Provided by: mold_2.37.1+dfsg-1_amd64 
NAME
mold - a modern linker
SYNOPSIS
mold [option...] file...
DESCRIPTION
mold is a faster drop-in replacement for the default GNU ld(1).
How to use
See https://github.com/rui314/mold#how-to-use.
Compatibility
mold is designed to be a drop-in replacement for the GNU linkers for linking user-land programs. If your
user-land program cannot be built due to missing command-line options, please file a bug at
https://github.com/rui314/mold/issues.
mold supports a very limited set of linker script features, which is just sufficient to read
/usr/lib/x86_64-linux-gnu/libc.so on Linux systems (on Linux, that file is contrary to its name not a
shared library but an ASCII linker script that loads a real libc.so file.)
Beyond that, we have no plan to support any additional linker script features. The linker script is an
ad-hoc, over-designed, complex language which we believe needs to be replaced by a simpler mechanism. We
have a plan to add a replacement for the linker script to mold instead.
Archive symbol resolution
Traditionally, Unix linkers are sensitive to the order in which input files appear on the command line.
They process input files from the first (leftmost) file to the last (rightmost) file one-by-one. While
reading input files, they maintain sets of defined and undefined symbols. When visiting an archive file
(.a files), they pull out object files to resolve as many undefined symbols as possible and move on to
the next input file. Object files that weren't pulled out will never have a chance for a second look.
Due to this behavior, you usually have to add archive files at the end of a command line, so that when a
linker reaches archive files, it knows what symbols remain as undefined.
If you put archive files at the beginning of a command line, a linker doesn't have any undefined symbols,
and thus no object files will be pulled out from archives. You can change the processing order by using
the --start-group and --end-group options, though they make a linker slower.
mold, as well as the LLVM lld(1) linker, takes a different approach. They remember which symbols can be
resolved from archive files instead of forgetting them after processing each archive. Therefore, mold and
lld(1) can "go back" in a command line to pull out object files from archives if they are needed to
resolve remaining undefined symbols. They are not sensitive to the input file order.
--start-group and --end-group are still accepted by mold and lld(1) for compatibility with traditional
linkers, but they are silently ignored.
Dynamic symbol resolution
Some Unix linker features are difficult to understand without comprehending the semantics of dynamic
symbol resolution. Therefore, even though it's not specific to mold, we'll explain it here.
We use "ELF module" or just "module" as a collective term to refer to an executable or a shared library
file in the ELF format.
An ELF module may have lists of imported symbols and exported symbols, as well as a list of shared
library names from which imported symbols should be imported. The point is that imported symbols are not
bound to any specific shared library until runtime.
Here is how the Unix dynamic linker resolves dynamic symbols. Upon the start of an ELF program, the
dynamic linker constructs a list of ELF modules which, as a whole, consist of a complete program. The
executable file is always at the beginning of the list followed by its dependent shared libraries. An
imported symbol is searched from the beginning of the list to the end. If two or more modules define the
same symbol, the one that appears first in the list takes precedence over the others.
This Unix semantics are contrary to systems such as Windows that have a two-level namespace for dynamic
symbols. On Windows, for example, dynamic symbols are represented as a tuple of (symbol-name,
shared-library-name), so that each dynamic symbol is guaranteed to be resolved from some specific
library.
Typically, an ELF module that exports a symbol also imports the same symbol. Such a symbol is usually
resolved to itself, but that's not the case if a module that appears before it in the symbol search list
provides another definition of the same symbol.
Let's take malloc as an example. Assume that you define your version of malloc in your main executable
file. Then, all malloc calls from any module are resolved to your function instead of the one in libc,
because the executable is always at the beginning of the dynamic symbol search list. Note that even
malloc calls within libc are resolved to your definition since libc exports and imports malloc.
Therefore, by defining malloc yourself, you can overwrite a library function, and the malloc in libc
becomes dead code.
