LD(1) User Commands LD(1)

NAME


ld - link-editor for object files

SYNOPSIS


ld [-32 | -64] [-a | -r] [-b] [-B direct | -B nodirect]
[-B dynamic | -B static] [-B eliminate] [-B group] [-B local]
[-B reduce] [-B symbolic] [-c name] [-C] [-d y | -d n] [-D token,...]
[-e epsym] [-f name | -F name] [-G] [-h name] [-i] [-I name] [-l x]
[-L path] [-m] [-M mapfile] [-N string] [-o outfile] [-p auditlib]
[-P auditlib] [-Q y | -Q n] [-R path] [-s] [-S supportlib] [-t]
[-u symname] [-V] [-Y P,dirlist] [-z absexec]
[-z allextract | -z defaultextract | -z weakextract] [-z altexec64]
[-z aslr[=state]] [-z assert-deflib] [-z assert-deflib=libname]
[-z combreloc | -z nocombreloc] [-z defs | -z nodefs]
[-z direct | -z nodirect] [-z endfiltee]
[-z fatal-warnings | -z nofatal-warnings] [-z finiarray=function]
[-z globalaudit] [-z groupperm | nogroupperm] [-z guidance[=id,...]]
[-z help] [-z ignore | -z record] [-z initarray=function] [-z initfirst]
[-z interpose] [-z lazyload | -z nolazyload] [-z ld32=arg,...]
[-z ld64=arg,...] [-z loadfltr] [-z muldefs] [-z nocompstrtab]
[-z nodefaultlib] [-z nodelete] [-z nodlopen] [-z nodump] [-z noldynsym]
[-z nopartial] [-z noversion] [-z now] [-z origin]
[-z preinitarray=function] [-z redlocsym] [-z relaxreloc] [-z rescan]
[-z rescan-now] [-z rescan-start ... -z rescan-end] [-z symbolcap]
[-z target=sparc|x86] [-z text | -z textwarn | -z textoff]
[-z type=exec|kmod|reloc|shared] [-z verbose] [-z wrap=symbol]
filename...

DESCRIPTION


The link-editor, ld, combines relocatable object files by resolving symbol
references to symbol definitions, together with performing relocations. ld
operates in two modes, static or dynamic, as governed by the -d option. In
all cases, the output of ld is left in the file a.out by default. See
NOTES.

In dynamic mode, -d y, the default, relocatable object files that are
provided as arguments are combined to produce an executable object file.
This file is linked at execution with any shared object files that are
provided as arguments. If the -G option is specified, relocatable object
files are combined to produce a shared object. Without the -G option, a
dynamic executable is created.

In static mode, -d n, relocatable object files that are provided as
arguments are combined to produce a static executable file. If the -r
option is specified, relocatable object files are combined to produce one
relocatable object file. See Static Executables.

Dynamic linking is the most common model for combining relocatable objects,
and the eventual creation of processes within illumos. This environment
tightly couples the work of the link-editor and the runtime linker,
ld.so.1(1). Both of these utilities, together with their related
technologies and utilities, are extensively documented in the Linker and
Libraries Guide.

If any argument is a library, ld by default searches the library exactly
once at the point the library is encountered on the argument list. The
library can be either a shared object or relocatable archive. See
ar.h(3HEAD).

A shared object consists of an indivisible, whole unit that has been
generated by a previous link-edit of one or more input files. When the
link-editor processes a shared object, the entire contents of the shared
object become a logical part of the resulting output file image. The
shared object is not physically copied during the link-edit as its actual
inclusion is deferred until process execution. This logical inclusion
means that all symbol entries defined in the shared object are made
available to the link-editing process. See Chapter 4, Shared Objects, in
Linker and Libraries Guide.

For an archive library, ld loads only those routines that define an
unresolved external reference. ld searches the symbol table of the archive
library sequentially to resolve external references that can be satisfied
by library members. This search is repeated until no external references
can be resolved by the archive. Thus, the order of members in the library
is functionally unimportant, unless multiple library members exist that
define the same external symbol. Archive libraries that have
interdependencies can require multiple command line definitions, or the use
of one of the -z rescan options. See Archive Processing in Linker and
Libraries Guide.

ld is a cross link-editor, able to link 32-bit objects or 64-bit objects,
for Sparc or x86 targets. ld uses the ELF class and machine type of the
first relocatable object on the command line to govern the mode in which to
operate. The mixing of 32-bit objects and 64-bit objects is not permitted.
Similarly, only objects of a single machine type are allowed. See the -32,
-64 and -z target options, and the LD_NOEXEC_64 environment variable.

Static Executables


The creation of static executables is discouraged. Since a static
executable is built against system archive libraries, the executable
contains system implementation details. This self-containment has a number
of drawbacks.

+o The executable is immune to the benefits of system updates
delivered as shared objects. The executable therefore, must be
rebuilt to take advantage of many system improvements.

+o The ability of the executable to run on future releases can be
compromised.

+o The duplication of system implementation details negatively affects
system performance.

On illumos, system archive libraries (such as libc.a) have never been
provided. Without these libraries, the creation of static executables is
not achievable without specialized system knowledge. However, the
capability of ld to process static linking options, and the processing of
archive libraries, remains.

