Provided by: mold_2.34.1+dfsg-1ubuntu1_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-by-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.
--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.
August 2024 MOLD(1)