These Unix semantics are tricky and sometimes considered harmful. For example, assume that you
accidentally define atoi as a global function in your executable that behaves completely differently from
the one in the C standard. Then, all atoi function calls from any modules (even function calls within
libc) are redirected to your function instead of the one in libc, which will very likely cause a problem.
That is a somewhat surprising consequence for an accidental name conflict. On the other hand, this
semantic is sometimes useful because it allows users to override library functions without rebuilding
modules containing them.
Whether good or bad, you should keep these semantics in mind to understand Unix linkers' behaviors.
Build reproducibility
mold's output is deterministic. That is, if you pass the same object files and the same command-line
options to the same version of mold, it is guaranteed that mold produces the bit-for-bit identical
output. The linker's internal randomness, such as the timing of thread scheduling or iteration orders of
hash tables, doesn't affect the output.
mold does not have any host-specific default settings. This is contrary to the GNU linkers, for which
some configurable values, such as system-dependent library search paths, are hard-coded. mold depends
only on its command-line arguments.
OPTION NOTATIONS
Multi-letter long options may precede either a single dash or double dashes, except for those starting
with the letter "o". For historical reasons, long options beginning with "o" must precede double dashes.
For example, you can spell --as-needed as -as-needed, but --omagic must not be spelled as -omagic.
-omagic will be interpreted not as --omagic but as -o magic.
MOLD-SPECIFIC OPTIONS
--chroot=dir
Set dir as the root directory.
--color-diagnostics=[ auto | always | never ]
Show diagnostic messages in color using ANSI escape sequences. auto means that mold prints out
messages in color only if the standard output is connected to a TTY. Default is auto.
--color-diagnostics
Synonym for --color-diagnostics=auto.
--no-color-diagnostics
Synonym for --color-diagnostics=never.
--detach, --no-detach
Permit or do not permit mold to create a debug info file in the background.
--fork, --no-fork
Spawn a child process and let it do the actual linking. When linking a large program, the OS
kernel can take a few hundred milliseconds to terminate a mold process. --fork hides that latency.
By default, it does fork.
--perf Print performance statistics.
--print-dependencies
Print out dependency information for input files.
Each line of the output for this option shows which file depends on which file to use a specific
symbol. This option is useful for debugging why some object file in a static archive got linked or
why some shared library is kept in an output file's dependency list even with --as-needed.
--relocatable-merge-sections
By default, mold doesn't merge input sections by name when merging input object files into a
single output object file for -r. For example, .text.foo and .text.bar aren't merged for -r even
though they are merged into .text based on the default section merging rules.
This option changes the behavior so that mold merges input sections by name by the default section
merging rules.
--repro
Archive input files, as well as a text file containing command line options, in a tar file so that
you can run mold with the exact same inputs again. This is useful for reporting a bug with a
reproducer. The output filename is path/to/output.tar, where path/to/output is an output filename
specified by -o.
--reverse-sections
Reverse the order of input sections before assigning them the offsets in the output file.
This option is useful for finding bugs that depend on the initialization order of global objects.
In C++, constructors of global objects in a single source file are guaranteed to be executed in
the source order, but there's no such guarantee across compilation units. Usually, constructors
are executed in the order given to the linker, but depending on it is a mistake.
By reversing the order of input sections using --reverse-sections, you can easily test that your
program works in the reversed initialization order.
--run command arg...
Run command with mold as /usr/bin/ld. Specifically, mold runs a given command with the LD_PRELOAD
environment set to intercept exec(3) family functions and replaces argv[0] with itself if it is
ld, ld.gold, or ld.lld.
--separate-debug-file, --separate-debug-file=file
Bundle debug info sections into a separate file instead of embedding them in an output executable
or a shared library. mold creates a debug info file in the background by default, so that you can
start running your executable as soon as possible.
By default, the debug info file is created in the same directory as is the output file, with the
.dbg file extension. That filename is embedded into the output file so that gdb can automatically
find the debug info file for the output file. For more info about gdb features related to separate
debug files, see https://sourceware.org/gdb/current/onlinedocs/gdb.html/Separate-Debug-Files.html.
mold holds a file lock with flock(2) while creating a debug info file in the background.