OPTIONS


The following options are supported.

-32 | -64
Creates a 32-bit, or 64-bit object.

By default, the class of the object being generated is determined
from the first ELF object processed from the command line. If no
objects are specified, the class is determined by the first object
encountered within the first archive processed from the command line.
If there are no objects or archives, the link-editor creates a 32-bit
object.

The -64 option is required to create a 64-bit object solely from a
mapfile.

The -32 or -64 options can also be used in the rare case of linking
entirely from an archive that contains a mixture of 32 and 64-bit
objects. If the first object in the archive is not the class of the
object that is required to be created, then the -32 or -64 option can
be used to direct the link-editor. See The 32-bit link-editor and
64-bit link-editor in Linker and Libraries Guide.

Note that for compatibility with existing Makefiles and scripts,
these options may be given multiple times and may be mixed in the
same invocation: the last instance wins, so that, for example, `ld
-64 -32 -64 ...' gives 64-bit output.

-a In static mode only, produces an executable object file. Undefined
references are not permitted. This option is the default behavior
for static mode. The -a option can not be used with the -r option.
See Static Executables

-b In dynamic mode only, provides no special processing for dynamic
executable relocations that reference symbols in shared objects.
Without the -b option, the link-editor applies techniques within a
dynamic executable so that the text segment can remain read-only.
One technique is the creation of special position-independent
relocations for references to functions that are defined in shared
objects. Another technique arranges for data objects that are
defined in shared objects to be copied into the memory image of an
executable at runtime.

The -b option is intended for specialized dynamic objects and is not
recommended for general use. Its use suppresses all specialized
processing required to ensure an object's shareability, and can even
prevent the relocation of 64-bit executables.

-B direct | -B nodirect
These options govern direct binding. -B direct establishes direct
binding information by recording the relationship between each symbol
reference together with the dependency that provides the definition.
In addition, direct binding information is established between each
symbol reference and an associated definition within the object being
created. The runtime linker uses this information to search directly
for a symbol in the associated object rather than to carry out a
default symbol search.

Direct binding information can only be established to dependencies
specified with the link-edit. Thus, you should use the -z defs
option. Objects that wish to interpose on symbols in a direct
binding environment should identify themselves as interposers with
the -z interpose option. The use of -B direct enables -z lazyload
for all dependencies.

The -B nodirect option prevents any direct binding to the interfaces
offered by the object being created. The object being created can
continue to directly bind to external interfaces by specifying the -z
direct option. See Appendix D, Direct Bindings, in Linker and
Libraries Guide.

-B dynamic | -B static
Options governing library inclusion. -B dynamic is valid in dynamic
mode only. These options can be specified any number of times on the
command line as toggles: if the -B static option is given, no shared
objects are accepted until -B dynamic is seen. See the -l option.

-B eliminate
Causes any global symbols, not assigned to a version definition, to
be eliminated from the symbol table. Version definitions can be
supplied by means of a mapfile to indicate the global symbols that
should remain visible in the generated object. This option achieves
the same symbol elimination as the auto-elimination directive that is
available as part of a mapfile version definition. This option can
be useful when combining versioned and non-versioned relocatable
objects. See also the -B local and -B reduce options. See Defining
Additional Symbols with a mapfile in Linker and Libraries Guide.

-B group
Establishes a shared object and its dependencies as a group. Objects
within the group are bound to other members of the group at runtime.
This mode is similar to adding the object to the process by using
dlopen(3C) with the RTLD_GROUP mode. An object that has an explicit
dependency on a object identified as a group, becomes a member of the
group.

As the group must be self contained, use of the -B group option also
asserts the -z defs option.

-B local
Causes any global symbols, not assigned to a version definition, to
be reduced to local. Version definitions can be supplied by means of
a mapfile to indicate the global symbols that should remain visible
in the generated object. This option achieves the same symbol
reduction as the auto-reduction directive that is available as part
of a mapfile version definition. This option can be useful when
combining versioned and non-versioned relocatable objects. See also
the -B eliminate and -B reduce options. See Defining Additional
Symbols with a mapfile in Linker and Libraries Guide.

-B reduce
When generating a relocatable object, causes the reduction of
symbolic information defined by any version definitions. Version
definitions can be supplied by means of a mapfile to indicate the
global symbols that should remain visible in the generated object.
By default, when a relocatable object is generated, version
definitions are only recorded in the output image. The actual
reduction of symbolic information is carried out when the object is
used in the construction of a dynamic executable or shared object.
The -B reduce option is applied automatically when a dynamic
executable or shared object is created.

-B symbolic
In dynamic mode only. When building a shared object, binds
references to global symbols to their definitions, if available,
within the object. Normally, references to global symbols within
shared objects are not bound until runtime, even if definitions are
available. This model allows definitions of the same symbol in an
executable or other shared object to override the object's own
definition. ld issues warnings for undefined symbols unless -z defs
overrides.

The -B symbolic option is intended for specialized dynamic objects
and is not recommended for general use. To reduce the runtime
relocation processing that is required an object, the creation of a
version definition is recommended. -c name records the configuration
file name for use at runtime. Configuration files can be employed to
alter default search paths, provide a directory cache, together with
providing alternative object dependencies. See crle(1).

