\input texinfo
@setfilename ld.info
-@c Copyright (C) 1991-2019 Free Software Foundation, Inc.
+@c Copyright (C) 1991-2021 Free Software Foundation, Inc.
@syncodeindex ky cp
@c man begin INCLUDE
@include configdoc.texi
@set MSP430
@set NDS32
@set NIOSII
+@set PDP11
@set POWERPC
@set POWERPC64
@set Renesas
@end ifset
version @value{VERSION}.
-Copyright @copyright{} 1991-2019 Free Software Foundation, Inc.
+Copyright @copyright{} 1991-2021 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{} 1991-2019 Free Software Foundation, Inc.
+Copyright @copyright{} 1991-2021 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
* Overview:: Overview
* Invocation:: Invocation
* Scripts:: Linker Scripts
+* Plugins:: Linker Plugins
@ifset GENERIC
* Machine Dependent:: Machine Dependent Features
@end ifset
option is only meaningful on ELF platforms supporting the rtld-audit interface.
The -P option is provided for Solaris compatibility.
+@kindex --enable-non-contiguous-regions
+@item --enable-non-contiguous-regions
+This option avoids generating an error if an input section does not
+fit a matching output section. The linker tries to allocate the input
+section to subseque nt matching output sections, and generates an
+error only if no output section is large enough. This is useful when
+several non-contiguous memory regions are available and the input
+section does not require a particular one. The order in which input
+sections are evaluated does not change, for instance:
+
+@smallexample
+ MEMORY @{
+ MEM1 (rwx) : ORIGIN : 0x1000, LENGTH = 0x14
+ MEM2 (rwx) : ORIGIN : 0x1000, LENGTH = 0x40
+ MEM3 (rwx) : ORIGIN : 0x2000, LENGTH = 0x40
+ @}
+ SECTIONS @{
+ mem1 : @{ *(.data.*); @} > MEM1
+ mem2 : @{ *(.data.*); @} > MEM2
+ mem3 : @{ *(.data.*); @} > MEM2
+ @}
+
+ with input sections:
+ .data.1: size 8
+ .data.2: size 0x10
+ .data.3: size 4
+
+ results in .data.1 affected to mem1, and .data.2 and .data.3
+ affected to mem2, even though .data.3 would fit in mem3.
+@end smallexample
+
+This option is incompatible with INSERT statements because it changes
+the way input sections are mapped to output sections.
+
+@kindex --enable-non-contiguous-regions-warnings
+@item --enable-non-contiguous-regions-warnings
+This option enables warnings when
+@code{--enable-non-contiguous-regions} allows possibly unexpected
+matches in sections mapping, potentially leading to silently
+discarding a section instead of failing because it does not fit any
+output region.
+
@cindex entry point, from command line
@kindex -e @var{entry}
@kindex --entry=@var{entry}
support a similar function to export all symbols from a DLL or EXE; see
the description of @samp{--export-all-symbols} below.
+@kindex --export-dynamic-symbol=@var{glob}
+@cindex export dynamic symbol
+@item --export-dynamic-symbol=@var{glob}
+When creating a dynamically linked executable, symbols matching
+@var{glob} will be added to the dynamic symbol table. When creating a
+shared library, references to symbols matching @var{glob} will not be
+bound to the definitions within the shared library. This option is a
+no-op when creating a shared library and @samp{-Bsymbolic} or
+@samp{--dynamic-list} are not specified. This option is only meaningful
+on ELF platforms which support shared libraries.
+
+@kindex --export-dynamic-symbol-list=@var{file}
+@cindex export dynamic symbol list
+@item --export-dynamic-symbol-list=@var{file}
+Specify a @samp{--export-dynamic-symbol} for each pattern in the file.
+The format of the file is the same as the version node without
+scope and node name. See @ref{VERSION} for more information.
+
@ifclear SingleFormat
@cindex big-endian objects
@cindex endianness
in the filter object. The shared object @var{name} need not exist.
Thus the shared object @var{name} may be used to provide an alternative
implementation of certain functions, perhaps for debugging or for
-machine specific performance.
+machine-specific performance.
This option may be specified more than once. The DT_AUXILIARY entries
will be created in the order in which they appear on the command line.
See @ref{Expressions} for more information about expressions in linker
scripts.
-@item How GNU properties are merged.
+@item
+How GNU properties are merged.
-When linker merges input .note.gnu.property sections into one output
-.note.gnu.property section, some properties are removed or updated,
-which are reported in the link map as
+When the linker merges input .note.gnu.property sections into one output
+.note.gnu.property section, some properties are removed or updated.
