\input texinfo
@setfilename ld.info
-@c Copyright 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
-@c 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011,
-@c 2012, 2013
-@c Free Software Foundation, Inc.
+@c Copyright (C) 1991-2016 Free Software Foundation, Inc.
@syncodeindex ky cp
@c man begin INCLUDE
@include configdoc.texi
@set I960
@set M68HC11
@set M68K
+@set MIPS
@set MMIX
@set MSP430
+@set NDS32
+@set NIOSII
@set POWERPC
@set POWERPC64
@set Renesas
@end ifset
version @value{VERSION}.
-Copyright @copyright{} 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
-2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012, 2013
-Free Software Foundation, Inc.
+Copyright @copyright{} 1991-2016 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
@vskip 0pt plus 1filll
@c man begin COPYRIGHT
-Copyright @copyright{} 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
-1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
-2012, 2013 Free Software Foundation, Inc.
+Copyright @copyright{} 1991-2016 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
@ifset M68K
* M68K:: ld and Motorola 68K family
@end ifset
+@ifset MIPS
+* MIPS:: ld and MIPS family
+@end ifset
@ifset POWERPC
* PowerPC ELF32:: ld and PowerPC 32-bit ELF Support
@end ifset
@itemx --gpsize=@var{value}
Set the maximum size of objects to be optimized using the GP register to
@var{size}. This is only meaningful for object file formats such as
-MIPS ECOFF which supports putting large and small objects into different
+MIPS ELF that support putting large and small objects into different
sections. This is ignored for other object file formats.
@cindex runtime library name
option is specified.
If @var{searchdir} begins with @code{=}, then the @code{=} will be replaced
-by the @dfn{sysroot prefix}, a path specified when the linker is configured.
+by the @dfn{sysroot prefix}, controlled by the @samp{--sysroot} option, or
+specified when the linker is configured.
@ifset UsesEnvVars
The default set of paths searched (without being specified with
no difference in the linker's behaviour for different non-zero values
of this option. Again this may change with future releases.
+@kindex --push-state
+@cindex push state governing input file handling
+@item --push-state
+The @option{--push-state} allows to preserve the current state of the
+flags which govern the input file handling so that they can all be
+restored with one corresponding @option{--pop-state} option.
+
+The option which are covered are: @option{-Bdynamic}, @option{-Bstatic},
+@option{-dn}, @option{-dy}, @option{-call_shared}, @option{-non_shared},
+@option{-static}, @option{-N}, @option{-n}, @option{--whole-archive},
+@option{--no-whole-archive}, @option{-r}, @option{-Ur},
+@option{--copy-dt-needed-entries}, @option{--no-copy-dt-needed-entries},
+@option{--as-needed}, @option{--no-as-needed}, and @option{-a}.
+
+One target for this option are specifications for @file{pkg-config}. When
+used with the @option{--libs} option all possibly needed libraries are
+listed and then possibly linked with all the time. It is better to return
+something as follows:
+
+@smallexample
+-Wl,--push-state,--as-needed -libone -libtwo -Wl,--pop-state
+@end smallexample
+
+@kindex --pop-state
+@cindex pop state governing input file handling
+Undoes the effect of --push-state, restores the previous values of the
+flags governing input file handling.
+
@kindex -q
@kindex --emit-relocs
@cindex retain relocations in final executable
different option arguments to enter additional undefined symbols. This
option is equivalent to the @code{EXTERN} linker script command.
+If this option is being used to force additional modules to be pulled
+into the link, and if it is an error for the symbol to remain
+undefined, then the option @option{--require-defined} should be used
+instead.
+
+@kindex --require-defined=@var{symbol}
+@cindex symbols, require defined
+@cindex defined symbol
+@item --require-defined=@var{symbol}
+Require that @var{symbol} is defined in the output file. This option
+is the same as option @option{--undefined} except that if @var{symbol}
+is not defined in the output file then the linker will issue an error
+and exit. The same effect can be achieved in a linker script by using
+@code{EXTERN}, @code{ASSERT} and @code{DEFINED} together. This option
+can be used multiple times to require additional symbols.
+
@kindex -Ur
@cindex constructors
@item -Ur
be added to. Use @samp{-Ur} only for the last partial link, and
@samp{-r} for the others.
+@kindex --orphan-handling=@var{MODE}
+@cindex orphan sections
+@cindex sections, orphan
+@item --orphan-handling=@var{MODE}
+Control how orphan sections are handled. An orphan section is one not
+specifically mentioned in a linker script. @xref{Orphan Sections}.
+
+@var{MODE} can have any of the following values:
+
+@table @code
+@item place
+Orphan sections are placed into a suitable output section following
+the strategy described in @ref{Orphan Sections}. The option
+@samp{--unique} also effects how sections are placed.
+
+@item discard
+All orphan sections are discarded, by placing them in the
+@samp{/DISCARD/} section (@pxref{Output Section Discarding}).
+
+@item warn
+The linker will place the orphan section as for @code{place} and also
+issue a warning.
+
+@item error
+The linker will exit with an error if any orphan section is found.
+@end table
+
+The default if @samp{--orphan-handling} is not given is @code{place}.
+
@kindex --unique[=@var{SECTION}]
@item --unique[=@var{SECTION}]
Creates a separate output section for every input section matching
Combines multiple reloc sections and sorts them to make dynamic symbol
lookup caching possible.
+@item common
+Generate common symbols with the STT_COMMON type druing a relocatable
+link.
+
@item defs
Disallows undefined symbols in object files. Undefined symbols in
shared libraries are still allowed.
@item nocombreloc
Disables multiple reloc sections combining.
+@item nocommon
+Generate common symbols with the STT_OBJECT type druing a relocatable
+link.
+
@item nocopyreloc
-Disables production of copy relocs.
+Disable linker generated .dynbss variables used in place of variables
+defined in shared libraries. May result in dynamic text relocations.
@item nodefaultlib
Marks the object that the search for dependencies of this object will
@item noexecstack
Marks the object as not requiring executable stack.
+@item text
+Treat DT_TEXTREL in shared object as error.
+
+@item notext
+Don't treat DT_TEXTREL in shared object as error.
+
+@item textoff
+Don't treat DT_TEXTREL in shared object as error.