If you don't want to create a debug info file in the background, pass the --no-detach option.
--shuffle-sections, --shuffle-sections=number
Randomize the output by shuffling the order of input sections before assigning them the offsets in
the output file. If a number is given, it's used as a seed for the random number generator, so
that the linker produces the same output for the same seed. If no seed is given, a random number
is used as a seed.
This option is useful for benchmarking. Modern CPUs are sensitive to a program's memory layout. A
seemingly benign change in program layout, such as a small size increase of a function in the
middle of a program, can affect the program's performance. Therefore, even if you write new code
and get a good benchmark result, it is hard to say whether the new code improves the program's
performance; it is possible that the new memory layout happens to perform better.
By running a benchmark multiple times with randomized memory layouts using --shuffle-sections, you
can isolate your program's real performance number from the randomness caused by memory layout
changes.
--spare-program-headers=number
Append the given number of PT_NULL entries to the end of the program header, so that post-link
processing tools can easily add new segments by overwriting the null entries.
Note that ELF requires all PT_LOAD segments to be sorted by p_vaddr. Therefore, if you add a new
LOAD segment, you may need to sort the entire program header.
--stats
Print input statistics.
--thread-count=count
Use count number of threads.
--threads, --no-threads
Use multiple threads. By default, mold uses as many threads as the number of cores or 32,
whichever is smaller. The reason it is capped at 32 is because mold doesn't scale well beyond that
point. To use only one thread, pass --no-threads or --thread-count=1.
--quick-exit, --no-quick-exit
Use or do not use quick_exit to exit.
-z rewrite-endbr, -z norewrite-endbr
As a security measure, some CPU instruction sets have recently gained a feature to protect control
flow integrity by disallowing indirect branches by default. If the feature is enabled, the
instruction that is executed immediately after an indirect branch must be an branch target marker
instruction, or a CPU-level fault will raise. The marker instruction is also known as "landing
pad" instruction, to which indirect branches can land. This feature makes ROP attacks harder to
conduct.
To use the feature, a function whose pointer is taken needs to begin with a landing pad because a
function call via a function pointer is compiled to an indirect branch. On the other hand, if a
function is called only directly (i.e. referred to only by direct branch instructions), it doesn't
have to begin with it.
By default, the compiler always emits a landing pad at the beginning of each global function
because it doesn't know whether or not the function's pointer is taken in another translation
unit. As a result, the resulting binary has more attack surface than necessary.
If --rewrite-endbr is given, mold conducts a whole program analysis to identify functions whose
addresses are actually taken and rewrites landing pads with no-ops for non-address-taken
functions, reducing the attack surface.
This feature is currently available only on x86-64.
GNU-COMPATIBLE OPTIONS
--help Report usage information to stdout and exit.
-v, --version
Report version information to stdout.
-V Report version and target information to stdout.
-E, --export-dynamic, --no-export-dynamic
When creating an executable, using the -E option causes all global symbols to be put into the
dynamic symbol table, so that the symbols are visible from other ELF modules at runtime.
By default, or if --no-export-dynamic is given, only symbols that are referenced by DSOs at
link-time are exported from an executable.
-F libname, --filter=libname
Set the DT_FILTER dynamic section field to libname.
-I file, --dynamic-linker=file, --no-dynamic-linker
Set the dynamic linker path to file. If no -I option is given, or if --no-dynamic-linker is given,
no dynamic linker path is set to an output file. This is contrary to the GNU linkers which set a
default dynamic linker path in that case. This difference doesn't usually make any difference
because the compiler driver always passes -I to the linker.
-L dir, --library-path=dir
Add dir to the list of library search paths from which mold searches libraries for the -l option.
Unlike the GNU linkers, mold does not have default search paths. This difference doesn't usually
make any difference because the compiler driver always passes all necessary search paths to the
linker.
