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Write man page in Markdown instead of mandoc

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mandoc is hard to read and hard to write. With `ronn` command, we can
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README.md
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@ -222,9 +222,9 @@ If `mold` is in `.comment`, the file is created by mold.
<details><summary>Online manual</summary>
Since mold is a drop-in replacement, you should be able to use it
without reading its manual. But just in case you need it, it's available
online at <a href=https://rui314.github.io/mold.html>here</a>.
You can also read the same manual by `man mold`.
without reading its manual. But just in case you need it,
[mold's man page](docs/mold.md) is also available. You can read the
same manual by `man mold`.
</details>

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docs/mold.1
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mold(1) -- 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 despite 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 linker script features. The linker
script is an ad-hoc, over-designed, complex language which we believe needs to
be disrupted 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 command line. They process input files from the first (left-most)
file to the last (right-most) 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 go 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 semantics, 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 are remain undefined.
If you put archive files at the beginning of a command line, a linker doesn't
have any undefined symbol, and thus no object files will be pulled out from
archives.
You can change the processing order by `--start-group` and `--end-group`
options, though they make a linker slower.
`mold` as well as LLVM lld(1) linker take a different approach. They
memorize what symbols can be resolved from archive files instead of forgetting
it 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 unable to be understood without understanding
the semantics of dynamic symbol resolution. Therefore, even though that's not
specific to `mold`, we'll explain it here.
We use "ELF module" or just "module" as a collective term to refer 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 construct 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 depending 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 the
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 in the symbol search list provides another
definition of the same symbol.
Let me take malloc(3) as an example. Assume that you define your version of
malloc(3) in your main executable file. Then, all `malloc` calls from any
module are resolved to your function instead of that in libc, because the
executable is always at the beginning of the dynamic symbol search list. Note
that even malloc(3) 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(3) in libc becomes dead
code.
These Unix semantics are tricky and sometimes considered harmful. For example,
assume that you accidentally define atoi(3) 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
obviously causes a problem.
That is a somewhat surprising consequence for an accidental name conflict. On
the other hand, this semantic is sometimes considered useful because it allows
users to overwrite library functions without recompiling modules containing
them.
Whether good or bad, you should keep this semantic in mind to understand the
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 to always produce the same 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 to which some configurable values, such as system-dependent
library search paths, are hard-coded. `mold` depends only on its command-line
arguments.
## MOLD-SPECIFIC OPTIONS
* `--chroot`=_module_:
Set _module_ to root directory.
* `--color-diagnostics`=[ _auto_ | _always_ | _never_ ]:
Show diagnostics 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`.
* `--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 that which file depends on
which file to use which symbol. This option is useful to debug 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`.
* `--omagic`, `--no-omagic`:
Force `mold` to emit an output file with an old-fashioned memory layout.
First, it makes the first data segment to not be aligned to a page
boundary. Second, text segments are marked as writable if the option is
given.
* `--repro`:
Archive input files as a tar file.
* `--reverse-sections`:
Reverses the order of input sections before assigning them the offsets in
the output file.
This option is useful for finding a bug that depends on an 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` `/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`.
* `--shuffle-sections`, `--shuffle-sections`=_number_:
Randomizes the output by shuffling the order of input sections before
assigning them the offsets in the output file. If _number_ is given, it's
used as a seed for the random number generator, so that the linker
produces the same output as 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
program's memory layout. A seeming benign change in program layout (such
as a small size increase of a function in the middle of a program) can
affect program's performance. Therefore, even if you write new code and
get a good benchmark result, it is hard to say whether or not the new code
improves the programs performance. It is possible that the new memory
layout happens to perform better.
By running a benchmark multiple time with shuffling memory layout using
`--shuffle-sections`, you can isolate your program's real performance
number from the randomness caused by memory layout changes.
* `--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 the smallest. The reason why it is
capped to 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.
## 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 sets a default dynamic
linker path in that case. However, this difference doesn't usually make
any difference because the compiler driver always passes `-I` to a 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 the default search paths.