+
@item norelro
Don't create an ELF @code{PT_GNU_RELRO} segment header in the object.
Specifying zero will override any default non-zero sized
@code{PT_GNU_STACK} segment creation.
+@item bndplt
+Always generate BND prefix in PLT entries. Supported for Linux/x86_64.
+
+@item noextern-protected-data
+Don't treat protected data symbol as external when building shared
+library. This option overrides linker backend default. It can be used
+to workaround incorrect relocations against protected data symbols
+generated by compiler. Updates on protected data symbols by another
+module aren't visible to the resulting shared library. Supported for
+i386 and x86-64.
+
+@item nodynamic-undefined-weak
+Don't treat undefined weak symbols as dynamic when building executable.
+This option overrides linker backend default. It can be used to avoid
+dynamic relocations against undefined weak symbols in executable.
+Supported for i386 and x86-64.
+
+@item noreloc-overflow
+Disable relocation overflow check. This can be used to disable
+relocation overflow check if there will be no dynamic relocation
+overflow at run-time. Supported for x86_64.
+
+@item call-nop=prefix-addr
+@itemx call-nop=prefix-nop
+@itemx call-nop=suffix-nop
+@itemx call-nop=prefix-@var{byte}
+@itemx call-nop=suffix-@var{byte}
+Specify the 1-byte @code{NOP} padding when transforming indirect call
+to a locally defined function, foo, via its GOT slot.
+@option{call-nop=prefix-addr} generates @code{0x67 call foo}.
+@option{call-nop=prefix-nop} generates @code{0x90 call foo}.
+@option{call-nop=suffix-nop} generates @code{call foo 0x90}.
+@option{call-nop=prefix-@var{byte}} generates @code{@var{byte} call foo}.
+@option{call-nop=suffix-@var{byte}} generates @code{call foo @var{byte}}.
+Supported for i386 and x86_64.
+
@end table
Other keywords are ignored for Solaris compatibility.
the linker will add a DT_NEEDED tag for each dynamic library mentioned
on the command line, regardless of whether the library is actually
needed or not. @option{--as-needed} causes a DT_NEEDED tag to only be
-emitted for a library that satisfies an undefined symbol reference
-from a regular object file or, if the library is not found in the
-DT_NEEDED lists of other libraries linked up to that point, an
-undefined symbol reference from another dynamic library.
-@option{--no-as-needed} restores the default behaviour.
+emitted for a library that @emph{at that point in the link} satisfies a
+non-weak undefined symbol reference from a regular object file or, if
+the library is not found in the DT_NEEDED lists of other needed libraries, a
+non-weak undefined symbol reference from another needed dynamic library.
+Object files or libraries appearing on the command line @emph{after}
+the library in question do not affect whether the library is seen as
+needed. This is similar to the rules for extraction of object files
+from archives. @option{--no-as-needed} restores the default behaviour.
@kindex --add-needed
@kindex --no-add-needed
When creating a shared library, bind references to global symbols to the
definition within the shared library, if any. Normally, it is possible
for a program linked against a shared library to override the definition
-within the shared library. This option is only meaningful on ELF
-platforms which support shared libraries.
+within the shared library. This option can also be used with the
+@option{--export-dynamic} option, when creating a position independent
+executable, to bind references to global symbols to the definition within
+the executable. This option is only meaningful on ELF platforms which
+support shared libraries and position independent executables.
@kindex -Bsymbolic-functions
@item -Bsymbolic-functions
When creating a shared library, bind references to global function
symbols to the definition within the shared library, if any.
+This option can also be used with the @option{--export-dynamic} option,
+when creating a position independent executable, to bind references
+to global function symbols to the definition within the executable.
This option is only meaningful on ELF platforms which support shared
-libraries.
+libraries and position independent executables.
@kindex --dynamic-list=@var{dynamic-list-file}
@item --dynamic-list=@var{dynamic-list-file}
easily processed by a script if necessary. The symbols are printed out,
sorted by name. For each symbol, a list of file names is given. If the
symbol is defined, the first file listed is the location of the
-definition. The remaining files contain references to the symbol.
+definition. If the symbol is defined as a common value then any files
+where this happens appear next. Finally any files that reference the
+symbol are listed.
@cindex common allocation
@kindex --no-define-common
context: you may give a hexadecimal constant or the name of an existing
symbol, or use @code{+} and @code{-} to add or subtract hexadecimal
constants or symbols. If you need more elaborate expressions, consider
-using the linker command language from a script (@pxref{Assignments,,
-Assignment: Symbol Definitions}). @emph{Note:} there should be no white
-space between @var{symbol}, the equals sign (``@key{=}''), and
-@var{expression}.
+using the linker command language from a script (@pxref{Assignments}).
+@emph{Note:} there should be no white space between @var{symbol}, the
+equals sign (``@key{=}''), and @var{expression}.
@cindex demangling, from command line
@kindex --demangle[=@var{style}]
linker is normally correct; don't use this unless you know what you are
doing.
+@kindex --no-dynamic-linker
+@item --no-dynamic-linker
+When producing an executable file, omit the request for a dynamic
+linker to be used at load-time. This is only meaningful for ELF
+executables that contain dynamic relocations, and usually requires
+entry point code that is capable of processing these relocations.
+
@kindex --fatal-warnings
@kindex --no-fatal-warnings
@item --fatal-warnings
Enable garbage collection of unused input sections. It is ignored on
targets that do not support this option. The default behaviour (of not
performing this garbage collection) can be restored by specifying
-@samp{--no-gc-sections} on the command line.
+@samp{--no-gc-sections} on the command line. Note that garbage
+collection for COFF and PE format targets is supported, but the
+implementation is currently considered to be experimental.
@samp{--gc-sections} decides which input sections are used by
examining symbols and relocations. The section containing the entry
other command-line options). This is the string that would appear
in an @code{OUTPUT_FORMAT} linker script command (@pxref{File Commands}).
+@kindex --print-memory-usage
+@cindex memory usage
+@item --print-memory-usage
+Print used size, total size and used size of memory regions created with
+the @ref{MEMORY} command. This is useful on embedded targets to have a
+quick view of amount of free memory. The format of the output has one
+headline and one line per region. It is both human readable and easily
+parsable by tools. Here is an example of an output:
+
+@smallexample
+Memory region Used Size Region Size %age Used
+ ROM: 256 KB 1 MB 25.00%
+ RAM: 32 B 2 GB 0.00%
+@end smallexample
+
@cindex help
@cindex usage
@kindex --help
this option overrides it. @xref{BFD}.