+These actions are reported in the link map. For example:
@smallexample
Removed property 0xc0000002 to merge foo.o (0x1) and bar.o (not found)
@end smallexample
-It indicates that property 0xc0000002 is removed from output when
+This indicates that property 0xc0000002 is removed from output when
merging properties in @file{foo.o}, whose property 0xc0000002 value
is 0x1, and @file{bar.o}, which doesn't have property 0xc0000002.
@smallexample
-Updated property 0xc0000002 (0x1) to merge foo.o (0x1) and bar.o (0x1)
+Updated property 0xc0010001 (0x1) to merge foo.o (0x1) and bar.o (0x1)
@end smallexample
-It indicates that property 0xc0010001 value is updated to 0x1 in output
+This indicates that property 0xc0010001 value is updated to 0x1 in output
when merging properties in @file{foo.o}, whose 0xc0010001 property value
is 0x1, and @file{bar.o}, whose 0xc0010001 property value is 0x1.
@end itemize
+@cindex link map discarded
+@kindex --print-map-discarded
+@kindex --no-print-map-discarded
+@item --print-map-discarded
+@itemx --no-print-map-discarded
+Print (or do not print) the list of discarded and garbage collected sections
+in the link map. Enabled by default.
+
@kindex -n
@cindex read-only text
@cindex NMAGIC
option is not specified, the name @file{a.out} is used by default. The
script command @code{OUTPUT} can also specify the output file name.
+@kindex --dependency-file=@var{depfile}
+@cindex dependency file
+@item --dependency-file=@var{depfile}
+Write a @dfn{dependency file} to @var{depfile}. This file contains a rule
+suitable for @code{make} describing the output file and all the input files
+that were read to produce it. The output is similar to the compiler's
+output with @samp{-M -MP} (@pxref{Preprocessor Options,, Options
+Controlling the Preprocessor, gcc.info, Using the GNU Compiler
+Collection}). Note that there is no option like the compiler's @samp{-MM},
+to exclude ``system files'' (which is not a well-specified concept in the
+linker, unlike ``system headers'' in the compiler). So the output from
+@samp{--dependency-file} is always specific to the exact state of the
+installation where it was produced, and should not be copied into
+distributed makefiles without careful editing.
+
@kindex -O @var{level}
@cindex generating optimized output
@item -O @var{level}
from the place where the @command{ar}, @command{nm} and
@command{ranlib} programs search for their plugins. In order for
those commands to make use of a compiler based plugin it must first be
-copied into the @file{$@{bindir@}/../lib/bfd-plugins} directory. All gcc
+copied into the @file{$@{libdir@}/bfd-plugins} directory. All gcc
based linker plugins are backward compatible, so it is sufficient to
just copy in the newest one.
so that symbols in this shared library interpose all other shared
libraries not so marked.
+@item unique
+@itemx nounique
+When generating a shared library or other dynamically loadable ELF
+object mark it as one that should (by default) only ever be loaded once,
+and only in the main namespace (when using @code{dlmopen}). This is
+primarily used to mark fundamental libraries such as libc, libpthread et
+al which do not usually function correctly unless they are the sole instances
+of themselves. This behaviour can be overridden by the @code{dlmopen} caller
+and does not apply to certain loading mechanisms (such as audit libraries).
+
+@item lam-u48
+Generate GNU_PROPERTY_X86_FEATURE_1_LAM_U48 in .note.gnu.property section
+to indicate compatibility with Intel LAM_U48. Supported for Linux/x86_64.
+
+@item lam-u57
+Generate GNU_PROPERTY_X86_FEATURE_1_LAM_U57 in .note.gnu.property section
+to indicate compatibility with Intel LAM_U57. Supported for Linux/x86_64.
+
+@item lam-u48-report=none
+@itemx lam-u48-report=warning
+@itemx lam-u48-report=error
+Specify how to report the missing GNU_PROPERTY_X86_FEATURE_1_LAM_U48
+property in input .note.gnu.property section.
+@option{lam-u48-report=none}, which is the default, will make the
+linker not report missing properties in input files.
+@option{lam-u48-report=warning} will make the linker issue a warning for
+missing properties in input files. @option{lam-u48-report=error} will
+make the linker issue an error for missing properties in input files.
+Supported for Linux/x86_64.
+
+@item lam-u57-report=none
+@itemx lam-u57-report=warning
+@itemx lam-u57-report=error
+Specify how to report the missing GNU_PROPERTY_X86_FEATURE_1_LAM_U57
+property in input .note.gnu.property section.