-M, --print-map
Write a map file to stdout.
-N, --omagic, --no-omagic
Force mold to emit an output file with an old-fashioned memory layout. First, it makes the first
data segment not aligned to a page boundary. Second, text segments are marked as writable if the
option is given.
-S, --strip-debug
Omit .debug_* sections from the output file.
-T file, --script=file
Read linker script from file.
-X, --discard-locals
Discard temporary local symbols to reduce the sizes of the symbol table and the string table.
Temporary local symbols are local symbols starting with .L. Compilers usually generate such
symbols for unnamed program elements such as string literals or floating-point literals.
-e symbol, --entry=symbol:
-f shlib, --auxiliary=shlib
Set the DT_AUXILIARY dynamic section field to shlib.
-h libname, --soname=libname
Set the DT_SONAME dynamic section field to libname. This option is used when creating a shared
object file. Typically, when you create libfoo.so, you want to pass --soname=foo to a linker.
-l libname
Search for liblibname.so or liblibname.a from library search paths.
-m target
Choose a target.
-o file, --output=file
Use file as the output file name instead of the default name a.out.
-r, --relocatable
Instead of generating an executable or a shared object file, combine input object files to
generate another object file that can be used as an input to a linker.
-s, --strip-all
Omit .symtab section from the output file.
-u symbol, --undefined=symbol
If symbol remains as an undefined symbol after reading all object files, and if there is a static
archive that contains an object file defining symbol, pull out the object file and link it so that
the output file contains a definition of symbol.
-y symbol, --trace-symbol=symbol
Trace references to symbol.
--Bdynamic
Link against shared libraries.
--Bstatic
Do not link against shared libraries.
--Bsymbolic
When creating a shared library, make global symbols export-only (i.e. do not import the same
symbol). As a result, references within a shared library are always resolved locally, negating
symbol override at runtime. See "Dynamic symbol resolution" for more information about symbol
imports and exports.
--Bsymbolic-functions
This option has the same effect as --Bsymbolic but works only for function symbols. Data symbols
remain being both imported and exported.
--Bsymbolic-non-weak
This option has the same effect as --Bsymbolic but works only for non-weak symbols. Weak symbols
remain being both imported and exported.
--Bsymbolic-non-weak-functions
This option has the same effect as --Bsymbolic but works only for non-weak function symbols. Data
symbols and weak function symbols remain being both imported and exported.
--Bno-symbolic
Cancel --Bsymbolic, --Bsymbolic-functions, --Bsymbolic-non-weak and
--Bsymbolic-non-weak-functions.
--Map=file
Write map file to file.
--Tbss=address
Alias for --section-start=.bss=address.
--Tdata=address
Alias for --section-start=.data=address.
--Ttext=address
Alias for --section-start=.text=address.
--allow-multiple-definition
Normally, the linker reports an error if there are more than one definition of a symbol. This
option changes the default behavior so that it doesn't report an error for duplicate definitions
and instead use the first definition.
--allow-shlib-undefined, --no-allow-shlib-undefined
Even if mold succeeds in linking a main executable without undefined symbol errors, you may still
encounter symbol lookup errors at runtime because the dynamic linker cannot find some symbols in
shared libraries in any ELF module. This occurs because mold ignores undefined symbols in shared
libraries by default.
If you pass --no-allow-shlib-undefined, mold verifies that undefined symbols in shared libraries
given to the linker can be resolved at link-time. In other words, this converts the runtime error
to a link-time error.
Note that you need to pass all shared libraries, including indirectly dependent ones, to the
linker as arguments for -l. If a shared library depends on a library that's not passed to the
linker, the verification will be skipped for that file.
--as-needed, --no-as-needed
By default, shared libraries given to the linker are unconditionally added to the list of required
libraries in an output file. However, shared libraries after --as-needed are added to the list
only when at least one symbol is actually used by the output file. In other words, shared
libraries after --as-needed are not added to the list of needed libraries if they are not needed
by a program.