@end ifclear
+@kindex --out-implib
+@item --out-implib @var{file}
+Create an import library in @var{file} corresponding to the executable
+the linker is generating (eg. a DLL or ELF program). This import
+library (which should be called @code{*.dll.a} or @code{*.a} for DLLs)
+may be used to link clients against the generated executable; this
+behaviour makes it possible to skip a separate import library creation
+step (eg. @code{dlltool} for DLLs). This option is only available for
+the i386 PE and ELF targetted ports of the linker.
+
@kindex -pie
@kindex --pic-executable
@item -pie
@ifset M68HC11
@xref{M68HC11/68HC12,,@command{ld} and the 68HC11 and 68HC12}.
@end ifset
+@ifset NIOSII
+@xref{Nios II,,@command{ld} and the Altera Nios II}.
+@end ifset
@ifset POWERPC
@xref{PowerPC ELF32,,@command{ld} and PowerPC 32-bit ELF Support}.
@end ifset
@code{LD_RUN_PATH} will be used if it is defined.
The @option{-rpath} option may also be used on SunOS. By default, on
-SunOS, the linker will form a runtime search patch out of all the
+SunOS, the linker will form a runtime search path out of all the
@option{-L} options it is given. If a @option{-rpath} option is used, the
runtime search path will be formed exclusively using the @option{-rpath}
options, ignoring the @option{-L} options. This can be useful when using
@kindex -Ttext-segment=@var{org}
@item -Ttext-segment=@var{org}
@cindex text segment origin, cmd line
-When creating an ELF executable or shared object, it will set the address
-of the first byte of the text segment.
+When creating an ELF executable, it will set the address of the first
+byte of the text segment.
@kindex -Trodata-segment=@var{org}
@item -Trodata-segment=@var{org}
the classic ELF @code{.hash} and new style GNU @code{.gnu.hash}
hash tables. The default is @code{sysv}.
+@kindex --compress-debug-sections=none
+@kindex --compress-debug-sections=zlib
+@kindex --compress-debug-sections=zlib-gnu
+@kindex --compress-debug-sections=zlib-gabi
+@item --compress-debug-sections=none
+@itemx --compress-debug-sections=zlib
+@itemx --compress-debug-sections=zlib-gnu
+@itemx --compress-debug-sections=zlib-gabi
+On ELF platforms , these options control how DWARF debug sections are
+compressed using zlib. @option{--compress-debug-sections=none} doesn't
+compress DWARF debug sections.
+@option{--compress-debug-sections=zlib-gnu} compresses DWARF debug
+sections and rename debug section names to begin with @samp{.zdebug}
+instead of @samp{.debug}. @option{--compress-debug-sections=zlib}
+and @option{--compress-debug-sections=zlib-gabi}
+compress DWARF debug sections with SHF_COMPRESSED from the ELF ABI.
+The default behaviour varies depending upon the target involved and
+the configure options used to build the toolchain. The default can be
+determined by examing the output from the linker's @option{--help} option.
+
@kindex --reduce-memory-overheads
@item --reduce-memory-overheads
This option reduces memory requirements at ld runtime, at the expense of
@kindex --build-id=@var{style}
@item --build-id
@itemx --build-id=@var{style}
-Request creation of @code{.note.gnu.build-id} ELF note section.
-The contents of the note are unique bits identifying this linked
-file. @var{style} can be @code{uuid} to use 128 random bits,
-@code{sha1} to use a 160-bit @sc{SHA1} hash on the normative
-parts of the output contents, @code{md5} to use a 128-bit
-@sc{MD5} hash on the normative parts of the output contents, or
-@code{0x@var{hexstring}} to use a chosen bit string specified as
-an even number of hexadecimal digits (@code{-} and @code{:}
-characters between digit pairs are ignored). If @var{style} is
-omitted, @code{sha1} is used.
+Request the creation of a @code{.note.gnu.build-id} ELF note section
+or a @code{.buildid} COFF section. The contents of the note are
+unique bits identifying this linked file. @var{style} can be
+@code{uuid} to use 128 random bits, @code{sha1} to use a 160-bit
+@sc{SHA1} hash on the normative parts of the output contents,
+@code{md5} to use a 128-bit @sc{MD5} hash on the normative parts of
+the output contents, or @code{0x@var{hexstring}} to use a chosen bit
+string specified as an even number of hexadecimal digits (@code{-} and
+@code{:} characters between digit pairs are ignored). If @var{style}
+is omitted, @code{sha1} is used.
The @code{md5} and @code{sha1} styles produces an identifier
that is always the same in an identical output file, but will be
@kindex --disable-long-section-names
@item --enable-long-section-names
@itemx --disable-long-section-names
-The PE variants of the Coff object format add an extension that permits
+The PE variants of the COFF object format add an extension that permits
the use of section names longer than eight characters, the normal limit
-for Coff. By default, these names are only allowed in object files, as
-fully-linked executable images do not carry the Coff string table required
+for COFF. By default, these names are only allowed in object files, as
+fully-linked executable images do not carry the COFF string table required
to support the longer names. As a GNU extension, it is possible to
allow their use in executable images as well, or to (probably pointlessly!)
disallow it in object files, by using these two options. Executable images
@item --heap @var{reserve}
@itemx --heap @var{reserve},@var{commit}
Specify the number of bytes of memory to reserve (and optionally commit)
-to be used as heap for this program. The default is 1Mb reserved, 4K
+to be used as heap for this program. The default is 1MB reserved, 4K
committed.
[This option is specific to the i386 PE targeted port of the linker]
section of the BOOT.INI. Otherwise, this bit has no effect.
[This option is specific to PE targeted ports of the linker]
+@kindex --disable-large-address-aware
+@item --disable-large-address-aware
+Reverts the effect of a previous @samp{--large-address-aware} option.
+This is useful if @samp{--large-address-aware} is always set by the compiler
+driver (e.g. Cygwin gcc) and the executable does not support virtual
+addresses greater than 2 gigabytes.