+@option{lam-u57-report=none}, which is the default, will make the
+linker not report missing properties in input files.
+@option{lam-u57-report=warning} will make the linker issue a warning for
+missing properties in input files. @option{lam-u57-report=error} will
+make the linker issue an error for missing properties in input files.
+Supported for Linux/x86_64.
+
+@item lam-report=none
+@itemx lam-report=warning
+@itemx lam-report=error
+Specify how to report the missing GNU_PROPERTY_X86_FEATURE_1_LAM_U48 and
+GNU_PROPERTY_X86_FEATURE_1_LAM_U57 properties in input .note.gnu.property
+section. @option{lam-report=none}, which is the default, will make the
+linker not report missing properties in input files.
+@option{lam-report=warning} will make the linker issue a warning for
+missing properties in input files. @option{lam-report=error} will make
+the linker issue an error for missing properties in input files.
+Supported for Linux/x86_64.
+
@item lazy
When generating an executable or shared library, mark it to tell the
dynamic linker to defer function call resolution to the point when
be in wholly disjoint pages from any other data. Don't create separate
code @code{PT_LOAD} segment if @samp{noseparate-code} is used.
+@item unique-symbol
+@itemx nounique-symbol
+Avoid duplicated local symbol names in the symbol string table. Append
+".@code{number}" to duplicated local symbol names if @samp{unique-symbol}
+is used. @option{nounique-symbol} is the default.
+
@item shstk
Generate GNU_PROPERTY_X86_FEATURE_1_SHSTK in .note.gnu.property section
to indicate compatibility with Intel Shadow Stack. Supported for
Specifying zero will override any default non-zero sized
@code{PT_GNU_STACK} segment creation.
+@item start-stop-visibility=@var{value}
+@cindex visibility
+@cindex ELF symbol visibility
+Specify the ELF symbol visibility for synthesized
+@code{__start_SECNAME} and @code{__stop_SECNAME} symbols (@pxref{Input
+Section Example}). @var{value} must be exactly @samp{default},
+@samp{internal}, @samp{hidden}, or @samp{protected}. If no @samp{-z
+start-stop-visibility} option is given, @samp{protected} is used for
+compatibility with historical practice. However, it's highly
+recommended to use @samp{-z start-stop-visibility=hidden} in new
+programs and shared libraries so that these symbols are not exported
+between shared objects, which is not usually what's intended.
+
@item text
@itemx notext
@itemx textoff
-Report an error if DT_TEXTREL is set, i.e., if the binary has dynamic
-relocations in read-only sections. Don't report an error if
-@samp{notext} or @samp{textoff}.
+Report an error if DT_TEXTREL is set, i.e., if the position-independent
+or shared object has dynamic relocations in read-only sections. Don't
+report an error if @samp{notext} or @samp{textoff}.
@item undefs
Do not report unresolved symbol references from regular object files,
either when creating an executable, or when creating a shared library.
This option is the inverse of @samp{-z defs}.
+@item x86-64-baseline
+@item x86-64-v2
+@item x86-64-v3
+@itemx x86-64-v4
+Specify the x86-64 ISA level needed in .note.gnu.property section.
+@option{x86-64-baseline} generates @code{GNU_PROPERTY_X86_ISA_1_BASELINE}.
+@option{x86-64-v2} generates @code{GNU_PROPERTY_X86_ISA_1_V2}.
+@option{x86-64-v3} generates @code{GNU_PROPERTY_X86_ISA_1_V3}.
+@option{x86-64-v4} generates @code{GNU_PROPERTY_X86_ISA_1_V4}.
+Supported for Linux/i386 and Linux/x86_64.
+
@end table
Other keywords are ignored for Solaris compatibility.
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 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.
+within the shared library. This option is only meaningful on ELF
+platforms which support shared libraries.
@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 and position independent executables.
+libraries.
@kindex --dynamic-list=@var{dynamic-list-file}
@item --dynamic-list=@var{dynamic-list-file}
where this happens appear next. Finally any files that reference the
symbol are listed.
+@cindex ctf variables
+@kindex --ctf-variables
+@kindex --no-ctf-variables
+@item --ctf-variables
+@item --no-ctf-variables
+The CTF debuginfo format supports a section which encodes the names and
+types of variables found in the program which do not appear in any symbol
+table. These variables clearly cannot be looked up by address by
+conventional debuggers, so the space used for their types and names is
+usually wasted: the types are usually small but the names are often not.
+@option{--ctf-variables} causes the generation of such a section.