This difference doesn't usually make any difference because the compiler
driver always passes all necessary search paths to a 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 to not be 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_:
Use _symbol_ as the entry point symbol instead of the default entry point
symbol `_start`.
* `-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 `lib`_libname_`.so` or `lib`_libname_`.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.
* `--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` according to the default section merging rules.
This option changes the behavior so that `mold` merges input sections by
name by the default section merging rules.
* `-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 an 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_.
* `--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 is always resolved locally, negating symbol override at runtime.
See "Dynamic symbol resolution" for more information about symbol imports
and exports.
* `--Bsymbolic-functions`:
Have the same effect as `--Bsymbolic` but works only for function symbols.
Data symbols remains being both imported and exported.
* `--Bno-symbolic`:
Cancel `--Bsymbolic` and `--Bsymbolic-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.
* `-as-needed`, `-no-as-needed`:
By default, shared libraries given to a 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 an object 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`=[ `none` | `md5` | `sha1` | `sha256` | `uuid` | _hexstring_ ]:
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. _hexstring_ sets
_hexstring_.
* `--build-id`:
Synonym for `--build-id=sha256`.
* `--no-build-id`:
Synonym for `--build-id=none`.
* `--compress-debug-sections`=[ `none` | `zlib` | `zlib-gabi` | `zstd` ]:
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++ 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 prerequisite. 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`:
A linker usually "consumes" relocation sections. That is, a 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`:
Traditionally, most processors require both executable and readable bits
to 1 to make the page executable, which allows machine code to read itself
as data at runtime. This is actually what an attacker often does after
gaining a limited control of a process to find pieces of machine code they
can use to gain the full control of the process.
As a mitigation, some recent processors allows "execute-only" pages. If a
page is execute-only, you can call a function there as long as you know
its address but can't read it as data.
This option marks text segments execute-only. This option currently works
only on some ARM64 processors.
* `--exclude-libs`=_libraries_ ...:
Mark all symbols in the given _libraries_ hidden.
* `--export-dynamic-symbol`=_sym_:
Put symbols matching _sym_ in the dynamic symbol table. _sym_ may be a
glob, with the same syntax as the globs used in
`--export-dynamic-`_symbol-list_ or `--version-script`.
* `--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`=[ `none` | `safe` | `all` ], `--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 "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 functions have the same address after merging. So a care
must be taken when you use that 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`=[ `none` | `relr` ]:
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`, and only
ChromeOS, Android and Fuchsia support it as of now in 2022.
* `--package-metadata`=_string_:
Embed _string_ to a .note.package section. This option in intended to be
used by a package management command such as rpm(8) to embed metadata
regarding a package to each executable file.
* `--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 `lib`_foo_`.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 path.
* `--section-start=_section_`=_address_:
Set _address_ to _section_. _address_ is a hexadecimal number that may
start with an optional .Sq 0x .
* `--shared`, `-Bshareable`:
Create a share library.
* `--spare-dynamic-tags`=_number_:
Reserve given _number_ of tags in _.dynamic_ section.
* `--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-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 _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 a 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 a linker extracts all object files and link
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_ to 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`=[ `none` | `warning` | `error` ]:
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 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 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 loaded
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.
* `-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.
* `-z relro`, `-z norelro`:
Some sections such as `.dynamic` have to be writable only during an
executable or a shared library file 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 make a relro segment read-only after it finishes its job.
By default, `mold` generates a relro segment. `-z norelro` disables the
feature.
* `-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 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 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`:
Some CPU ISAs support multiple different memory page sizes. This option
specifies the maximum page size that an output binary can run on. If you
specify a large value, the output can run on both large and small page
systems, but it wastes a bit of memory at page boundaries on systems with
small pages.
The default value is 4 KiB for i386, x86-64 and RISC-V, and 64 KiB for ARM64.
* `-z nodefaultlib`:
Make the dynamic loader to 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`, `-O`_number_, `--allow-shlib-undefined`, `--dc`, `--dp`, `--end-group`, `--no-add-needed`, `--no-allow-shlib-undefined`, `--no-copy-dt-needed-entries`, `--no-fatal-warnings`, `--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
## 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>.