+[This option is specific to PE targeted ports of the linker]
+
@kindex --major-image-version
@item --major-image-version @var{value}
Sets the major number of the ``image version''. Defaults to 1.
[This option is specific to the i386 PE targeted port of the linker]
@cindex DLLs, creating
-@kindex --out-implib
-@item --out-implib @var{file}
-The linker will create the file @var{file} which will contain an
-import lib corresponding to the DLL the linker is generating. This
-import lib (which should be called @code{*.dll.a} or @code{*.a}
-may be used to link clients against the generated DLL; this behaviour
-makes it possible to skip a separate @code{dlltool} import library
-creation step.
-[This option is specific to the i386 PE targeted port of the linker]
-
@kindex --enable-auto-image-base
@item --enable-auto-image-base
-Automatically choose the image base for DLLs, unless one is specified
-using the @code{--image-base} argument. By using a hash generated
-from the dllname to create unique image bases for each DLL, in-memory
-collisions and relocations which can delay program execution are
-avoided.
+@itemx --enable-auto-image-base=@var{value}
+Automatically choose the image base for DLLs, optionally starting with base
+@var{value}, unless one is specified using the @code{--image-base} argument.
+By using a hash generated from the dllname to create unique image bases
+for each DLL, in-memory collisions and relocations which can delay program
+execution are avoided.
[This option is specific to the i386 PE targeted port of the linker]
@kindex --disable-auto-image-base
@kindex --disable-runtime-pseudo-reloc
@item --disable-runtime-pseudo-reloc
Do not create pseudo relocations for non-zero offset DATA imports from
-DLLs. This is the default.
+DLLs.
[This option is specific to the i386 PE targeted port of the linker]
@kindex --enable-extra-pe-debug
@item --stack @var{reserve}
@itemx --stack @var{reserve},@var{commit}
Specify the number of bytes of memory to reserve (and optionally commit)
-to be used as stack for this program. The default is 2Mb reserved, 4K
+to be used as stack for this program. The default is 2MB reserved, 4K
committed.
[This option is specific to the i386 PE targeted port of the linker]
of the PE file header:
[These options are specific to PE targeted ports of the linker]
+@kindex --high-entropy-va
+@item --high-entropy-va
+Image is compatible with 64-bit address space layout randomization
+(ASLR).
+
@kindex --dynamicbase
@item --dynamicbase
The image base address may be relocated using address space layout
@item --tsaware
The image is Terminal Server aware.
+@kindex --insert-timestamp
+@item --insert-timestamp
+@itemx --no-insert-timestamp
+Insert a real timestamp into the image. This is the default behaviour
+as it matches legacy code and it means that the image will work with
+other, proprietary tools. The problem with this default is that it
+will result in slightly different images being produced each time the
+same sources are linked. The option @option{--no-insert-timestamp}
+can be used to insert a zero value for the timestamp, this ensuring
+that binaries produced from identical sources will compare
+identically.
@end table
@c man end
@kindex --dsbt-size
@item --dsbt-size @var{size}
-This option sets the number of entires in the DSBT of the current executable
+This option sets the number of entries in the DSBT of the current executable
or shared library to @var{size}. The default is to create a table with 64
entries.
@c man end
@end ifset
+@ifset MIPS
+@subsection Options specific to MIPS targets
+
+@c man begin OPTIONS
+
+The following options are supported to control microMIPS instruction
+generation when linking for MIPS targets.
+
+@table @gcctabopt
+
+@kindex --insn32
+@item --insn32
+@kindex --no-insn32
+@itemx --no-insn32
+These options control the choice of microMIPS instructions used in code
+generated by the linker, such as that in the PLT or lazy binding stubs,
+or in relaxation. If @samp{--insn32} is used, then the linker only uses
+32-bit instruction encodings. By default or if @samp{--no-insn32} is
+used, all instruction encodings are used, including 16-bit ones where
+possible.
+
+@end table
+
+@c man end
+@end ifset
+
@ifset UsesEnvVars
@node Environment
@section Environment Variables
Each section in an object file has a name and a size. Most sections
also have an associated block of data, known as the @dfn{section
-contents}. A section may be marked as @dfn{loadable}, which mean that
+contents}. A section may be marked as @dfn{loadable}, which means that
the contents should be loaded into memory when the output file is run.
A section with no contents may be @dfn{allocatable}, which means that an
area in memory should be set aside, but nothing in particular should be
located inside the @dfn{sysroot prefix}, the filename will be looked
for in the @dfn{sysroot prefix}. Otherwise, the linker will try to
open the file in the current directory. If it is not found, the
-linker will search through the archive library search path. See the
+linker will search through the archive library search path.
+The @dfn{sysroot prefix} can also be forced by specifying @code{=}
+as the first character in the filename path. See also the
description of @samp{-L} in @ref{Options,,Command Line Options}.
If you use @samp{INPUT (-l@var{file})}, @command{ld} will transform the
Ensure that @var{exp} is non-zero. If it is zero, then exit the linker
with an error code, and print @var{message}.
+Note that assertions are checked before the final stages of linking
+take place. This means that expressions involving symbols PROVIDEd
+inside section definitions will fail if the user has not set values
+for those symbols. The only exception to this rule is PROVIDEd
+symbols that just reference dot. Thus an assertion like this:
+
+@smallexample
+ .stack :
+ @{
+ PROVIDE (__stack = .);
+ PROVIDE (__stack_size = 0x100);
+ ASSERT ((__stack > (_end + __stack_size)), "Error: No room left for the stack");
+ @}
+@end smallexample
+
+will fail if @code{__stack_size} is not defined elsewhere. Symbols
+PROVIDEd outside of section definitions are evaluated earlier, so they
+can be used inside ASSERTions. Thus:
+
+@smallexample
+ PROVIDE (__stack_size = 0x100);
+ .stack :
+ @{
+ PROVIDE (__stack = .);
+ ASSERT ((__stack > (_end + __stack_size)), "Error: No room left for the stack");
+ @}
+@end smallexample
+
+will work.
+
@item EXTERN(@var{symbol} @var{symbol} @dots{})
@kindex EXTERN
@cindex undefined symbol in linker script
@code{NOCROSSREFS} command uses output section names, not input section
names.