+The default behaviour can be restored with @option{--no-ctf-variables}.
+
+@cindex ctf type sharing
+@kindex --ctf-share-types
+@item --ctf-share-types=@var{method}
+Adjust the method used to share types between translation units in CTF.
+
+@table @samp
+@item share-unconflicted
+Put all types that do not have ambiguous definitions into the shared dictionary,
+where debuggers can easily access them, even if they only occur in one
+translation unit. This is the default.
+
+@item share-duplicated
+Put only types that occur in multiple translation units into the shared
+dictionary: types with only one definition go into per-translation-unit
+dictionaries. Types with ambiguous definitions in multiple translation units
+always go into per-translation-unit dictionaries. This tends to make the CTF
+larger, but may reduce the amount of CTF in the shared dictionary. For very
+large projects this may speed up opening the CTF and save memory in the CTF
+consumer at runtime.
+@end table
+
@cindex common allocation
@kindex --no-define-common
@item --no-define-common
@emph{Note:} there should be no white space between @var{symbol}, the
equals sign (``@key{=}''), and @var{expression}.
+The linker processes @samp{--defsym} arguments and @samp{-T} arguments
+in order, placing @samp{--defsym} before @samp{-T} will define the
+symbol before the linker script from @samp{-T} is processed, while
+placing @samp{--defsym} after @samp{-T} will define the symbol after
+the linker script has been processed. This difference has
+consequences for expressions within the linker script that use the
+@samp{--defsym} symbols, which order is correct will depend on what
+you are trying to achieve.
+
@cindex demangling, from command line
@kindex --demangle[=@var{style}]
@kindex --no-demangle
@kindex --embedded-relocs
@item --embedded-relocs
This option is similar to the @option{--emit-relocs} option except
-that the relocs are stored in a target specific section. This option
+that the relocs are stored in a target-specific section. This option
is only supported by the @samp{BFIN}, @samp{CR16} and @emph{M68K}
targets.
@samp{--undefined}, or @samp{--gc-keep-exported} or by a @code{ENTRY}
command in the linker script.
+As a GNU extension, ELF input sections marked with the
+@code{SHF_GNU_RETAIN} flag will not be garbage collected.
+
@kindex --print-gc-sections
@kindex --no-print-gc-sections
@cindex garbage collection
@kindex --target-help
@item --target-help
-Print a summary of all target specific options on the standard output and exit.
+Print a summary of all target-specific options on the standard output and exit.
@kindex -Map=@var{mapfile}
@item -Map=@var{mapfile}
Print a link map to the file @var{mapfile}. See the description of the
-@option{-M} option, above.
+@option{-M} option, above. If @var{mapfile} is just the character
+@code{-} then the map will be written to stdout.
+
+Specifying a directory as @var{mapfile} causes the linker map to be
+written as a file inside the directory. Normally name of the file
+inside the directory is computed as the basename of the @var{output}
+file with @code{.map} appended. If however the special character
+@code{%} is used then this will be replaced by the full path of the
+output file. Additionally if there are any characters after the
+@var{%} symbol then @code{.map} will no longer be appended.
+
+@smallexample
+ -o foo.exe -Map=bar [Creates ./bar]
+ -o ../dir/foo.exe -Map=bar [Creates ./bar]
+ -o foo.exe -Map=../dir [Creates ../dir/foo.exe.map]
+ -o ../dir2/foo.exe -Map=../dir [Creates ../dir/foo.exe.map]
+ -o foo.exe -Map=% [Creates ./foo.exe.map]
+ -o ../dir/foo.exe -Map=% [Creates ../dir/foo.exe.map]
+ -o foo.exe -Map=%.bar [Creates ./foo.exe.bar]
+ -o ../dir/foo.exe -Map=%.bar [Creates ../dir/foo.exe.bar]
+ -o ../dir2/foo.exe -Map=../dir/% [Creates ../dir/../dir2/foo.exe.map]
+ -o ../dir2/foo.exe -Map=../dir/%.bar [Creates ../dir/../dir2/foo.exe.bar]
+@end smallexample
+
+It is an error to specify more than one @code{%} character.
+
+If the map file already exists then it will be overwritten by this
+operation.
@cindex memory usage
@kindex --no-keep-memory
appropriate memset function.
@end itemize
+@kindex --error-handling-script=@var{scriptname}
+@item --error-handling-script=@var{scriptname}
+If this option is provided then the linker will invoke
+@var{scriptname} whenever an error is encountered. Currently however
+only two kinds of error are supported: missing symbols and missing
+libraries. Two arguments will be passed to script: the keyword
+``undefined-symbol'' or `missing-lib'' and the @var{name} of the
+undefined symbol or missing library. The intention is that the script
+will provide suggestions to the user as to where the symbol or library
+might be found. After the script has finished then the normal linker
+error message will be displayed.