-C Demangles C++ symbol names displayed in diagnostic messages.

-d y | -d n
When -d y, the default, is specified, ld uses dynamic linking. When
-d n is specified, ld uses static linking. See Static Executables
and -B dynamic | -B static.

-D token,...
Prints debugging information as specified by each token to the
standard error. The special token help indicates the full list of
tokens available. See Debugging Aids in Linker and Libraries Guide.

-e epsym
--entry epsym
Sets the entry point address for the output file to be the symbol
epsym.

-f name
--auxiliary name
Useful only when building a shared object. Specifies that the symbol
table of the shared object is used as an auxiliary filter on the
symbol table of the shared object specified by name. Multiple
instances of this option are allowed. This option can not be
combined with the -F option. See Generating Auxiliary Filters in
Linker and Libraries Guide.

-F name
--filter name
Useful only when building a shared object. Specifies that the symbol
table of the shared object is used as a filter on the symbol table of
the shared object specified by name. Multiple instances of this
option are allowed. This option cannot be combined with the -f
option. See Generating Standard Filters in Linker and Libraries
Guide.

-G
-shared
In dynamic mode only, produces a shared object. Undefined symbols
are allowed. See Chapter 4, Shared Objects, in Linker and Libraries
Guide.

-h name
-soname name
In dynamic mode only, when building a shared object, records name in
the object's dynamic section. name is recorded in any dynamic
objects that are linked with this object rather than the object's
file system name. Accordingly, name is used by the runtime linker as
the name of the shared object to search for at runtime. See
Recording a Shared Object Name in Linker and Libraries Guide.

-i Ignores LD_LIBRARY_PATH. This option is useful when an
LD_LIBRARY_PATH setting is in effect to influence the runtime library
search, which would interfere with the link-editing being performed.

-I name
--dynamic-linker name
When building an executable, uses name as the path name of the
interpreter to be written into the program header. The default in
static mode is no interpreter. In dynamic mode, the default is the
name of the runtime linker, ld.so.1(1). Either case can be
overridden by -I name. exec(2) loads this interpreter when the a.out
is loaded, and passes control to the interpreter rather than to the
a.out directly.

-l x
--library x
Searches a library libx.so or libx.a, the conventional names for
shared object and archive libraries, respectively. In dynamic mode,
unless the -B static option is in effect, ld searches each directory
specified in the library search path for a libx.so or libx.a. The
directory search stops at the first directory containing either. ld
chooses the file ending in .so if -l x expands to two files with
names of the form libx.so and libx.a. If no libx.so is found, then
ld accepts libx.a. In static mode, or when the -B static option is
in effect, ld selects only the file ending in .a. ld searches a
library when the library is encountered, so the placement of -l is
significant. See Linking With Additional Libraries in Linker and
Libraries Guide.

-L path
--library-path path
Adds path to the library search directories. ld searches for
libraries first in any directories specified by the -L options and
then in the standard directories. This option is useful only if the
option precedes the -l options to which the -L option applies. See
Directories Searched by the Link-Editor in Linker and Libraries
Guide.

The environment variable LD_LIBRARY_PATH can be used to supplement
the library search path, however the -L option is recommended, as the
environment variable is also interpreted by the runtime environment.
See LD_LIBRARY_PATH under ENVIRONMENT.

-m Produces a memory map or listing of the input/output sections,
together with any non-fatal multiply-defined symbols, on the standard
output.

-M mapfile
Reads mapfile as a text file of directives to ld. This option can be
specified multiple times. If mapfile is a directory, then all
regular files, as defined by stat(2), within the directory are
processed. See Chapter 9, Mapfile Option, in Linker and Libraries
Guide. Example mapfiles are provided in /usr/lib/ld. See FILES.

-N string
This option causes a DT_NEEDED entry to be added to the .dynamic
section of the object being built. The value of the DT_NEEDED string
is the string that is specified on the command line. This option is
position dependent, and the DT_NEEDED .dynamic entry is relative to
the other dynamic dependencies discovered on the link-edit line.
This option is useful for specifying dependencies within device
driver relocatable objects when combined with the -d y and -r
options.

-o outfile
--output outfile
Produces an output object file that is named outfile. The name of
the default object file is a.out.

-p auditlib
Identifies an audit library, auditlib. This audit library is used to
audit the object being created at runtime. A shared object
identified as requiring auditing with the -p option, has this
requirement inherited by any object that specifies the shared object
as a dependency. See the -P option. See Runtime Linker Auditing
Interface in Linker and Libraries Guide.

-P auditlib
Identifies an audit library, auditlib. This audit library is used to
audit the dependencies of the object being created at runtime.
Dependency auditing can also be inherited from dependencies that are
identified as requiring auditing. See the -p and -z globalaudit
options. See Runtime Linker Auditing Interface in Linker and
Libraries Guide.

-Q y | -Q n
Under -Q y, an ident string is added to the .comment section of the
output file. This string identifies the version of the ld used to
create the file. This results in multiple ld idents when there have
been multiple linking steps, such as when using ld -r. This
identification is identical with the default action of the cc(1)
command. -Q n suppresses version identification. .comment sections
can be manipulated by the mcs(1) utility.