+@item NOCROSSREFS_TO(@var{tosection} @var{fromsection} @dots{})
+@kindex NOCROSSREFS_TO(@var{tosection} @var{fromsections})
+@cindex cross references
+This command may be used to tell @command{ld} to issue an error about any
+references to one section from a list of other sections.
+
+The @code{NOCROSSREFS} command is useful when ensuring that two or more
+output sections are entirely independent but there are situations where
+a one-way dependency is needed. For example, in a multi-core application
+there may be shared code that can be called from each core but for safety
+must never call back.
+
+The @code{NOCROSSREFS_TO} command takes a list of output section names.
+The first section can not be referenced from any of the other sections.
+If @command{ld} detects any references to the first section from any of
+the other sections, it reports an error and returns a non-zero exit
+status. Note that the @code{NOCROSSREFS_TO} command uses output section
+names, not input section names.
+
@ifclear SingleFormat
@item OUTPUT_ARCH(@var{bfdarch})
@kindex OUTPUT_ARCH(@var{bfdarch})
int foo = 1000;
@end smallexample
-creates a entry called @samp{foo} in the symbol table. This entry
+creates an entry called @samp{foo} in the symbol table. This entry
holds the address of an @samp{int} sized block of memory where the
number 1000 is initially stored.
int * a = & foo;
@end smallexample
-looks up the symbol @samp{foo} in the symbol table, gets it address
+looks up the symbol @samp{foo} in the symbol table, gets its address
and then copies this address into the block of memory associated with
the variable @samp{a}.
@smallexample
@group
start_of_ROM = .ROM;
- end_of_ROM = .ROM + sizeof (.ROM) - 1;
+ end_of_ROM = .ROM + sizeof (.ROM);
start_of_FLASH = .FLASH;
@end group
@end smallexample
@end smallexample
Note the use of the @samp{&} operators. These are correct.
+Alternatively the symbols can be treated as the names of vectors or
+arrays and then the code will again work as expected:
+
+@smallexample
+@group
+ extern char start_of_ROM[], end_of_ROM[], start_of_FLASH[];
+
+ memcpy (start_of_FLASH, start_of_ROM, end_of_ROM - start_of_ROM);
+@end group
+@end smallexample
+
+Note how using this method does not require the use of @samp{&}
+operators.
@node SECTIONS
@section SECTIONS Command
@group
@var{section} [@var{address}] [(@var{type})] :
[AT(@var{lma})]
- [ALIGN(@var{section_align})]
+ [ALIGN(@var{section_align}) | ALIGN_WITH_INPUT]
[SUBALIGN(@var{subsection_align})]
[@var{constraint}]
@{
@var{output-section-command}
@var{output-section-command}
@dots{}
- @} [>@var{region}] [AT>@var{lma_region}] [:@var{phdr} :@var{phdr} @dots{}] [=@var{fillexp}]
+ @} [>@var{region}] [AT>@var{lma_region}] [:@var{phdr} :@var{phdr} @dots{}] [=@var{fillexp}] [,]
@end group
@end smallexample
The whitespace around @var{section} is required, so that the section
name is unambiguous. The colon and the curly braces are also required.
+The comma at the end may be required if a @var{fillexp} is used and
+the next @var{sections-command} looks like a continuation of the expression.
The line breaks and other white space are optional.
Each @var{output-section-command} may be one of the following:
@cindex SORT_BY_ALIGNMENT
@code{SORT_BY_ALIGNMENT} is very similar to @code{SORT_BY_NAME}. The
difference is @code{SORT_BY_ALIGNMENT} will sort sections into
-ascending order by alignment before placing them in the output file.
+descending order by alignment before placing them in the output file.
+Larger alignments are placed before smaller alignments in order to
+reduce the amount of padding necessary.
@cindex SORT_BY_INIT_PRIORITY
@code{SORT_BY_INIT_PRIORITY} is very similar to @code{SORT_BY_NAME}. The
@enumerate
@item
@code{SORT_BY_NAME} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern)).
-It will sort the input sections by name first, then by alignment if 2
+It will sort the input sections by name first, then by alignment if two
sections have the same name.
@item
@code{SORT_BY_ALIGNMENT} (@code{SORT_BY_NAME} (wildcard section pattern)).
-It will sort the input sections by alignment first, then by name if 2
+It will sort the input sections by alignment first, then by name if two
sections have the same alignment.
@item
@code{SORT_BY_NAME} (@code{SORT_BY_NAME} (wildcard section pattern)) is
@cindex discarding sections
@cindex sections, discarding
@cindex removing sections
-The linker will not create output sections with no contents. This is
-for convenience when referring to input sections that may or may not
-be present in any of the input files. For example:
+The linker will not normally create output sections with no contents.
+This is for convenience when referring to input sections that may or
+may not be present in any of the input files. For example:
@smallexample
.foo : @{ *(.foo) @}
@end smallexample
will only create a @samp{.foo} section in the output file if there is a
@samp{.foo} section in at least one input file, and if the input
sections are not all empty. Other link script directives that allocate
-space in an output section will also create the output section.
+space in an output section will also create the output section. So
+too will assignments to dot even if the assignment does not create
+space, except for @samp{. = 0}, @samp{. = . + 0}, @samp{. = sym},
+@samp{. = . + sym} and @samp{. = ALIGN (. != 0, expr, 1)} when
+@samp{sym} is an absolute symbol of value 0 defined in the script.
+This allows you to force output of an empty section with @samp{. = .}.
The linker will ignore address assignments (@pxref{Output Section Address})
on discarded output sections, except when the linker script defines
@kindex ALIGN(@var{section_align})
@cindex forcing output section alignment
@cindex output section alignment
-You can increase an output section's alignment by using ALIGN.
+You can increase an output section's alignment by using ALIGN. As an
+alternative you can enforce that the difference between the VMA and LMA remains
+intact throughout this output section with the ALIGN_WITH_INPUT attribute.
@node Forced Input Alignment
@subsubsection Forced Input Alignment
@dots{}
@} [:@var{phdr}@dots{}] [=@var{fill}]
@dots{}
- @} [>@var{region}] [:@var{phdr}@dots{}] [=@var{fill}]
+ @} [>@var{region}] [:@var{phdr}@dots{}] [=@var{fill}] [,]
@end group
@end smallexample
except that no addresses and no memory regions may be defined for
sections within an @code{OVERLAY}.
