\input texinfo
@setfilename ld.info
-@c Copyright (C) 1991-2014 Free Software Foundation, Inc.
+@c Copyright (C) 1991-2015 Free Software Foundation, Inc.
@syncodeindex ky cp
@c man begin INCLUDE
@include configdoc.texi
@end ifset
version @value{VERSION}.
-Copyright @copyright{} 1991-2014 Free Software Foundation, Inc.
+Copyright @copyright{} 1991-2015 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{} 1991-2014 Free Software Foundation, Inc.
+Copyright @copyright{} 1991-2015 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
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
Disables multiple reloc sections combining.
@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 visibile to the resulting shared library. Supported for
+i386 and x86-64.
+
@end table
Other keywords are ignored for Solaris compatibility.
needed or not. @option{--as-needed} causes a DT_NEEDED tag to only be
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 libraries, a
-non-weak undefined symbol reference from another dynamic library.
+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
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
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.
+
@kindex --reduce-memory-overheads
@item --reduce-memory-overheads
This option reduces memory requirements at ld runtime, at the expense of
@item --build-id
@itemx --build-id=@var{style}
Request the creation of a @code{.note.gnu.build-id} ELF note section
-or a @code{.build-id} COFF section. The contents of the note are
+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,
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
@kindex --insert-timestamp
@item --insert-timestamp
-Insert a real timestamp into the image, rather than the default value
-of zero. This will result in a slightly different results with each
-invocation, which could be helpful for distributing unique images.
+@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 tiem 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 indentical sources will compare
+identically.
@end table
@c man end
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
@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
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
@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
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
@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
but will fail to respect the alignment instructions, and may issue noisy
warnings about unknown linker directives.
-@cindex default manifest
-@item default manifest
-The linker will automatically add a default manifest to the .rsrc
-section of any fully linked cygwin or MingGW binary. This manifest is
-necessary in order to be able to execute the binary under Windows 8
-(or later). An application can supply its own manifest, and if it
-does so then this manifest will be used in preference to the default
-one.
@end table
@ifclear GENERIC
projects / deliverable / binutils-gdb.git / blobdiff