-r
--relocatable
Combines relocatable object files to produce one relocatable object
file. ld does not complain about unresolved references. This option
cannot be used with the -a option.

-R path
-rpath path
A colon-separated list of directories used to specify library search
directories to the runtime linker. If present and not NULL, the path
is recorded in the output object file and passed to the runtime
linker. Multiple instances of this option are concatenated together
with each path separated by a colon. See Directories Searched by the
Runtime Linker in Linker and Libraries Guide.

The use of a runpath within an associated object is preferable to
setting global search paths such as through the LD_LIBRARY_PATH
environment variable. Only the runpaths that are necessary to find
the objects dependencies should be recorded. ldd(1) can also be used
to discover unused runpaths in dynamic objects, when used with the -U
option.

Various tokens can also be supplied with a runpath that provide a
flexible means of identifying system capabilities or an objects
location. See Appendix C, Establishing Dependencies with Dynamic
String Tokens, in Linker and Libraries Guide. The $ORIGIN token is
especially useful in allowing dynamic objects to be relocated to
different locations in the file system.

-s
--strip-all
Strips symbolic information from the output file. Any debugging
information, that is, .line, .debug*, and .stab* sections, and their
associated relocation entries are removed. Except for relocatable
files, a symbol table SHT_SYMTAB and its associated string table
section are not created in the output object file. The elimination
of a SHT_SYMTAB symbol table can reduce the .stab* debugging
information that is generated using the compiler driver's -g option.
See the -z redlocsym and -z noldynsym options.

-S supportlib
The shared object supportlib is loaded with ld and given information
regarding the linking process. Shared objects that are defined by
using the -S option can also be supplied using the SGS_SUPPORT
environment variable. See Link-Editor Support Interface in Linker
and Libraries Guide.

-t Turns off the warning for multiply-defined symbols that have
different sizes or different alignments.

-u symname
--undefined symname
Enters symname as an undefined symbol in the symbol table. This
option is useful for loading entirely from an archive library. In
this instance, an unresolved reference is needed to force the loading
of the first routine. The placement of this option on the command
line is significant. This option must be placed before the library
that defines the symbol. See Defining Additional Symbols with the u
option in Linker and Libraries Guide.

-V
--version
Outputs a message giving information about the version of ld being
used.

-Y P,dirlist
Changes the default directories used for finding libraries. dirlist
is a colon-separated path list.

-z absexec
Useful only when building a dynamic executable. Specifies that
references to external absolute symbols should be resolved
immediately instead of being left for resolution at runtime. In very
specialized circumstances, this option removes text relocations that
can result in excessive swap space demands by an executable.

-z allextract | -z defaultextract | -z weakextract
--whole-archive | --no-whole-archive
Alters the extraction criteria of objects from any archives that
follow. By default, archive members are extracted to satisfy
undefined references and to promote tentative definitions with data
definitions. Weak symbol references do not trigger extraction.
Under the -z allextract or --whole-archive options, all archive
members are extracted from the archive. Under -z weakextract, weak
references trigger archive extraction. The -z defaultextract or
--no-whole-archive options provide a means of returning to the
default following use of the former extract options. See Archive
Processing in Linker and Libraries Guide.

-z altexec64
Execute the 64-bit ld. The creation of very large 32-bit objects can
exhaust the virtual memory that is available to the 32-bit ld. The
-z altexec64 option can be used to force the use of the associated
64-bit ld. The 64-bit ld provides a larger virtual address space for
building 32-bit objects. See The 32-bit link-editor and 64-bit
link-editor in Linker and Libraries Guide.

-z aslr[=state]
Specify whether the executable's address space should be randomized
on execution. If state is enabled, randomization will always occur
when this executable is run (regardless of inherited settings). If
state is disabled, randomization will never occur when this
executable is run. If state is omitted, ASLR is enabled. An
executable that should simply use the settings inherited from its
environment should not use this flag at all.

-z combreloc | -z nocombreloc
By default, ld combines multiple relocation sections when building
executables or shared objects. This section combination differs from
relocatable objects, in which relocation sections are maintained in a
one-to-one relationship with the sections to which the relocations
must be applied. The -z nocombreloc option disables this merging of
relocation sections, and preserves the one-to-one relationship found
in the original relocatable objects.

ld sorts the entries of data relocation sections by their symbol
reference. This sorting reduces runtime symbol lookup. When
multiple relocation sections are combined, this sorting produces the
least possible relocation overhead when objects are loaded into
memory, and speeds the runtime loading of dynamic objects.

Historically, the individual relocation sections were carried over to
any executable or shared object, and the -z combreloc option was
required to enable the relocation section merging previously
described. Relocation section merging is now the default. The -z
combreloc option is still accepted for the benefit of old build
environments, but the option is unnecessary, and has no effect.

-z assert-deflib
-z assert-deflib=libname
Enables warnings that check the location of where libraries passed in
with -l are found. If the link-editor finds a library on its default
search path it will emit a warning. This warning can be made fatal
in conjunction with the option -z fatal-warnings. Passing libname
white lists a library from this check. The library must be the full
name of the library, e.g. libc.so. To white list multiple
libraries, the -z assert-deflib=libname option can be repeated
multiple times. This option is useful when trying to build self-
contained objects where a referenced library might exist in the
default system library path and in alternate paths specified by -L,
but you only want the alternate paths to be used.