The --no-as-needed option restores the default behavior for subsequent files.
--build-id=[ md5 | sha1 | sha256 | fast | uuid | 0xhexstring | none ]
Create a .note.gnu.build-id section containing a byte string to uniquely identify an output file.
sha256 compute a 256-bit cryptographic hash of an output file and set it to build-id. md5 and sha1
compute the same hash but truncate it to 128 and 160 bits, respectively, before setting it to
build-id. uuid sets a random 128-bit UUID. 0xhexstring sets hexstring. fast is a synonym for
sha256.
--build-id
Synonym for --build-id=sha256.
--no-build-id
Synonym for --build-id=none.
--compress-debug-sections=[ zlib | zlib-gabi | zstd | none ]
Compress DWARF debug info (.debug_* sections) using the zlib or zstd compression algorithm.
zlib-gabi is an alias for zlib.
--defsym=symbol=value
Define symbol as an alias for value.
value is either an integer (in decimal or hexadecimal with 0x prefix) or a symbol name. If an
integer is given as a value, symbol is defined as an absolute symbol with the given value.
--default-symver
Use soname as a symbol version and append that version to all symbols.
--demangle, --no-demangle
Demangle C++ and Rust symbols in log messages.
--dependency-file=file
Write a dependency file to file. The contents of the written file is readable by make(1), which
defines only one rule with the linker's output file as a target and all input files as its
prerequisites. Users are expected to include the generated dependency file into a Makefile to
automate the dependency management. This option is analogous to the compiler's -MM -MF options.
--dynamic-list=file
Read a list of dynamic symbols from file. Same as --export-dynamic-symbol-list, except that it
implies --Bsymbolic. If file does not exist in the current directory, it is searched from library
search paths for the sake of compatibility with GNU ld.
--eh-frame-hdr, --no-eh-frame-hdr
Create .eh_frame_hdr section.
--emit-relocs
The linker usually "consumes" relocation sections. That is, the linker applies relocations to
other sections, and relocation sections themselves are discarded.
The --emit-relocs instructs the linker to leave relocation sections in the output file. Some
post-link binary analysis or optimization tools such as LLVM Bolt need them.
--enable-new-dtags, --disable-new-dtags
By default, mold emits DT_RUNPATH for --rpath. If you pass --disable-new-dtags, mold emits
DT_RPATH for --rpath instead.
--execute-only:
--exclude-libs=libraries ...
Mark all symbols in the given libraries hidden.
--export-dynamic-symbol=symbol
Put symbols matching symbol in the dynamic symbol table. symbol may be a glob pattern in the same
syntax as for the --export-dynamic-symbol-list or --version-script options.
--export-dynamic-symbol-list=file
Read a list of dynamic symbols from file.
--fatal-warnings, --no-fatal-warnings
Treat warnings as errors.
--fini=symbol
Call symbol at unload-time.
--gc-sections, --no-gc-sections
Remove unreferenced sections.
--gdb-index
Create a .gdb_index section to speed up GNU debugger. To use this, you need to compile source
files with the -ggnu-pubnames compiler flag.
--hash-style=[ sysv | gnu | both | none ]
Set hash style.
--icf=[ safe | all | none ], --no-icf
It is not uncommon for a program to contain many identical functions that differ only in name. For
example, a C++ template std::vector is very likely to be instantiated to the identical code for
std::vector<int> and std::vector<unsigned> because the container cares only about the size of the
parameter type. Identical Code Folding (ICF) is a size optimization to identify and merge such
identical functions.
If --icf=all is given, mold tries to merge all identical functions. This reduces the size of the
output most, but it is not a "safe" optimization. It is guaranteed in C and C++ that two pointers
pointing two different functions will never be equal, but --icf=all breaks that assumption as two
identical functions have the same address after merging. So a care must be taken when you use this
flag that your program does not depend on the function pointer uniqueness.