+
+The availability of this option is controlled by a configure time
+switch, so it may not be present in specific implementations.
+
@kindex --no-undefined-version
@item --no-undefined-version
Normally when a symbol has an undefined version, the linker will ignore
@xref{PowerPC ELF32,,@command{ld} and PowerPC 32-bit ELF Support}.
@end ifset
-On some platforms the @samp{--relax} option performs target specific,
+On some platforms the @option{--relax} option performs target specific,
global optimizations that become possible when the linker resolves
addressing in the program, such as relaxing address modes,
synthesizing new instructions, selecting shorter version of current
family of processors.
@end ifset
-@ifset GENERIC
-On platforms where this is not supported, @samp{--relax} is accepted,
-but ignored.
-@end ifset
-
-On platforms where @samp{--relax} is accepted the option
-@samp{--no-relax} can be used to disable the feature.
+On platforms where the feature is supported, the option
+@option{--no-relax} will disable it.
+On platforms where the feature is not supported, both @option{--relax}
+and @option{--no-relax} are accepted, but ignored.
+
@cindex retaining specified symbols
@cindex stripping all but some symbols
@cindex symbols, retaining selectively
Add a directory to the runtime library search path. This is used when
linking an ELF executable with shared objects. All @option{-rpath}
arguments are concatenated and passed to the runtime linker, which uses
-them to locate shared objects at runtime. The @option{-rpath} option is
-also used when locating shared objects which are needed by shared
-objects explicitly included in the link; see the description of the
-@option{-rpath-link} option. If @option{-rpath} is not used when linking an
-ELF executable, the contents of the environment variable
-@code{LD_RUN_PATH} will be used if it is defined.
+them to locate shared objects at runtime.
+
+The @option{-rpath} option is also used when locating shared objects which
+are needed by shared objects explicitly included in the link; see the
+description of the @option{-rpath-link} option. Searching @option{-rpath}
+in this way is only supported by native linkers and cross linkers which
+have been configured with the @option{--with-sysroot} option.
+
+If @option{-rpath} is not used when linking an ELF executable, the
+contents of the environment variable @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 path out of all the
The linker uses the following search paths to locate required shared
libraries:
+
@enumerate
@item
Any directories specified by @option{-rpath-link} options.
@item
The default directories, normally @file{/lib} and @file{/usr/lib}.
@item
-For a native linker on an ELF system, if the file @file{/etc/ld.so.conf}
-exists, the list of directories found in that file.
+For a linker for a Linux system, if the file @file{/etc/ld.so.conf}
+exists, the list of directories found in that file. Note: the path
+to this file is prefixed with the @code{sysroot} value, if that is
+defined, and then any @code{prefix} string if the linker was
+configured with the @command{--prefix=<path>} option.
+@item
+For a native linker on a FreeBSD system, any directories specified by
+the @code{_PATH_ELF_HINTS} macro defined in the @file{elf-hints.h}
+header file.
+@item
+Any directories specifed by a @code{SEARCH_DIR} command in the
+linker script being used.
@end enumerate
If the required shared library is not found, the linker will issue a
is, if the @code{SECTIONS} command does not specify a start address for
the section (@pxref{SECTIONS}).
-@kindex --warn-shared-textrel
-@item --warn-shared-textrel
-Warn if the linker adds a DT_TEXTREL to a shared object.
+@kindex --warn-textrel
+@item --warn-textrel
+Warn if the linker adds DT_TEXTREL to a position-independent executable
+or shared object.
@kindex --warn-alternate-em
@item --warn-alternate-em
@}
@end smallexample
-Please keep in mind that with link-time optimization (LTO) enabled, your whole
-program may be a translation unit.
-
@kindex --eh-frame-hdr
@kindex --no-eh-frame-hdr
@item --eh-frame-hdr
@kindex --high-entropy-va
@item --high-entropy-va
+@itemx --disable-high-entropy-va
Image is compatible with 64-bit address space layout randomization
-(ASLR).
+(ASLR). This option is enabled by default for 64-bit PE images.
+
+This option also implies @option{--dynamicbase} and
+@option{--enable-reloc-section}.
@kindex --dynamicbase
@item --dynamicbase
+@itemx --disable-dynamicbase
The image base address may be relocated using address space layout
randomization (ASLR). This feature was introduced with MS Windows
-Vista for i386 PE targets.