-z defs | -z nodefs
--no-undefined
The -z defs option and the --no-undefined option force a fatal error
if any undefined symbols remain at the end of the link. This mode is
the default when an executable is built. For historic reasons, this
mode is not the default when building a shared object. Use of the -z
defs option is recommended, as this mode assures the object being
built is self-contained. A self-contained object has all symbolic
references resolved internally, or to the object's immediate
dependencies.

The -z nodefs option allows undefined symbols. For historic reasons,
this mode is the default when a shared object is built. When used
with executables, the behavior of references to such undefined
symbols is unspecified. Use of the -z nodefs option is not
recommended.

-z direct | -z nodirect
Enables or disables direct binding to any dependencies that follow on
the command line. These options allow finer control over direct
binding than the global counterpart -B direct. The -z direct option
also differs from the -B direct option in the following areas.
Direct binding information is not established between a symbol
reference and an associated definition within the object being
created. Lazy loading is not enabled.

-z endfiltee
Marks a filtee so that when processed by a filter, the filtee
terminates any further filtee searches by the filter. See Reducing
Filtee Searches in Linker and Libraries Guide.

-z fatal-warnings | -z nofatal-warnings
--fatal-warnings | --no-fatal-warnings
Controls the behavior of warnings emitted from the link-editor.
Setting -z fatal-warnings promotes warnings emitted by the link-
editor to fatal errors that will cause the link-editor to fail before
linking. -z nofatal-warnings instead demotes these warnings such
that they will not cause the link-editor to exit prematurely.

-z finiarray=function
Appends an entry to the .fini_array section of the object being
built. If no .fini_array section is present, a section is created.
The new entry is initialized to point to function. See
Initialization and Termination Sections in Linker and Libraries
Guide.

-z globalaudit
This option supplements an audit library definition that has been
recorded with the -P option. This option is only meaningful when
building a dynamic executable. Audit libraries that are defined
within an object with the -P option typically allow for the auditing
of the immediate dependencies of the object. The -z globalaudit
promotes the auditor to a global auditor, thus allowing the auditing
of all dependencies. See Invoking the Auditing Interface in Linker
and Libraries Guide.

An auditor established with the -P option and the -z globalaudit
option, is equivalent to the auditor being established with the
LD_AUDIT environment variable. See ld.so.1(1).

-z groupperm | -z nogroupperm
Assigns, or deassigns each dependency that follows to a unique group.
The assignment of a dependency to a group has the same effect as if
the dependency had been built using the -B group option.

-z guidance[=id,...]
Give messages suggesting link-editor features that could improve the
resulting dynamic object. Specific classes of suggestion can be
silenced by specifying an optional comma separated list of guidance
identifiers. The current classes of suggestion provided are:

Enable use of direct binding
Suggests that -z direct or -B direct be present prior to any
specified dependency. This allows predictable symbol binding
at runtime. Can be disabled with -z guidance=nodirect

Enable lazy dependency loading
Suggests that -z lazyload be present prior to any specified
dependency. This allows the dynamic object to be loaded more
quickly. Can be disabled with -z guidance=nolazyload

Shared objects should define all their dependencies.
Suggests that -z defs be specified on the link-editor command
line. Shared objects that explicitly state all their
dependencies behave more predictably when used. Can be be
disabled with -z guidance=nodefs

Version 2 mapfile syntax
Suggests that any specified mapfiles use the more readable
version 2 syntax. Can be disabled with -z guidance=nomapfile

Read-only text segment
Should any runtime relocations within the text segment exist,
suggests that the object be compiled with position independent
code (PIC). Keeping large allocatable sections read-only
allows them to be shared between processes using a given shared
object. Can be disabled with -z guidance=notext

unused dependencies
Suggests that any dependency not referenced by the resulting
dynamic object be removed from the link-editor command line.
Can be disabled with -z guidance=nounused

Global data in shared libraries built with mapfiles have size
assertions
Suggests that any global data in a library built with a mapfile
asserts the size of that global data for ABI stability
purposes. Can be disabled with -z guidance=noasserts

-z help
--help
Print a summary of the command line options on the standard output
and exit.

-z ignore | -z record
Ignores, or records, dynamic dependencies that are not referenced as
part of the link-edit. Ignores, or records, unreferenced ELF
sections from the relocatable objects that are read as part of the
link-edit. By default, -z record is in effect.

If an ELF section is ignored, the section is eliminated from the
output file being generated. A section is ignored when three
conditions are true. The eliminated section must contribute to an
allocatable segment. The eliminated section must provide no global
symbols. No other section from any object that contributes to the
link-edit, must reference an eliminated section.

-z initarray=function
Appends an entry to the .init_array section of the object being
built. If no .init_array section is present, a section is created.
The new entry is initialized to point to function. See
Initialization and Termination Sections in Linker and Libraries
Guide.