--icf=safe is a flag to merge functions only when it is safe to do so. That is, if a program does
not take an address of a function, it is safe to merge that function with other function, as you
cannot compare a function pointer with something else without taking an address of a function.
--icf=safe needs to be used with a compiler that supports .llvm_addrsig section which contains the
information as to what symbols are address-taken. LLVM/Clang supports that section by default.
Since GCC does not support it yet, you cannot use --icf=safe with GCC (it doesn't do any harm but
can't optimize at all.)
--icf=none and --no-icf disables ICF.
--ignore-data-address-equality
Make ICF to merge not only functions but also data. This option should be used in combination with
--icf=all.
--image-base=addr
Set the base address to addr.
--init=symbol
Call symbol at load-time.
--no-undefined
Report undefined symbols (even with --shared).
--noinhibit-exec
Create an output file even if errors occur.
--package-metadata=percent-encoded-string
Embed a specified string into the .note.package section. This option is designed for build scripts
that generate binary packages, such as .rpm or .deb, to include package metadata in each
executable. It simplifies the process of identifying the corresponding package for a given
executable or core file.
An argument to this option is treated as percent-encoded and decoded before being inserted into
the section, allowing you to avoid the use of the comma (,) character in the argument. This is
useful because the compiler replaces all occurrences of commas in -Wl, with spaces before
forwarding them to the linker. Note that mold always interprets the argument as percent-encoded,
so you also need to escape all occurrences of % as %25.
--pack-dyn-relocs=[ relr | none ]
If relr is specified, all R_*_RELATIVE relocations are put into .relr.dyn section instead of
.rel.dyn or .rela.dyn section. Since .relr.dyn section uses a space-efficient encoding scheme,
specifying this flag can reduce the size of the output. This is typically most effective for
position-independent executable.
Note that a runtime loader has to support .relr.dyn to run executables or shared libraries linked
with --pack-dyn-relocs=relr. As of 2022, only ChromeOS, Android and Fuchsia support it.
--pie, --pic-executable, --no-pie, --no-pic-executable
Create a position-independent executable.
--print-gc-sections, --no-print-gc-sections
Print removed unreferenced sections.
--print-icf-sections, --no-print-icf-sections
Print folded identical sections.
--push-state, --pop-state
--push-state saves the current values of --as-needed, --whole-archive, --static, and --start-lib.
The saved values can be restored by pop-state.
--push-state and --pop-state pairs can nest.
These options are useful when you want to construct linker command line options programmatically.
For example, if you want to link libfoo.so by as-needed basis but don't want to change the global
state of --as-needed, you can append --push-state --as-needed -lfoo --pop-state to the linker
command line options.
--relax, --no-relax
Rewrite machine instructions with more efficient ones for some relocations. The feature is enabled
by default.
--require-defined=symbol
Like --undefined, except the new symbol must be defined by the end of the link.
--retain-symbols-file=file
Keep only symbols listed in file. file is a text file containing a symbol name on each line. mold
discards all local symbols as well as global symbol that are not in file. Note that this option
removes symbols only from .symtab section and does not affect .dynsym section, which is used for
dynamic linking.
--rpath=dir
Add dir to runtime search paths.
--section-start=section=address
Set address to section. address is a hexadecimal number that may start with an optional 0x.
--shared, --Bshareable
Create a share library.
--spare-dynamic-tags=number
Append the given number of DT_NULL entries to the end of the .dynamic section, so that post-link
processing tools can easily add new dynamic tags by overwriting the null entries.
--start-lib, --end-lib
Handle object files between --start-lib and --end-lib as if they were in an archive file. That
means object files between them are linked only when they are needed to resolve undefined symbols.
The options are useful if you want to link object files only when they are needed but want to
avoid the overhead of running ar(3).
--static
Do not link against shared libraries.
--sysroot=dir
Set target system root directory to dir.
--trace
Print name of each input file.
--undefined-glob=pattern
Synonym for --undefined, except that --undefined-glob takes a glob pattern instead of just a
single symbol name.