+The comma at the end may be required if a @var{fill} is used and
+the next @var{sections-command} looks like a continuation of the expression.
+
The sections are all defined with the same starting address. The load
addresses of the sections are arranged such that they are consecutive in
memory starting at the load address used for the @code{OVERLAY} as a
and defaults to the start address; the start address is also optional,
and defaults to the current value of the location counter).
-If the @code{NOCROSSREFS} keyword is used, and there any references
-among the sections, the linker will report an error. Since the sections
-all run at the same address, it normally does not make sense for one
-section to refer directly to another. @xref{Miscellaneous Commands,
-NOCROSSREFS}.
+If the @code{NOCROSSREFS} keyword is used, and there are any
+references among the sections, the linker will report an error. Since
+the sections all run at the same address, it normally does not make
+sense for one section to refer directly to another.
+@xref{Miscellaneous Commands, NOCROSSREFS}.
For each section within the @code{OVERLAY}, the linker automatically
provides two symbols. The symbol @code{__load_start_@var{secname}} is
regions that become too full. The linker will not shuffle sections
around to fit into the available regions.
-A linker script may contain at most one use of the @code{MEMORY}
-command. However, you can define as many blocks of memory within it as
-you wish. The syntax is:
+A linker script may contain many uses of the @code{MEMORY} command,
+however, all memory blocks defined are treated as if they were
+specified inside a single @code{MEMORY} command. The syntax for
+@code{MEMORY} is:
@smallexample
@group
MEMORY
For ELF targets, the attribute of the section includes section type as
well as section flag.
+The command line options @samp{--orphan-handling} and @samp{--unique}
+(@pxref{Options,,Command Line Options}) can be used to control which
+output sections an orphan is placed in.
+
If an orphaned section's name is representable as a C identifier then
the linker will automatically @pxref{PROVIDE} two symbols:
__start_SECNAME and __stop_SECNAME, where SECNAME is the name of the
doesn't change the value of the location counter---it just does
arithmetic on it. The two operand @code{ALIGN} allows an arbitrary
expression to be aligned upwards (@code{ALIGN(@var{align})} is
-equivalent to @code{ALIGN(., @var{align})}).
+equivalent to @code{ALIGN(ABSOLUTE(.), @var{align})}).
Here is an example which aligns the output @code{.data} section to the
next @code{0x2000} byte boundary after the preceding section and sets a
@end smallexample
or
@smallexample
-(ALIGN(@var{maxpagesize}) + (. & (@var{maxpagesize} - @var{commonpagesize})))
+(ALIGN(@var{maxpagesize})
+ + ((. + @var{commonpagesize} - 1) & (@var{maxpagesize} - @var{commonpagesize})))
@end smallexample
@noindent
depending on whether the latter uses fewer @var{commonpagesize} sized pages
@item DATA_SEGMENT_RELRO_END(@var{offset}, @var{exp})
@kindex DATA_SEGMENT_RELRO_END(@var{offset}, @var{exp})
This defines the end of the @code{PT_GNU_RELRO} segment when
-@samp{-z relro} option is used. Second argument is returned.
+@samp{-z relro} option is used.
When @samp{-z relro} option is not present, @code{DATA_SEGMENT_RELRO_END}
does nothing, otherwise @code{DATA_SEGMENT_ALIGN} is padded so that
@var{exp} + @var{offset} is aligned to the most commonly used page
boundary for particular target. If present in the linker script,
it must always come in between @code{DATA_SEGMENT_ALIGN} and
-@code{DATA_SEGMENT_END}.
+@code{DATA_SEGMENT_END}. Evaluates to the second argument plus any
+padding needed at the end of the @code{PT_GNU_RELRO} segment due to
+section alignment.
@smallexample
. = DATA_SEGMENT_RELRO_END(24, .);
Return the absolute LMA of the named @var{section}. (@pxref{Output
Section LMA}).
+@item LOG2CEIL(@var{exp})
+@kindex LOG2CEIL(@var{exp})
+Return the binary logarithm of @var{exp} rounded towards infinity.
+@code{LOG2CEIL(0)} returns 0.
+
@kindex MAX
@item MAX(@var{exp1}, @var{exp2})
Returns the maximum of @var{exp1} and @var{exp2}.
@item SEGMENT_START(@var{segment}, @var{default})
@kindex SEGMENT_START(@var{segment}, @var{default})
Return the base address of the named @var{segment}. If an explicit
-value has been given for this segment (with a command-line @samp{-T}
-option) that value will be returned; otherwise the value will be
-@var{default}. At present, the @samp{-T} command-line option can only
-be used to set the base address for the ``text'', ``data'', and
+value has already been given for this segment (with a command-line
+@samp{-T} option) then that value will be returned otherwise the value
+will be @var{default}. At present, the @samp{-T} command-line option
+can only be used to set the base address for the ``text'', ``data'', and
``bss'' sections, but you can use @code{SEGMENT_START} with any segment
name.
@ifset M68K
* M68K:: @command{ld} and the Motorola 68K family
@end ifset
+@ifset MIPS
+* MIPS:: @command{ld} and the MIPS family
+@end ifset
@ifset MMIX
* MMIX:: @command{ld} and MMIX
@end ifset
@ifset MSP430
* MSP430:: @command{ld} and MSP430
@end ifset
+@ifset NDS32
+* NDS32:: @command{ld} and NDS32
+@end ifset
+@ifset NIOSII
+* Nios II:: @command{ld} and the Altera Nios II
+@end ifset
@ifset POWERPC
* PowerPC ELF32:: @command{ld} and PowerPC 32-bit ELF Support
@end ifset
@cindex synthesizing on H8/300
@item synthesizing instructions
-@c FIXME: specifically mov.b, or any mov instructions really?
+@c FIXME: specifically mov.b, or any mov instructions really? -> mov.b only, at least on H8, H8H, H8S
@command{ld} finds all @code{mov.b} instructions which use the
sixteen-bit absolute address form, but refer to the top
page of memory, and changes them to use the eight-bit address form.
@samp{mov.b @code{@@}@var{aa}:8} whenever the address @var{aa} is in the
top page of memory).