+Vista for i386 PE targets. This option is enabled by default but
+can be disabled via the @option{--disable-dynamicbase} option.
+This option also implies @option{--enable-reloc-section}.
@kindex --forceinteg
@item --forceinteg
-Code integrity checks are enforced.
+@itemx --disable-forceinteg
+Code integrity checks are enforced. This option is disabled by
+default.
@kindex --nxcompat
@item --nxcompat
+@item --disable-nxcompat
The image is compatible with the Data Execution Prevention.
-This feature was introduced with MS Windows XP SP2 for i386 PE targets.
+This feature was introduced with MS Windows XP SP2 for i386 PE
+targets. The option is enabled by default.
@kindex --no-isolation
@item --no-isolation
+@itemx --disable-no-isolation
Although the image understands isolation, do not isolate the image.
+This option is disabled by default.
@kindex --no-seh
@item --no-seh
+@itemx --disable-no-seh
The image does not use SEH. No SE handler may be called from
-this image.
+this image. This option is disabled by default.
@kindex --no-bind
@item --no-bind
-Do not bind this image.
+@itemx --disable-no-bind
+Do not bind this image. This option is disabled by default.
@kindex --wdmdriver
@item --wdmdriver
-The driver uses the MS Windows Driver Model.
+@itemx --disable-wdmdriver
+The driver uses the MS Windows Driver Model. This option is disabled
+by default.
@kindex --tsaware
@item --tsaware
-The image is Terminal Server aware.
+@itemx --disable-tsaware
+The image is Terminal Server aware. This option is disabled by
+default.
@kindex --insert-timestamp
@item --insert-timestamp
can be used to insert a zero value for the timestamp, this ensuring
that binaries produced from identical sources will compare
identically.
+
+@kindex --enable-reloc-section
+@item --enable-reloc-section
+@itemx --disable-reloc-section
+Create the base relocation table, which is necessary if the image
+is loaded at a different image base than specified in the PE header.
+This option is enabled by default.
@end table
@c man end
a check is made causing the loss of an ISA mode transition to produce
an error.
+@kindex --compact-branches
+@item --compact-branches
+@kindex --no-compact-branches
+@itemx --no-compact-branches
+These options control the generation of compact instructions by the linker
+in the PLT entries for MIPS R6.
+
+@end table
+
+@c man end
+@end ifset
+
+
+@ifset PDP11
+@subsection Options specific to PDP11 targets
+
+@c man begin OPTIONS
+
+For the pdp11-aout target, three variants of the output format can be
+produced as selected by the following options. The default variant
+for pdp11-aout is the @samp{--omagic} option, whereas for other
+targets @samp{--nmagic} is the default. The @samp{--imagic} option is
+defined only for the pdp11-aout target, while the others are described
+here as they apply to the pdp11-aout target.
+
+@table @gcctabopt
+
+@kindex -N
+@item -N
+@kindex --omagic
+@itemx --omagic
+
+Mark the output as @code{OMAGIC} (0407) in the @file{a.out} header to
+indicate that the text segment is not to be write-protected and
+shared. Since the text and data sections are both readable and
+writable, the data section is allocated immediately contiguous after
+the text segment. This is the oldest format for PDP11 executable
+programs and is the default for @command{ld} on PDP11 Unix systems
+from the beginning through 2.11BSD.
+
+@kindex -n
+@item -n
+@kindex --nmagic
+@itemx --nmagic
+
+Mark the output as @code{NMAGIC} (0410) in the @file{a.out} header to
+indicate that when the output file is executed, the text portion will
+be read-only and shareable among all processes executing the same
+file. This involves moving the data areas up to the first possible 8K
+byte page boundary following the end of the text. This option creates
+a @emph{pure executable} format.
+
+@kindex -z
+@item -z
+@kindex --imagic
+@itemx --imagic
+
+Mark the output as @code{IMAGIC} (0411) in the @file{a.out} header to
+indicate that when the output file is executed, the program text and
+data areas will be loaded into separate address spaces using the split
+instruction and data space feature of the memory management unit in
+larger models of the PDP11. This doubles the address space available
+to the program. The text segment is again pure, write-protected, and
+shareable. The only difference in the output format between this
+option and the others, besides the magic number, is that both the text
+and data sections start at location 0. The @samp{-z} option selected
+this format in 2.11BSD. This option creates a @emph{separate
+executable} format.
+
+@kindex --no-omagic
+@item --no-omagic
+
+Equivalent to @samp{--nmagic} for pdp11-aout.