-z initfirst
Marks the object so that its runtime initialization occurs before the
runtime initialization of any other objects brought into the process
at the same time. In addition, the object runtime finalization
occurs after the runtime finalization of any other objects removed
from the process at the same time. This option is only meaningful
when building a shared object.

-z interpose
Marks the object as an interposer. At runtime, an object is
identified as an explicit interposer if the object has been tagged
using the -z interpose option. An explicit interposer is also
established when an object is loaded using the LD_PRELOAD environment
variable. Implicit interposition can occur because of the load order
of objects, however, this implicit interposition is unknown to the
runtime linker. Explicit interposition can ensure that interposition
takes place regardless of the order in which objects are loaded.
Explicit interposition also ensures that the runtime linker searches
for symbols in any explicit interposers when direct bindings are in
effect.

-z lazyload | -z nolazyload
Enables or disables the marking of dynamic dependencies to be lazily
loaded. Dynamic dependencies which are marked Cm lazyload are not
loaded at initial process start-up. These dependencies are delayed
until the first binding to the object is made. Note: Lazy loading
requires the correct declaration of dependencies, together with
associated runpaths for each dynamic object used within a process.
See Lazy Loading of Dynamic Dependencies in Linker and Libraries
Guide.

-z ld32=arg,...
-z ld64=arg,...
The class of the link-editor is affected by the class of the output
file being created and by the capabilities of the underlying
operating system. The -z ld32 | -z ld64 options provide a means of
defining any link-editor argument. The defined argument is only
interpreted, respectively, by the 32-bit class or 64-bit class of the
link-editor.

For example, support libraries are class specific, so the correct
class of support library can be ensured using:

ld ... -z ld32=-Saudit32.so.1 -z ld64=-Saudit64.so.1 ...

The class of link-editor that is invoked is determined from the ELF
class of the first relocatable file that is seen on the command line.
This determination is carried out prior to any -z ld32 | -z ld64
processing.

-z loadfltr
Marks a filter to indicate that filtees must be processed immediately
at runtime. Normally, filter processing is delayed until a symbol
reference is bound to the filter. The runtime processing of an
object that contains this flag mimics that which occurs if the
LD_LOADFLTR environment variable is in effect. See the ld.so.1(1).

-z muldefs
--allow-multiple-definition
Allows multiple symbol definitions. By default, multiple symbol
definitions that occur between relocatable objects result in a fatal
error condition. This option, suppresses the error condition,
allowing the first symbol definition to be taken.

-z nocompstrtab
Disables the compression of ELF string tables. By default, string
compression is applied to SHT_STRTAB sections, and to SHT_PROGBITS
sections that have their SHF_MERGE and SHF_STRINGS section flags set.

-z nodefaultlib
Marks the object so that the runtime default library search path,
used after any LD_LIBRARY_PATH or runpaths, is ignored. This option
implies that all dependencies of the object can be satisfied from its
runpath.

-z nodelete
Marks the object as non-deletable at runtime. This mode is similar
to adding the object to the process by using dlopen(3C) with the
RTLD_NODELETE mode.

-z nodlopen
Marks the object as not available to dlopen(3C), either as the object
specified by the dlopen(3C), or as any form of dependency required by
the object specified by the dlopen(3C). This option is only
meaningful when building a shared object.

-z nodump
Marks the object as not available to dldump(3C).

-z noldynsym
Prevents the inclusion of a .SUNW_ldynsym section in dynamic
executables or sharable libraries. The .SUNW_ldynsym section
augments the .dynsym section by providing symbols for local
functions. Local function symbols allow debuggers to display local
function names in stack traces from stripped programs. Similarly,
dladdr(3C) is able to supply more accurate results.

The -z noldynsym option also prevents the inclusion of the two symbol
sort sections that are related to the .SUNW_ldynsym section. The
.SUNW_dynsymsort section provides sorted access to regular function
and variable symbols. The .SUNW_dyntlssort section provides sorted
access to thread local storage (TLS) variable symbols.

The .SUNW_ldynsym, .SUNW_dynsymsort, and .SUNW_dyntlssort sections,
which becomes part of the allocable text segment of the resulting
file, cannot be removed by strip(1). Therefore, the -z noldynsym
option is the only way to prevent their inclusion. See the -s and -z
redlocsym options.

-z nopartial
Partially initialized symbols, that are defined within relocatable
object files, are expanded in the output file being generated.

-z noversion
Does not record any versioning sections. Any version sections or
associated .dynamic section entries are not generated in the output
image.

-z now
Marks the object as requiring non-lazy runtime binding. This mode is
similar to adding the object to the process by using dlopen(3C) with
the RTLD_NOW mode. This mode is also similar to having the
LD_BIND_NOW environment variable in effect. See ld.so.1(1).

-z origin
Marks the object as requiring immediate $ORIGIN processing at
runtime. This option is only maintained for historic compatibility,
as the runtime analysis of objects to provide for $ORIGIN processing
is now default.

-z preinitarray=function
Appends an entry to the .preinitarray section of the object being
built. If no .preinitarray section is present, a section is created.
The new entry is initialized to point to function. See
Initialization and Termination Sections in Linker and Libraries
Guide.