--undefined-version, --no-undefined-version
By default, mold warns on a symbol specified by a version script or by --export-dynamic-symbol if
it is not defined. You can silence the warning by --undefined-version.
--unique=pattern
Don't merge input sections that match the given glob pattern pattern.
--unresolved-symbols=[ report-all | ignore-all | ignore-in-object-files | ignore-in-shared-libs ]
How to handle undefined symbols.
--version-script=file
Read version script from file. If file does not exist in the current directory, it is searched
from library search paths for the sake of compatibility with GNU ld.
--warn-common, --no-warn-common
Warn about common symbols.
--warn-once
Only warn once for each undefined symbol instead of warn for each relocation referring an
undefined symbol.
--warn-unresolved-symbols, --error-unresolved-symbols
Normally, the linker reports an error for unresolved symbols. --warn-unresolved-symbols option
turns it into a warning. --error-unresolved-symbols option restores the default behavior.
--whole-archive, --no-whole-archive
When archive files (.a files) are given to the linker, only object files that are needed to
resolve undefined symbols are extracted from them and linked to an output file. --whole-archive
changes that behavior for subsequent archives so that the linker extracts all object files and
links them to an output. For example, if you are creating a shared object file and you want to
include all archive members to the output, you should pass --whole-archive. --no-whole-archive
restores the default behavior for subsequent archives.
--wrap=symbol
Make symbol be resolved to __wrap_symbol. The original symbol can be resolved as __real_symbol.
This option is typically used for wrapping an existing function.
-z cet-report=[ warning | error | none ]
Intel Control-flow Enforcement Technology (CET) is a new x86 feature available since Tiger Lake
which is released in 2020. It defines new instructions to harden security to protect programs from
control hijacking attacks. You can tell the compiler to use the feature by specifying the
-fcf-protection flag.
-z cet-report flag is used to make sure that all object files were compiled with a correct
-fcf-protection flag. If warning or error are given, mold prints out a warning or an error message
if an object file was not compiled with the compiler flag.
mold looks for GNU_PROPERTY_X86_FEATURE_1_IBT bit and GNU_PROPERTY_X86_FEATURE_1_SHSTK bit in
.note.gnu.property section to determine whether or not an object file was compiled with
-fcf-protection.
-z now, -z lazy
By default, functions referring to other ELF modules are resolved by the dynamic linker when they
are called for the first time. -z now marks an executable or a shared library file so that all
dynamic symbols are resolved when a file is loaded to memory. -z lazy restores the default
behavior.
-z origin
Mark object requiring immediate $ORIGIN processing at runtime.
-z ibt Turn on GNU_PROPERTY_X86_FEATURE_1_IBT bit in .note.gnu.property section to indicate that the
output uses IBT-enabled PLT. This option implies -z ibtplt.
-z ibtplt
Generate Intel Branch Tracking (IBT)-enabled PLT which is the default on x86-64. This is the
default.
-z execstack, -z noexecstack
By default, the pages for the stack area (i.e. the pages where local variables reside) are not
executable for security reasons. -z execstack makes it executable. -z noexecstack restores the
default behavior.
-z keep-text-section-prefix, -z nokeep-text-section-prefix
Keep .text.hot, .text.unknown, .text.unlikely, .text.startup, and .text.exit as separate sections
in the final binary instead of merging them as .text.
-z rodynamic
Make the .dynamic section read-only.
-z relro, -z norelro
Some sections such as .dynamic have to be writable only during a module is being loaded to memory.
Once the dynamic linker finishes its job, such sections won't be mutated by anyone. As a security
mitigation, it is preferred to make such segments read-only during program execution.
-z relro puts such sections into a special segment called relro. The dynamic linker makes a relro
segment read-only after it finishes its job.
By default, mold generates a relro segment. -z norelro disables the feature.
-z sectionheader, -z nosectionheader
-z nosectionheader tell the linker to omit the section header. By default, the linker does not
omit the section header.