+
@end table
@c man end
@item
the @code{ENTRY(@var{symbol})} command in a linker script;
@item
-the value of a target specific symbol, if it is defined; For many
+the value of a target-specific symbol, if it is defined; For many
targets this is @code{start}, but PE- and BeOS-based systems for example
check a list of possible entry symbols, matching the first one found.
@item
In case a @dfn{sysroot prefix} is configured, and the filename starts
with the @samp{/} character, and the script being processed was
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.
-The @dfn{sysroot prefix} can also be forced by specifying @code{=}
-as the first character in the filename path, or prefixing the filename
-path with @code{$SYSROOT}. See also the description of @samp{-L} in
-@ref{Options,,Command-line Options}.
+for in the @dfn{sysroot prefix}. The @dfn{sysroot prefix} can also be forced by specifying
+@code{=} as the first character in the filename path, or prefixing the
+filename path with @code{$SYSROOT}. See also the description of
+@samp{-L} in @ref{Options,,Command-line Options}.
+
+If a @dfn{sysroot prefix} is not used then the linker will try to open
+the file in the directory containing the linker script. If it is not
+found the linker will then search the current directory. If it is still
+not found the linker will search through the archive library search
+path.
If you use @samp{INPUT (-l@var{file})}, @command{ld} will transform the
name to @code{lib@var{file}.a}, as with the command-line argument
into ascending order by name before placing them in the output file.
@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
-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.
+@code{SORT_BY_ALIGNMENT} is similar to @code{SORT_BY_NAME}.
+@code{SORT_BY_ALIGNMENT} will sort sections into descending order of
+alignment before placing them in the output file. Placing larger
+alignments before smaller alignments can reduce the amount of padding
+needed.
@cindex SORT_BY_INIT_PRIORITY
-@code{SORT_BY_INIT_PRIORITY} is very similar to @code{SORT_BY_NAME}. The
-difference is @code{SORT_BY_INIT_PRIORITY} will sort sections into
-ascending order by numerical value of the GCC init_priority attribute
-encoded in the section name before placing them in the output file.
+@code{SORT_BY_INIT_PRIORITY} is also similar to @code{SORT_BY_NAME}.
+@code{SORT_BY_INIT_PRIORITY} will sort sections into ascending
+numerical order of the GCC init_priority attribute encoded in the
+section name before placing them in the output file. In
+@code{.init_array.NNNNN} and @code{.fini_array.NNNNN}, @code{NNNNN} is
+the init_priority. In @code{.ctors.NNNNN} and @code{.dtors.NNNNN},
+@code{NNNNN} is 65535 minus the init_priority.
@cindex SORT
@code{SORT} is an alias for @code{SORT_BY_NAME}.
input sections. Any input sections which are assigned to an output
section named @samp{/DISCARD/} are not included in the output file.
+This can be used to discard input sections marked with the ELF flag
+@code{SHF_GNU_RETAIN}, which would otherwise have been saved from linker
+garbage collection.
+
+Note, sections that match the @samp{/DISCARD/} output section will be
+discarded even if they are in an ELF section group which has other
+members which are not being discarded. This is deliberate.
+Discarding takes precedence over grouping.
+
@node Output Section Attributes
@subsection Output Section Attributes
@cindex output section attributes
@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}]
@{
@subsection Symbolic Constants
@cindex symbolic constants
@kindex CONSTANT
-It is possible to refer to target specific constants via the use of
+It is possible to refer to target-specific constants via the use of
the @code{CONSTANT(@var{name})} operator, where @var{name} is one of:
@table @code
at the position in the command line where the implicit linker script was
read. This can affect archive searching.
+@node Plugins
+@chapter Linker Plugins
+
+@cindex plugins
+@cindex linker plugins
+The linker can use dynamically loaded plugins to modify its behavior.
+For example, the link-time optimization feature that some compilers
+support is implemented with a linker plugin.
+
+Currently there is only one plugin shipped by default, but more may
+be added here later.
+
+@menu
+* libdep Plugin:: Static Library Dependencies Plugin
+@end menu
+
+@node libdep Plugin
+@section Static Library Dependencies Plugin
+@cindex static library dependencies
+Originally, static libraries were contained in an archive file consisting
+just of a collection of relocatable object files. Later they evolved to
+optionally include a symbol table, to assist in finding the needed objects
+within a library. There their evolution ended, and dynamic libraries
+rose to ascendance.
