. - **--opt-remarks-filename** *file* Write optimization remarks in YAML format to *file*. - **--opt-remarks-with-hotness** Include hotness information in the optimization remarks file. - **--pie** Create a position independent executable. - **--print-gc-sections** List removed unused sections. - **--print-map** Print a link map to the standard output. - **--push-state** Save the current state of **--as-needed**, **--static**, and **--while-archive.** - **--pop-state** Undo the effect of **--push-state.** - **--relocatable**, **-r** Create relocatable object file. - **--reproduce**=*value* Dump linker invocation and input files for debugging. - **--retain-symbols-file**=*file* Retain only the symbols listed in the file. - **--rpath**=*value*, **-R** *value* Add a DT\_RUNPATH to the output. - **--rsp-quoting**=*value* Quoting style for response files. The supported values are **windows** and **posix**. - **--script**=*file*, **-T** *file* Read linker script from *file*. - **--section-start**=*section*=*address* Set address of section. - **--shared**, **--Bsharable** Build a shared object. - **--soname**=*value*, **-h** *value* Set DT\_SONAME to *value*. - **--sort-section**=*value* Specifies sections sorting rule when linkerscript is used. - **--start-lib** Start a grouping of objects that should be treated as if they were together in an archive. - **--strip-all**, **-s** Strip all symbols. - **--strip-debug**, **-S** Strip debugging information. - **--symbol-ordering-file**=*file* Lay out sections in the order specified by *file*. - **--sysroot**=*value* Set the system root. - **--target1-abs** Interpret R\_ARM\_TARGET1 as R\_ARM\_ABS32. - **--target1-rel** Interpret R\_ARM\_TARGET1 as R\_ARM\_REL32. - **--target2**=*type* Interpret R\_ARM\_TARGET2 as *type*, where *type* is one of **rel**, **abs**, or **got-rel**. - **--Tbss**=*value* Same as **--section-start** with .bss as the sectionname. - **--Tdata**=*value* Same as **--section-start** with .data as the sectionname. - **--Ttext**=*value* Same as **--section-start** with .text as the sectionname. - **--thinlto-cache-dir**=*value* Path to ThinLTO cached object file directory. - **--thinlto-cache-policy**=*value* Pruning policy for the ThinLTO cache. - **--thinlto-jobs**=*value* Number of ThinLTO jobs. - **--threads** Run the linker multi-threaded. This option is enabled by default. - **--trace** Print the names of the input files. - **--trace-symbol**=*symbol*, **-y** *symbol* Trace references to *symbol*. - **--undefined**=*symbol*, **-u** *symbol* Force *symbol* to be an undefined symbol during linking. - **--unresolved-symbols**=*value* Determine how to handle unresolved symbols. - **-v** Display the version number and proceed with linking if object files are specified. - **-V**, **--version** Display the version number and exit. - **--verbose** Verbose mode. - **--version-script**=*file* Read version script from *file*. - **--warn-backrefs** Warn about reverse or cyclic dependencies to or between static archives. This can be used to ensure linker invocation remains compatible with traditional Unix-like linkers. - **--warn-common** Warn about duplicate common symbols. - **--warn-unresolved-symbols** Report unresolved symbols as warnings. - **--whole-archive** Force load of all members in a static library. - **--wrap**=*symbol* Use wrapper functions for symbol. - **-z** *option* Linker option extensions. - **execstack** Make the main stack executable. Stack permissions are recorded in the PT\_GNU\_STACK segment. - **initfirst** Sets the DF\_1\_INITFIRST flag to indicate the module should be initialized first. - **muldefs** Do not error if a symbol is defined multiple times. The first definition will be used. This is a synonym for **--allow-multiple-definition.** - **nocombreloc** Disable combining and sorting multiple relocation sections. - **nocopyreloc** Disable the creation of copy relocations. - **nodelete** Set the DF\_1\_NODELETE flag to indicate that the object cannot be unloaded from a process. - **nodlopen** Set the DF\_1\_NOOPEN flag to indcate that the object may not be opened by [dlopen(3)](/dlopen/3.md). - **norelro** Do not indicate that portions of the object shold be mapped read-only after initial relocation processing. The object will omit the PT\_GNU\_RELRO segment. - **notext** Allow relocations against read-only segments. Sets the DT\_TEXTREL flag in the DYNAMIC section. - **now** Set the DF\_BIND\_NOW flag to indicate that the run-time loader should perform all relocation processing as part of object initialization. By default relocations may be performed on demand. - **origin** Set the DF\_ORIGIN flag to indicate that the object requires $ORIGIN processing. - **retpolineplt** Emit retpoline format PLT entries as a mitigation for CVE-2017-5715. - **rodynamic** Make the .dynamic section read-only. The DT\_DEBUG tag will not be emitted. - **stack-size**=*size* Set the main thread's stack size to *size*. The stack size is recorded as the size of the *size*. PT\_GNU\_STACK program segment. - **text** Do not allow relocations against read-only segments. This is the default. - **wxneeded** Create a PT\_OPENBSD\_WXNEEDED segment. ## IMPLEMENTATION NOTES **ld.lld**'s handing of archive files (those with a *.a* file extension) is different from traditional linkers used on Unix-like systems. Traditional linkers maintain a set of undefined symbols during linking. The linker processes each file in the order in which it appears on the command line, until the set of undefined symbols becomes empty. An object file is linked into the output object when it is encountered, with its undefined symbols added to the set. Upon encountering an archive file a traditional linker searches the objects contained therein, and processes those that satisfy symbols in the unresolved set. Handling mutually dependent archives may be awkward when using a traditional linker. Archive files may have to be specified multiple times, or the special command line options **--start-group** and **--end-group** may be used to have the linker loop over the files in the group until no new symbols are added to the set. **ld.lld** records all symbols found in objects and archives as it iterates over command line arguments. When **ld.lld** encounters an undefined symbol that can be resolved by an object file contained in a previously processed archive file, it immediately extracts and links it into the output object. With certain archive inputs **ld.lld** may produce different results compared to traditional linkers. In practice, large bodies of third party software have been linked with **ld.lld** without material issues. The **--warn-backrefs** option may be used to identify a linker invocation that may be incompatible with traditional Unix-like linker behavior.