-z redlocsym
Eliminates all local symbols except for the SECT symbols from the
symbol table SHT_SYMTAB. All relocations that refer to local symbols
are updated to refer to the corresponding SECT symbol. This option
allows specialized objects to greatly reduce their symbol table
sizes. Eliminated local symbols can reduce the .stab debugging
information that is generated using the compiler driver's -g option.
See the -s and -z noldynsym options.

-z relaxreloc
ld normally issues a fatal error upon encountering a relocation using
a symbol that references an eliminated COMDAT section. If -z
relaxreloc is enabled, ld instead redirects such relocations to the
equivalent symbol in the COMDAT section that was kept. -z relaxreloc
is a specialized option, mainly of interest to compiler authors, and
is not intended for general use.

-z rescan-now
-z rescan
These options rescan the archive files that are provided to the link-
edit. By default, archives are processed once as the archives appear
on the command line. Archives are traditionally specified at the end
of the command line so that their symbol definitions resolve any
preceding references. However, specifying archives multiple times to
satisfy their own interdependencies can be necessary.

-z rescan-now is a positional option, and is processed by the link-
editor immediately when encountered on the command line. All
archives seen on the command line up to that point are immediately
reprocessed in an attempt to locate additional archive members that
resolve symbol references. This archive rescanning is repeated until
a pass over the archives occurs in which no new members are
extracted.

-z rescan is a position independent option. The link-editor defers
the rescan operation until after it has processed the entire command
line, and then initiates a final rescan operation over all archives
seen on the command line. The -z rescan operation can interact
incorrectly with objects that contain initialization (.init) or
finalization (.fini) sections, preventing the code in those sections
from running. For this reason, -z rescan is deprecated, and use of
-z rescan-now is advised.

-z rescan-start ... -z rescan-end
--start-group ... --end-group
-( ... -)
Defines an archive rescan group. This is a positional construct, and
is processed by the link-editor immediately upon encountering the
closing delimiter option. Archives found within the group delimiter
options are reprocessed as a group in an attempt to locate additional
archive members that resolve symbol references. This archive
rescanning is repeated until a pass over the archives occurs in which
no new members are extracted. Archive rescan groups cannot be
nested.

-z symbolcap
Specifies that a relocatable object that defines object capabilities
should have those converted to symbol capabilities. A relocatable
object that does not have any object capabilities will ignore this
option.

Symbol capabilities provide a means for multiple implementations of a
function to co-exist and have one picked at runtime based upon the
hardware capabilities of the system. When -z symbolcap is invoked,
all global functions are converted into local functions that have the
corresponding capability name appended to them and an undefined
symbol with the original name left in the resulting relocatable
object. At runtime, the global symbol will be bound to the
corresponding implementation that is appropriate based on the
capabilities of the system.

-z target=sparc|x86
Specifies the machine type for the output object. Supported targets
are sparc and x86. The 32-bit machine type for the specified target
is used unless the -64 option is also present, in which case the
corresponding 64-bit machine type is used. By default, the machine
type of the object being generated is determined from the first ELF
object processed from the command line. If no objects are specified,
the machine type is determined by the first object encountered within
the first archive processed from the command line. If there are no
objects or archives, the link-editor assumes the native machine.
This option is useful when creating an object directly with ld whose
input is solely from a mapfile. See the -M option. It can also be
useful in the rare case of linking entirely from an archive that
contains objects of different machine types for which the first
object is not of the desired machine type. See The 32-bit
link-editor and 64-bit link-editor in Linker and Libraries Guide.

Note that for compatibility with existing Makefiles and scripts,
these options may be given multiple times and may be mixed in the
same invocation: the last instance wins, so that, for example, `ld -z
target=sparc -z target=x86 ...' gives a machine type of `x86'.

-z text
In dynamic mode only, forces a fatal error if any relocations against
non-writable, allocatable sections remain. For historic reasons,
this mode is not the default when building an executable or shared
object. However, its use is recommended to ensure that the text
segment of the dynamic object being built is shareable between
multiple running processes. A shared text segment incurs the least
relocation overhead when loaded into memory. See
Position-Independent Code in Linker and Libraries Guide.

-z textoff
In dynamic mode only, allows relocations against all allocatable
sections, including non-writable ones. This mode is the default when
building a shared object.

-z textwarn
In dynamic mode only, lists a warning if any relocations against non-
writable, allocatable sections remain. This mode is the default when
building an executable.

-z type=exec|kmod|reloc|shared
Specifies the type of object to create.

exec Dynamic executable

reloc Relocatable object

shared Dynamic shared object

kmod illumos kernel module

-z verbose
This option provides additional warning diagnostics during a link-
edit. Presently, this option conveys suspicious use of displacement
relocations. This option also conveys the restricted use of static
TLS relocations when building shared objects. In future, this option
might be enhanced to provide additional diagnostics that are deemed
too noisy to be generated by default.

-z wrap=symbol
-wrap=symbol
--wrap=symbol
Rename undefined references to symbol in order to allow wrapper code
to be linked into the output object without having to modify source
code. When -z wrap is specified, all undefined references to symbol
are modified to reference __wrap_symbol, and all references to
__real_symbol are modified to reference symbol. The user is expected
to provide an object containing the __wrap_symbol function. This
wrapper function can call __real_symbol in order to reference the
actual function being wrapped.