+@command{ld} finds all @code{mov} instructions which use the register
+indirect with 32-bit displacement addressing mode, but use a small
+displacement inside 16-bit displacement range, and changes them to use
+the 16-bit displacement form. (That is: the linker turns @samp{mov.b
+@code{@@}@var{d}:32,ERx} into @samp{mov.b @code{@@}@var{d}:16,ERx}
+whenever the displacement @var{d} is in the 16 bit signed integer
+range. Only implemented in ELF-format ld).
+
@item bit manipulation instructions
@command{ld} finds all bit manipulation instructions like @code{band, bclr,
biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, bxor}
target subroutine is a leaf routine (that is, the target subroutine does
not itself call any subroutines).
-@cindex Cortex-A8 erratum workaround
-@kindex --fix-cortex-a8
-@kindex --no-fix-cortex-a8
-The @samp{--fix-cortex-a8} switch enables a link-time workaround for an erratum in certain Cortex-A8 processors. The workaround is enabled by default if you are targeting the ARM v7-A architecture profile. It can be enabled otherwise by specifying @samp{--fix-cortex-a8}, or disabled unconditionally by specifying @samp{--no-fix-cortex-a8}.
-
-The erratum only affects Thumb-2 code. Please contact ARM for further details.
-
-@kindex --merge-exidx-entries
-@kindex --no-merge-exidx-entries
-The @samp{--no-merge-exidx-entries} switch disables the merging of adjacent exidx entries in debuginfo.
-
@ifclear GENERIC
@lowersections
@end ifclear
@cindex BE8
@kindex --be8
The @samp{--be8} switch instructs @command{ld} to generate BE8 format
-executables. This option is only valid when linking big-endian objects.
-The resulting image will contain big-endian data and little-endian code.
+executables. This option is only valid when linking big-endian
+objects - ie ones which have been assembled with the @option{-EB}
+option. The resulting image will contain big-endian data and
+little-endian code.
@cindex TARGET1
@kindex --target1-rel
Programmer Advice Notice'' available on the ARM documentation website at:
http://infocenter.arm.com/.
+@cindex STM32L4xx erratum workaround
+@kindex --fix-stm32l4xx-629360
+
+The @samp{--fix-stm32l4xx-629360} switch enables a link-time
+workaround for a bug in the bus matrix / memory controller for some of
+the STM32 Cortex-M4 based products (STM32L4xx). When accessing
+off-chip memory via the affected bus for bus reads of 9 words or more,
+the bus can generate corrupt data and/or abort. These are only
+core-initiated accesses (not DMA), and might affect any access:
+integer loads such as LDM, POP and floating-point loads such as VLDM,
+VPOP. Stores are not affected.
+
+The bug can be avoided by splitting memory accesses into the
+necessary chunks to keep bus reads below 8 words.
+
+The workaround is not enabled by default, this is equivalent to use
+@samp{--fix-stm32l4xx-629360=none}. If you know you are using buggy
+STM32L4xx hardware, you can enable the workaround by specifying the
+linker option @samp{--fix-stm32l4xx-629360}, or the equivalent
+@samp{--fix-stm32l4xx-629360=default}.
+
+If the workaround is enabled, instructions are scanned for
+potentially-troublesome sequences, and a veneer is created for each
+such sequence which may trigger the erratum. The veneer consists in a
+replacement sequence emulating the behaviour of the original one and a
+branch back to the subsequent instruction. The original instruction is
+then replaced with a branch to the veneer.
+
+The workaround does not always preserve the memory access order for
+the LDMDB instruction, when the instruction loads the PC.
+
+The workaround is not able to handle problematic instructions when
+they are in the middle of an IT block, since a branch is not allowed
+there. In that case, the linker reports a warning and no replacement
+occurs.
+
+The workaround is not able to replace problematic instructions with a
+PC-relative branch instruction if the @samp{.text} section is too
+large. In that case, when the branch that replaces the original code
+cannot be encoded, the linker reports a warning and no replacement
+occurs.
+
@cindex NO_ENUM_SIZE_WARNING
@kindex --no-enum-size-warning
The @option{--no-enum-size-warning} switch prevents the linker from
only, because it relies on object files properties not present
otherwise.
+@cindex Cortex-A8 erratum workaround
+@kindex --fix-cortex-a8
+@kindex --no-fix-cortex-a8
+The @samp{--fix-cortex-a8} switch enables a link-time workaround for an erratum in certain Cortex-A8 processors. The workaround is enabled by default if you are targeting the ARM v7-A architecture profile. It can be enabled otherwise by specifying @samp{--fix-cortex-a8}, or disabled unconditionally by specifying @samp{--no-fix-cortex-a8}.
+
+The erratum only affects Thumb-2 code. Please contact ARM for further details.
+
+@cindex Cortex-A53 erratum 835769 workaround
+@kindex --fix-cortex-a53-835769
+@kindex --no-fix-cortex-a53-835769
+The @samp{--fix-cortex-a53-835769} switch enables a link-time workaround for erratum 835769 present on certain early revisions of Cortex-A53 processors. The workaround is disabled by default. It can be enabled by specifying @samp{--fix-cortex-a53-835769}, or disabled unconditionally by specifying @samp{--no-fix-cortex-a53-835769}.
+
+Please contact ARM for further details.
+
+@kindex --merge-exidx-entries
+@kindex --no-merge-exidx-entries
+@cindex Merging exidx entries
+The @samp{--no-merge-exidx-entries} switch disables the merging of adjacent exidx entries in debuginfo.
+
+@kindex --long-plt
+@cindex 32-bit PLT entries
+The @samp{--long-plt} option enables the use of 16 byte PLT entries
+which support up to 4Gb of code. The default is to use 12 byte PLT
+entries which only support 512Mb of code.
+
+@kindex --no-apply-dynamic-relocs
+@cindex AArch64 rela addend
+The @samp{--no-apply-dynamic-relocs} option makes AArch64 linker do not apply
+link-time values for dynamic relocations.