+
+One useful feature of dynamic libraries was that, more than just collecting
+multiple objects into a single file, they also included a list of their
+dependencies, such that one could specify just the name of a single dynamic
+library at link time, and all of its dependencies would be implicitly
+referenced as well. But static libraries lacked this feature, so if a
+link invocation was switched from using dynamic libraries to static
+libraries, the link command would usually fail unless it was rewritten to
+explicitly list the dependencies of the static library.
+
+The GNU @command{ar} utility now supports a @option{--record-libdeps} option
+to embed dependency lists into static libraries as well, and the @file{libdep}
+plugin may be used to read this dependency information at link time. The
+dependency information is stored as a single string, carrying @option{-l}
+and @option{-L} arguments as they would normally appear in a linker
+command line. As such, the information can be written with any text
+utility and stored into any archive, even if GNU @command{ar} is not
+being used to create the archive. The information is stored in an
+archive member named @samp{__.LIBDEP}.
+
+For example, given a library @file{libssl.a} that depends on another
+library @file{libcrypto.a} which may be found in @file{/usr/local/lib},
+the @samp{__.LIBDEP} member of @file{libssl.a} would contain
+
+@smallexample
+-L/usr/local/lib -lcrypto
+@end smallexample
+
@ifset GENERIC
@node Machine Dependent
@chapter Machine Dependent Features
@cindex PowerPC64 __tls_get_addr optimization
@kindex --tls-get-addr-optimize
@kindex --no-tls-get-addr-optimize
+@kindex --tls-get-addr-regsave
+@kindex --no-tls-get-addr-regsave
@item --tls-get-addr-optimize
@itemx --no-tls-get-addr-optimize
-These options control whether PowerPC64 @command{ld} uses a special
+These options control how 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.
+stub without calling in to glibc. By default the linker enables
+generation of the stub when glibc advertises the availability of
+__tls_get_addr_opt.
+Using @option{--tls-get-addr-optimize} with 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.
+@option{--tls-get-addr-regsave} forces generation of a stub that saves
+and restores volatile registers around the call into glibc. Normally,
+this is done when the linker detects a call to __tls_get_addr_desc.
+Such calls then go via the register saving stub to __tls_get_addr_opt.
+@option{--no-tls-get-addr-regsave} disables generation of the
+register saves.
@cindex PowerPC64 OPD optimization
@kindex --no-opd-optimize
code is used to insert TOC entries. Use this option to disable the
optimization.
+@cindex PowerPC64 inline PLT call optimization
+@kindex --no-inline-optimize
+@item --no-inline-optimize
+PowerPC64 @command{ld} normally replaces inline PLT call sequences
+marked with @code{R_PPC64_PLTSEQ}, @code{R_PPC64_PLTCALL},
+@code{R_PPC64_PLT16_HA} and @code{R_PPC64_PLT16_LO_DS} relocations by
+a number of @code{nop}s and a direct call when the function is defined
+locally and can't be overridden by some other definition. This option
+disables that optimization.
+
@cindex PowerPC64 multi-TOC
@kindex --no-multi-toc
@item --no-multi-toc
to become localentry:8. This will result in a dynamic loader
complaint and failure to run. The option is experimental, use with
care. @option{--no-plt-localentry} is the default.
+
+@cindex PowerPC64 Power10 stubs
+@kindex --power10-stubs
+@kindex --no-power10-stubs
+@item --power10-stubs
+@itemx --no-power10-stubs
+When PowerPC64 @command{ld} links input object files containing
+relocations used on power10 prefixed instructions it normally creates
+linkage stubs (PLT call and long branch) using power10 instructions
+for @code{@@notoc} PLT calls where @code{r2} is not known. The
+power10 notoc stubs are smaller and faster, so are preferred for
+power10. @option{--power10-stubs} and @option{--no-power10-stubs}
+allow you to override the linker's selection of stub instructions.
+@option{--power10-stubs=auto} allows the user to select the default
+auto mode.
@end table
@ifclear GENERIC
no-ops or widen density instructions to preserve branch target
alignment. There may still be some cases where no-ops are required to
preserve the correctness of the code.
+
+@item --abi-windowed
+@itemx --abi-call0
+Choose ABI for the output object and for the generated PLT code.
+PLT code inserted by the linker must match ABI of the output object
+because windowed and call0 ABI use incompatible function call
+conventions.
+Default ABI is chosen by the ABI tag in the @code{.xtensa.info} section
+of the first input object.
+A warning is issued if ABI tags of input objects do not match each other
+or the chosen output object ABI.
@end table
@ifclear GENERIC
projects / thirdparty / binutils-gdb.git / blobdiff