The following is an example of a wrapper for the malloc(3C) function:

void *
__wrap_malloc(size_t c)
{
(void) printf("malloc called with %zu\n", c);
return (__real_malloc(c));
}

If you link other code with this file using -z wrap=malloc to compile
all the objects, then all calls to malloc will call the function
__wrap_malloc instead. The call to __real_malloc will call the real
malloc function.

The real and wrapped functions should be maintained in separate
source files. Otherwise, the compiler or assembler may resolve the
call instead of leaving that operation for the link-editor to carry
out, and prevent the wrap from occurring.

ENVIRONMENT


LD_ALTEXEC
An alternative link-editor path name. ld executes, and passes
control to this alternative link-editor. This environment variable
provides a generic means of overriding the default link-editor that
is called from the various compiler drivers. See the -z altexec64
option.

LD_LIBRARY_PATH
A list of directories in which to search for the libraries specified
using the -l option. Multiple directories are separated by a colon.
In the most general case, this environment variable contains two
directory lists separated by a semicolon:

dirlist1;dirlist2

If ld is called with any number of occurrences of -L, as in:

ld ... -Lpath1 ... -Lpathn ...

then the search path ordering is:

dirlist1 path1 ... pathn dirlist2 LIBPATH

When the list of directories does not contain a semicolon, the list
is interpreted as dirlist2.

The LD_LIBRARY_PATH environment variable also affects the runtime
linkers search for dynamic dependencies.

This environment variable can be specified with a _32 or _64 suffix.
This makes the environment variable specific, respectively, to 32-bit
or 64-bit processes and overrides any non-suffixed version of the
environment variable that is in effect.

LD_NOEXEC_64
Suppresses the automatic execution of the 64-bit link-editor. By
default, the link-editor executes the 64-bit version when the ELF
class of the first relocatable file identifies a 64-bit object. The
64-bit image that a 32-bit link-editor can create, has some
limitations. However, some link-edits might find the use of the
32-bit link-editor faster.

LD_OPTIONS
A default set of options to ld. LD_OPTIONS is interpreted by ld just
as though its value had been placed on the command line, immediately
following the name used to invoke ld, as in:

ld $LD_OPTIONS ... other-arguments ...

LD_RUN_PATH
An alternative mechanism for specifying a runpath to the link-editor.
See the -R option. If both LD_RUN_PATH and the -R option are
specified, -R supersedes.

SGS_SUPPORT
Provides a colon-separated list of shared objects that are loaded
with the link-editor and given information regarding the linking
process. This environment variable can be specified with a _32 or
_64 suffix. This makes the environment variable specific,
respectively, to the 32-bit or 64-bit class of ld and overrides any
non-suffixed version of the environment variable that is in effect.
See the -S option.

Notice that environment variable-names that begin with the characters `LD_'
are reserved for possible future enhancements to ld and ld.so.1(1).

FILES


libx.so
shared object libraries.

libx.a
archive libraries.

a.out
default output file.

LIBPATH
For 32-bit libraries, the default search path is /usr/ccs/lib,
followed by /lib, and finally /usr/lib. For 64-bit libraries, the
default search path is /lib/64, followed by /usr/lib/64.

/usr/lib/ld
A directory containing several mapfiles that can be used during link-
editing. These mapfiles provide various capabilities, such as
defining memory layouts, aligning bss, and defining non-executable
stacks.

ATTRIBUTES


The command line interface of ld is Committed. The output of ld is
Committed.

SEE ALSO


as(1), crle(1), gprof(1), ld.so.1(1), ldd(1), mcs(1), pvs(1), strip(1),
exec(2), stat(2), dladdr(3C), dldump(3C), dlopen(3C), malloc(3C),
elf(3ELF), ar.h(3HEAD), a.out(5), attributes(7)

Linker and Libraries Guide.

NOTES


Default options applied by ld are maintained for historic reasons. In
today's programming environment, where dynamic objects dominate,
alternative defaults would often make more sense. However, historic
defaults must be maintained to ensure compatibility with existing program
development environments. Historic defaults are called out wherever
possible in this manual. For a description of the current recommended
options, see Appendix A, Link-Editor Quick Reference, in Linker and
Libraries Guide.

If the file being created by ld already exists, the file is unlinked after
all input files have been processed. A new file with the specified name is
then created. This allows ld to create a new version of the file, while
simultaneously allowing existing processes that are accessing the old file
contents to continue running. If the old file has no other links, the disk
space of the removed file is freed when the last process referencing the
file terminates.

The behavior of ld when the file being created already exists was changed
with SXCE build 43. In older versions, the existing file was rewritten in
place, an approach with the potential to corrupt any running processes that
is using the file. This change has an implication for output files that
have multiple hard links in the file system. Previously, all links would
remain intact, with all links accessing the new file contents. The new ld
behavior breaks such links, with the result that only the specified output
file name references the new file. All the other links continue to
reference the old file. To ensure consistent behavior, applications that
rely on multiple hard links to linker output files should explicitly remove
and relink the other file names.

illumos January 15, 2024 illumos