+
@ifclear GENERIC
@lowersections
@end ifclear
@end ifclear
@end ifset
+@ifset MIPS
+@ifclear GENERIC
+@raisesections
+@end ifclear
+
+@node MIPS
+@section @command{ld} and the MIPS family
+
+@cindex MIPS microMIPS instruction choice selection
+@kindex --insn32
+@kindex --no-insn32
+The @samp{--insn32} and @samp{--no-insn32} options control the choice of
+microMIPS instructions used in code generated by the linker, such as that
+in the PLT or lazy binding stubs, or in relaxation. If @samp{--insn32} is
+used, then the linker only uses 32-bit instruction encodings. By default
+or if @samp{--no-insn32} is used, all instruction encodings are used,
+including 16-bit ones where possible.
+
+@ifclear GENERIC
+@lowersections
+@end ifclear
+@end ifset
+
@ifset MMIX
@ifclear GENERIC
@raisesections
@end ifclear
@end ifset
+@ifset NDS32
+@ifclear GENERIC
+@raisesections
+@end ifclear
+
+@node NDS32
+@section @code{ld} and NDS32
+@kindex relaxing on NDS32
+For NDS32, there are some options to select relaxation behavior. The linker
+relaxes objects according to these options.
+
+@table @code
+@item @samp{--m[no-]fp-as-gp}
+Disable/enable fp-as-gp relaxation.
+
+@item @samp{--mexport-symbols=FILE}
+Exporting symbols and their address into FILE as linker script.
+
+@item @samp{--m[no-]ex9}
+Disable/enable link-time EX9 relaxation.
+
+@item @samp{--mexport-ex9=FILE}
+Export the EX9 table after linking.
+
+@item @samp{--mimport-ex9=FILE}
+Import the Ex9 table for EX9 relaxation.
+
+@item @samp{--mupdate-ex9}
+Update the existing EX9 table.
+
+@item @samp{--mex9-limit=NUM}
+Maximum number of entries in the ex9 table.
+
+@item @samp{--mex9-loop-aware}
+Avoid generating the EX9 instruction inside the loop.
+
+@item @samp{--m[no-]ifc}
+Disable/enable the link-time IFC optimization.
+
+@item @samp{--mifc-loop-aware}
+Avoid generating the IFC instruction inside the loop.
+@end table
+
+@ifclear GENERIC
+@lowersections
+@end ifclear
+@end ifset
+
+@ifset NIOSII
+@ifclear GENERIC
+@raisesections
+@end ifclear
+
+@node Nios II
+@section @command{ld} and the Altera Nios II
+@cindex Nios II call relaxation
+@kindex --relax on Nios II
+
+Call and immediate jump instructions on Nios II processors are limited to
+transferring control to addresses in the same 256MB memory segment,
+which may result in @command{ld} giving
+@samp{relocation truncated to fit} errors with very large programs.
+The command-line option @option{--relax} enables the generation of
+trampolines that can access the entire 32-bit address space for calls
+outside the normal @code{call} and @code{jmpi} address range. These
+trampolines are inserted at section boundaries, so may not themselves
+be reachable if an input section and its associated call trampolines are
+larger than 256MB.
+
+The @option{--relax} option is enabled by default unless @option{-r}
+is also specified. You can disable trampoline generation by using the
+@option{--no-relax} linker option. You can also disable this optimization
+locally by using the @samp{set .noat} directive in assembly-language
+source files, as the linker-inserted trampolines use the @code{at}
+register as a temporary.
+
+Note that the linker @option{--relax} option is independent of assembler
+relaxation options, and that using the GNU assembler's @option{-relax-all}
+option interferes with the linker's more selective call instruction relaxation.
+
+@ifclear GENERIC
+@lowersections
+@end ifclear
+@end ifset
+
@ifset POWERPC
@ifclear GENERIC
@raisesections
@cindex PowerPC64 dot symbols
@kindex --dotsyms
@kindex --no-dotsyms
-@item --dotsyms, --no-dotsyms
+@item --dotsyms
+@itemx --no-dotsyms
These two options control how @command{ld} interprets version patterns
in a version script. Older PowerPC64 compilers emitted both a
function descriptor symbol with the same name as the function, and a
dot-prefixed patterns. Use @samp{--no-dotsyms} to disable this
feature.
+@cindex PowerPC64 register save/restore functions
+@kindex --save-restore-funcs
+@kindex --no-save-restore-funcs
+@item --save-restore-funcs
+@itemx --no-save-restore-funcs
+These two options control whether PowerPC64 @command{ld} automatically
+provides out-of-line register save and restore functions used by
+@samp{-Os} code. The default is to provide any such referenced
+function for a normal final link, and to not do so for a relocatable
+link.
+
@cindex PowerPC64 TLS optimization
@kindex --no-tls-optimize
@item --no-tls-optimize
sequences used to access Thread-Local Storage. Use this option to
disable the optimization.
+@cindex PowerPC64 __tls_get_addr optimization
+@kindex --tls-get-addr-optimize
+@kindex --no-tls-get-addr-optimize
+@item --tls-get-addr-optimize
+@itemx --no-tls-get-addr-optimize
+These options control whether PowerPC64 @command{ld} uses a special
+stub to call __tls_get_addr. PowerPC64 glibc 2.22 and later support
+an optimization that allows the second and subsequent calls to
+@code{__tls_get_addr} for a given symbol to be resolved by the special
+stub without calling in to glibc. By default the linker enables this
+option when glibc advertises the availability of __tls_get_addr_opt.
+Forcing this option on when using an older glibc won't do much besides
+slow down your applications, but may be useful if linking an
+application against an older glibc with the expectation that it will
+normally be used on systems having a newer glibc.
+
@cindex PowerPC64 OPD optimization
@kindex --no-opd-optimize
@item --no-opd-optimize
@item --plt-align
@itemx --no-plt-align
Use these options to control whether individual PLT call stubs are
-aligned to a 32-byte boundary, or to the specified power of two
-boundary when using @code{--plt-align=}. By default PLT call stubs
-are packed tightly.
+padded so that they don't cross a 32-byte boundary, or to the
+specified power of two boundary when using @code{--plt-align=}. Note
+that this isn't alignment in the usual sense. By default PLT call
+stubs are packed tightly.
@cindex PowerPC64 PLT call stub static chain
@kindex --plt-static-chain
tools will be able to process object files employing this GNU extension,
but will fail to respect the alignment instructions, and may issue noisy
warnings about unknown linker directives.
+
@end table
@ifclear GENERIC
projects / deliverable / binutils-gdb.git / blobdiff