-z separate-loadable-segments, -z separate-code, -z noseparate-code
If one memory page contains multiple segments, the page protection bits are set in such a way that
the needed attributes (writable or executable) are satisfied for all segments. This usually
happens at a boundary of two segments with two different attributes.
separate-loadable-segments adds paddings between segments with different attributes so that they
do not share the same page. This is the default.
separate-code adds paddings only between executable and non-executable segments.
noseparate-code does not add any paddings between segments.
-z defs, -z nodefs
Report undefined symbols (even with --shared).
-z shstk
Enforce shadow stack by turning GNU_PROPERTY_X86_FEATURE_1_SHSTK bit in .note.gnu.property output
section. Shadow stack is part of Intel Control-flow Enforcement Technology (CET), which is
available since Tiger Lake (2020).
-z start_stop_visibility=[ hidden | protected ]
If a section name is valid as a C identifier (i.e., it matches /^[_a-zA-Z][_a-zA-Z0-9]*$/), mold
creates __start_SECNAME and __stop_SECNAME symbols to mark the beginning and end of the section,
where SECNAME is the section name.
You can make these marker symbols visible from other ELF modules by passing -z
start_stop_visibility=protected. Default is hidden.
-z text, -z notext, -z textoff
mold by default reports an error if dynamic relocations are created in read-only sections. If -z
notext or -z textoff are given, mold creates such dynamic relocations without reporting an error.
-z text restores the default behavior.
-z max-page-size=number
Some CPU ISAs support multiple memory page sizes. This option specifies the maximum page size that
an output binary can run on. In general, binaries built for a larger page size can run on a system
with a smaller page size, but not vice versa. The default value is 4 KiB for i386, x86-64, and
RISC-V, and 64 KiB for ARM64.
-z nodefaultlib
Make the dynamic loader ignore default search paths.
-z nodelete
Mark DSO non-deletable at runtime.
-z nodlopen
Mark DSO not available to dlopen(3). This option makes it possible for the linker to optimize
thread-local variable accesses by rewriting instructions for some targets.
-z nodump
Mark DSO not available to dldump(3).
-z nocopyreloc
Do not create copy relocations.
-z initfirst
Mark DSO to be initialized first at runtime.
-z interpose
Mark object to interpose all DSOs but executable.
-(, -), -EL, -Onumber, --dc, --dp, --end-group, --no-add-needed, --no-copy-dt-needed-entries, --nostdlib,
--rpath-link=Ar dir, --sort-common, --sort-section, --start-group, --warn-constructors, --warn-once,
--fix-cortex-a53-835769, --fix-cortex-a53-843419, -z combreloc, -z common-page-size, -z nocombreloc
Ignored
ENVIRONMENT VARIABLES
MOLD_JOBS
If this variable is set to 1, only one mold process will run at a time. If a new mold process is
initiated while another is already active, the new process will wait until the active one
completes before starting.
The primary reason for this environment variable is to minimize peak memory usage. Since mold is
designed to operate with high parallelism, running multiple mold instances simultaneously may not
be beneficial. If you execute N instances of mold concurrently, it could require N times the time
and N times the memory. On the other hand, running them one after the other might still take N
times longer, but the peak memory usage would be the same as running just a single instance.
If your build system invokes multiple linker processes simultaneously and some of them often get
killed due to out-of-memory errors, you might consider setting this environment variable to 1 to
see if it addresses the OOM issue.
Currently, any value other than 1 is silently ignored.
MOLD_DEBUG
If this variable is set to a non-empty string, mold embeds its command-line options in the output
file's .comment section.
MOLD_REPRO
Setting this variable to a non-empty string has the same effect as passing the --repro option.
SEE ALSO
gold(1), ld(1), elf(5), ld.so(8)
AUTHOR
Rui Ueyama ruiu@cs.stanford.edu
BUGS
Report bugs to https://github.com/rui314/mold/issues.
February 2025 MOLD(1)