\input texinfo
@setfilename ld.info
-@c Copyright (C) 1991-2020 Free Software Foundation, Inc.
+@c Copyright (C) 1991-2021 Free Software Foundation, Inc.
@syncodeindex ky cp
@c man begin INCLUDE
@include configdoc.texi
@end ifset
version @value{VERSION}.
-Copyright @copyright{} 1991-2020 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{} 1991-2020 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
@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
+The @option{--push-state} allows one 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.
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
than the system page size will render this protection ineffective.
Don't create an ELF @code{PT_GNU_RELRO} segment if @samp{norelro}.
+@item report-relative-reloc
+Report dynamic relative relocations generated by linker. Supported for
+Linux/i386 and Linux/x86_64.
+
@item separate-code
@itemx noseparate-code
Create separate code @code{PT_LOAD} segment header in the object. This
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-gc
+@itemx nostart-stop-gc
+@cindex start-stop-gc
+When @samp{--gc-sections} is in effect, a reference from a retained
+section to @code{__start_SECNAME} or @code{__stop_SECNAME} causes all
+input sections named @code{SECNAME} to also be retained, if
+@code{SECNAME} is representable as a C identifier and either
+@code{__start_SECNAME} or @code{__stop_SECNAME} is synthesized by the
+linker. @samp{-z start-stop-gc} disables this effect, allowing
+sections to be garbage collected as if the special synthesized symbols
+were not defined. @samp{-z start-stop-gc} has no effect on a
+definition of @code{__start_SECNAME} or @code{__stop_SECNAME} in an
+object file or linker script. Such a definition will prevent the
+linker providing a synthesized @code{__start_SECNAME} or
+@code{__stop_SECNAME} respectively, and therefore the special
+treatment by garbage collection for those references.
+
@item start-stop-visibility=@var{value}
@cindex visibility
@cindex ELF symbol visibility
either when creating an executable, or when creating a shared library.
This option is the inverse of @samp{-z defs}.
+@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 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}.
needed. This is similar to the rules for extraction of object files
from archives. @option{--no-as-needed} restores the default behaviour.
+Note: On Linux based systems the @option{--as-needed} option also has
+an affect on the behaviour of the @option{--rpath} and
+@option{--rpath-link} options. See the description of
+@option{--rpath-link} for more details.
+
@kindex --add-needed
@kindex --no-add-needed
@item --add-needed
This option is only meaningful on ELF platforms which support shared
libraries.
+@kindex -Bno-symbolic
+@item -Bno-symbolic
+This option can cancel previously specified @samp{-Bsymbolic} and
+@samp{-Bsymbolic-functions}.
+
@kindex --dynamic-list=@var{dynamic-list-file}
@item --dynamic-list=@var{dynamic-list-file}
Specify the name of a dynamic list file to the linker. This is
@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
@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 -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. Specifying a directory as @var{mapfile}
-causes the linker map to be written into a file inside the directory.
-The name of the file is based upon the @var{output} filename with
-@code{.map} appended.
+@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
@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
-``missing-symbol'' or `missing-lib'' and the @var{name} of the
-missing symbol or library. The intention is that the script will
-provide suggestions to the user as to where the symbol or library
+``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.
normal dynamically linked executables they can be executed and symbols
defined in the executable cannot be overridden by shared libraries.
+@kindex -no-pie
+@item -no-pie
+@cindex position dependent executables
+Create a position dependent executable. This is the default.
+
@kindex -qmagic
@item -qmagic
This option is ignored for Linux compatibility.
libraries needed by it. The @code{DT_RPATH} entries are ignored if
@code{DT_RUNPATH} entries exist.
@item
-The default directories, normally @file{/lib} and @file{/usr/lib}.
-@item
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
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.
+Any directories specified by a @code{SEARCH_DIR} command in a
+linker script given on the command line, including scripts specified
+by @option{-T} (but not @option{-dT}).
+@item
+The default directories, normally @file{/lib} and @file{/usr/lib}.
+@item
+Any directories specified by a plugin LDPT_SET_EXTRA_LIBRARY_PATH.
+@item
+Any directories specified by a @code{SEARCH_DIR} command in a default
+linker script.
@end enumerate
+Note however on Linux based systems there is an additional caveat: If
+the @option{--as-needed} option is active @emph{and} a shared library
+is located which would normally satisfy the search @emph{and} this
+library does not have DT_NEEDED tag for @file{libc.so}
+@emph{and} there is a shared library later on in the set of search
+directories which also satisfies the search @emph{and}
+this second shared library does have a DT_NEEDED tag for
+@file{libc.so} @emph{then} the second library will be selected instead
+of the first.
+
If the required shared library is not found, the linker will issue a
warning and continue with the link.
+
@end ifset
@kindex -shared
@end smallexample
In this example, if the program defines @samp{_etext} (with a leading
-underscore), the linker will give a multiple definition error. If, on
-the other hand, the program defines @samp{etext} (with no leading
+underscore), the linker will give a multiple definition diagnostic. If,
+on the other hand, the program defines @samp{etext} (with no leading
underscore), the linker will silently use the definition in the program.
If the program references @samp{etext} but does not define it, the
linker will use the definition in the linker script.
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.
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
@item rel
@samp{R_ARM_REL32} (arm*-*-elf, arm*-*-eabi)
@item abs
-@samp{R_ARM_ABS32} (arm*-*-symbianelf)
+@samp{R_ARM_ABS32}
@item got-rel
@samp{R_ARM_GOT_PREL} (arm*-*-linux, arm*-*-*bsd)
@end table
code using BLX rather than using BX and a mode-switching stub before
each PLT entry. This should lead to such calls executing slightly faster.
-This option is enabled implicitly for SymbianOS, so there is no need to
-specify it if you are using that target.
-
@cindex VFP11_DENORM_FIX
@kindex --vfp11-denorm-fix
The @samp{--vfp11-denorm-fix} switch enables a link-time workaround for a
projects / binutils-gdb.git / blobdiff