ldのヘルプ・マニュアル／リナックスコマンド

ldのヘルプ・マニュアル

help
man

ld --help

Usage: ld [options] file... Options: -a KEYWORD Shared library control for HP/UX compatibility -A ARCH, --architecture ARCH Set architecture -b TARGET, --format TARGET Specify target for following input files -c FILE, --mri-script FILE Read MRI format linker script -d, -dc, -dp Force common symbols to be defined -e ADDRESS, --entry ADDRESS Set start address -E, --export-dynamic Export all dynamic symbols --no-export-dynamic Undo the effect of --export-dynamic -EB Link big-endian objects -EL Link little-endian objects -f SHLIB, --auxiliary SHLIB Auxiliary filter for shared object symbol table -F SHLIB, --filter SHLIB Filter for shared object symbol table -g Ignored -G SIZE, --gpsize SIZE Small data size (if no size, same as --shared) -h FILENAME, -soname FILENAME Set internal name of shared library -I PROGRAM, --dynamic-linker PROGRAM Set PROGRAM as the dynamic linker to use -l LIBNAME, --library LIBNAME Search for library LIBNAME -L DIRECTORY, --library-path DIRECTORY Add DIRECTORY to library search path --sysroot= Override the default sysroot location -m EMULATION Set emulation -M, --print-map Print map file on standard output -n, --nmagic Do not page align data -N, --omagic Do not page align data, do not make text readonly --no-omagic Page align data, make text readonly -o FILE, --output FILE Set output file name -O Optimize output file -Qy Ignored for SVR4 compatibility -q, --emit-relocs Generate relocations in final output -r, -i, --relocatable Generate relocatable output -R FILE, --just-symbols FILE Just link symbols (if directory, same as --rpath) -s, --strip-all Strip all symbols -S, --strip-debug Strip debugging symbols --strip-discarded Strip symbols in discarded sections --no-strip-discarded Do not strip symbols in discarded sections -t, --trace Trace file opens -T FILE, --script FILE Read linker script --default-script FILE, -dT Read default linker script -u SYMBOL, --undefined SYMBOL Start with undefined reference to SYMBOL --unique [=SECTION] Don't merge input [SECTION | orphan] sections -Ur Build global constructor/destructor tables -v, --version Print version information -V Print version and emulation information -x, --discard-all Discard all local symbols -X, --discard-locals Discard temporary local symbols (default) --discard-none Don't discard any local symbols -y SYMBOL, --trace-symbol SYMBOL Trace mentions of SYMBOL -Y PATH Default search path for Solaris compatibility -(, --start-group Start a group -), --end-group End a group --accept-unknown-input-arch Accept input files whose architecture cannot be determined --no-accept-unknown-input-arch Reject input files whose architecture is unknown --as-needed Only set DT_NEEDED for following dynamic libs if used --no-as-needed Always set DT_NEEDED for dynamic libraries mentioned on the command line -assert KEYWORD Ignored for SunOS compatibility -Bdynamic, -dy, -call_shared Link against shared libraries -Bstatic, -dn, -non_shared, -static Do not link against shared libraries -Bsymbolic Bind global references locally -Bsymbolic-functions Bind global function references locally --check-sections Check section addresses for overlaps (default) --no-check-sections Do not check section addresses for overlaps --copy-dt-needed-entries Copy DT_NEEDED links mentioned inside DSOs that follow --no-copy-dt-needed-entries Do not copy DT_NEEDED links mentioned inside DSOs that follow --cref Output cross reference table --defsym SYMBOL=EXPRESSION Define a symbol --demangle [=STYLE] Demangle symbol names [using STYLE] --embedded-relocs Generate embedded relocs --fatal-warnings Treat warnings as errors --no-fatal-warnings Do not treat warnings as errors (default) -fini SYMBOL Call SYMBOL at unload-time --force-exe-suffix Force generation of file with .exe suffix --gc-sections Remove unused sections (on some targets) --no-gc-sections Don't remove unused sections (default) --print-gc-sections List removed unused sections on stderr --no-print-gc-sections Do not list removed unused sections --hash-size= Set default hash table size close to --help Print option help -init SYMBOL Call SYMBOL at load-time -Map FILE Write a map file --no-define-common Do not define Common storage --no-demangle Do not demangle symbol names --no-keep-memory Use less memory and more disk I/O --no-undefined Do not allow unresolved references in object files --allow-shlib-undefined Allow unresolved references in shared libaries --no-allow-shlib-undefined Do not allow unresolved references in shared libs --allow-multiple-definition Allow multiple definitions --no-undefined-version Disallow undefined version --default-symver Create default symbol version --default-imported-symver Create default symbol version for imported symbols --no-warn-mismatch Don't warn about mismatched input files --no-warn-search-mismatch Don't warn on finding an incompatible library --no-whole-archive Turn off --whole-archive --noinhibit-exec Create an output file even if errors occur -nostdlib Only use library directories specified on the command line --oformat TARGET Specify target of output file -qmagic Ignored for Linux compatibility --reduce-memory-overheads Reduce memory overheads, possibly taking much longer --relax Relax branches on certain targets --retain-symbols-file FILE Keep only symbols listed in FILE -rpath PATH Set runtime shared library search path -rpath-link PATH Set link time shared library search path -shared, -Bshareable Create a shared library -pie, --pic-executable Create a position independent executable --sort-common [=ascending|descending] Sort common symbols by alignment [in specified order] --sort-section name|alignment Sort sections by name or maximum alignment --spare-dynamic-tags COUNT How many tags to reserve in .dynamic section --split-by-file [=SIZE] Split output sections every SIZE octets --split-by-reloc [=COUNT] Split output sections every COUNT relocs --stats Print memory usage statistics --target-help Display target specific options --task-link SYMBOL Do task level linking --traditional-format Use same format as native linker --section-start SECTION=ADDRESS Set address of named section -Tbss ADDRESS Set address of .bss section -Tdata ADDRESS Set address of .data section -Ttext ADDRESS Set address of .text section -Ttext-segment ADDRESS Set address of text segment --unresolved-symbols= How to handle unresolved symbols. is: ignore-all, report-all, ignore-in-object-files, ignore-in-shared-libs --verbose Output lots of information during link --version-script FILE Read version information script --version-exports-section SYMBOL Take export symbols list from .exports, using SYMBOL as the version. --dynamic-list-data Add data symbols to dynamic list --dynamic-list-cpp-new Use C++ operator new/delete dynamic list --dynamic-list-cpp-typeinfo Use C++ typeinfo dynamic list --dynamic-list FILE Read dynamic list --warn-common Warn about duplicate common symbols --warn-constructors Warn if global constructors/destructors are seen --warn-multiple-gp Warn if the multiple GP values are used --warn-once Warn only once per undefined symbol --warn-section-align Warn if start of section changes due to alignment --warn-shared-textrel Warn if shared object has DT_TEXTREL --warn-alternate-em Warn if an object has alternate ELF machine code --warn-unresolved-symbols Report unresolved symbols as warnings --error-unresolved-symbols Report unresolved symbols as errors --whole-archive Include all objects from following archives --wrap SYMBOL Use wrapper functions for SYMBOL @FILE Read options from FILE ld: supported targets: elf64-x86-64 elf32-i386 a.out-i386-linux pei-i386 pei-x86-64 elf64-l1om elf64-little elf64-big elf32-little elf32-big srec symbolsrec verilog tekhex binary ihex ld: supported emulations: elf_x86_64 elf_i386 i386linux elf_l1om ld: emulation specific options: elf_x86_64: --build-id[=STYLE] Generate build ID note --audit=AUDITLIB Specify a library to use for auditing -P AUDITLIB, --depaudit=AUDITLIB Specify a library to use for auditing dependencies -Bgroup Selects group name lookup rules for DSO --disable-new-dtags Disable new dynamic tags --enable-new-dtags Enable new dynamic tags --eh-frame-hdr Create .eh_frame_hdr section --hash-style=STYLE Set hash style to sysv, gnu or both -z combreloc Merge dynamic relocs into one section and sort -z defs Report unresolved symbols in object files. -z execstack Mark executable as requiring executable stack -z initfirst Mark DSO to be initialized first at runtime -z interpose Mark object to interpose all DSOs but executable -z lazy Mark object lazy runtime binding (default) -z loadfltr Mark object requiring immediate process -z muldefs Allow multiple definitions -z nocombreloc Don't merge dynamic relocs into one section -z nocopyreloc Don't create copy relocs -z nodefaultlib Mark object not to use default search paths -z nodelete Mark DSO non-deletable at runtime -z nodlopen Mark DSO not available to dlopen -z nodump Mark DSO not available to dldump -z noexecstack Mark executable as not requiring executable stack -z norelro Don't create RELRO program header -z now Mark object non-lazy runtime binding -z origin Mark object requiring immediate $ORIGIN processing at runtime -z relro Create RELRO program header -z max-page-size=SIZE Set maximum page size to SIZE -z common-page-size=SIZE Set common page size to SIZE -z KEYWORD Ignored for Solaris compatibility elf_i386: --build-id[=STYLE] Generate build ID note --audit=AUDITLIB Specify a library to use for auditing -P AUDITLIB, --depaudit=AUDITLIB Specify a library to use for auditing dependencies -Bgroup Selects group name lookup rules for DSO --disable-new-dtags Disable new dynamic tags --enable-new-dtags Enable new dynamic tags --eh-frame-hdr Create .eh_frame_hdr section --hash-style=STYLE Set hash style to sysv, gnu or both -z combreloc Merge dynamic relocs into one section and sort -z defs Report unresolved symbols in object files. -z execstack Mark executable as requiring executable stack -z initfirst Mark DSO to be initialized first at runtime -z interpose Mark object to interpose all DSOs but executable -z lazy Mark object lazy runtime binding (default) -z loadfltr Mark object requiring immediate process -z muldefs Allow multiple definitions -z nocombreloc Don't merge dynamic relocs into one section -z nocopyreloc Don't create copy relocs -z nodefaultlib Mark object not to use default search paths -z nodelete Mark DSO non-deletable at runtime -z nodlopen Mark DSO not available to dlopen -z nodump Mark DSO not available to dldump -z noexecstack Mark executable as not requiring executable stack -z norelro Don't create RELRO program header -z now Mark object non-lazy runtime binding -z origin Mark object requiring immediate $ORIGIN processing at runtime -z relro Create RELRO program header -z max-page-size=SIZE Set maximum page size to SIZE -z common-page-size=SIZE Set common page size to SIZE -z KEYWORD Ignored for Solaris compatibility elf_l1om: --build-id[=STYLE] Generate build ID note --audit=AUDITLIB Specify a library to use for auditing -P AUDITLIB, --depaudit=AUDITLIB Specify a library to use for auditing dependencies -Bgroup Selects group name lookup rules for DSO --disable-new-dtags Disable new dynamic tags --enable-new-dtags Enable new dynamic tags --eh-frame-hdr Create .eh_frame_hdr section --hash-style=STYLE Set hash style to sysv, gnu or both -z combreloc Merge dynamic relocs into one section and sort -z defs Report unresolved symbols in object files. -z execstack Mark executable as requiring executable stack -z initfirst Mark DSO to be initialized first at runtime -z interpose Mark object to interpose all DSOs but executable -z lazy Mark object lazy runtime binding (default) -z loadfltr Mark object requiring immediate process -z muldefs Allow multiple definitions -z nocombreloc Don't merge dynamic relocs into one section -z nocopyreloc Don't create copy relocs -z nodefaultlib Mark object not to use default search paths -z nodelete Mark DSO non-deletable at runtime -z nodlopen Mark DSO not available to dlopen -z nodump Mark DSO not available to dldump -z noexecstack Mark executable as not requiring executable stack -z norelro Don't create RELRO program header -z now Mark object non-lazy runtime binding -z origin Mark object requiring immediate $ORIGIN processing at runtime -z relro Create RELRO program header -z max-page-size=SIZE Set maximum page size to SIZE -z common-page-size=SIZE Set common page size to SIZE -z KEYWORD Ignored for Solaris compatibility Report bugs to

man ld

ld(1) GNU Development Tools ld(1) 名前 ld - GNU リンカ書式 ld [-o output] objfile... [-Aarchitecture] [-b input-format] [-Bstatic] [-Bdynamic] [-Bsymbolic] [-c commandfile] [--cref] [-d|-dc|-dp] [-defsym symbol = expression] [-e entry] [-embedded-relocs] [-E] [-export-dynamic] [-f name] [--auxiliary name] [-F name] [--filter name] [-format input-format] [-g] [-G size] [-h name] [-soname name] [--help] [-i] [-lar] [-Lsearchdir] [-M] [-Map mapfile] [-m emulation] [-n|-N] [-noinhibit-exec] [-no-keep-memory] [-no-warn-mismatch] [-oformat output-format] [-R filename] [-relax] [-r|-Ur] [-rpath directory] [-rpath-link directory] [-S] [-s] [-shared] [-sort-common] [-split-by-reloc count] [-split-by-file] [-T commandfile] [-Ttext textorg] [-Tdata dataorg] [-Tbss bssorg] [-t] [-u sym] [-V] [-v] [--verbose] [--version] [-warn-common] [-warn-constructors] [-warn-multiple-gp] [-warn-once] [-warn-section-align] [--whole-archive] [--no-whole-archive] [--wrap symbol] [-X] [-x] 説明 ld は複数のオブジェクトファイルや書庫 (archive) ファイルを結合し、それらのデータをリロケートして、シンボルの参照をまとめる。新たな実行プログラムをコンパイルして作成する作業の最終ステップは、多くの場合 ld の呼び出しとなる。 ld はリンカコマンド言語のファイルを受け付ける。このファイルでリンク処理を明示的に、また完全に制御することができる。この man ページではコマンド言語を説明していない。コマンド言語や GNU リンカのその他の内容に関する詳細は info の ‘ld’ エントリか、マニュアルである ld: the GNU linker を参照すること。 ld の本バージョンではオブジェクトファイル関連の作業に汎用の BFD ライブラリを用いている。これによって ld では多くの異なるフォーマットのオブジェクトファイルを読み、書き、結合することができるようになっている ( 例えば COFF や a.out)。異なるフォーマットをリンクして、あらゆる種類のオブジェクトファイルを作成できる。サポートされているフォーマットや関連するアーキテクチャに関しては ‘ objdump -i’ を実行すればよい。詳細は obj- dump(1) を見よ。 GNU リンカは柔軟であるだけでなく、診断 (diagnostic) メッセージも他のリンカより詳しい。多くのリンカはエラーが生じるとすぐに動作を停止してしまうが、 ld は可能な限り処理を続け、他のエラーに関しても知らせようとする ( あるいはエラーにもかかわらず出力ファイルを作成してしまうことさえある) 。 GNU リンカ ld は多くの状況をカバーするように作成されている。また他のリンカとできる限り互換性を保つようにしてある。したがって ld の振る舞いは、コマンドラインや環境変数によって細かく制御できるようになっている。オプションコマンドラインオプションのあまりの多さに怖気づくかもしれないが、実際の作業で指定されるオプションは、ほとんどの場合少ない。例として ld の良く用いられる例、サポートされている標準的な Unix システムで標準 Unix のオブジェクトファイルを作成する場合を考えよう。このようなシステムで hel- lo.o ファイルをリンクする作業は以下のようになる。 $ ld -o output /lib/crt0.o hello.o -lc この例では ld に output という名前のファイルを作成するように命令している。リンクするファイルは /lib/crt0.o 、 hello.o および標準的な検索ディレクトリにあるライブラリ libc.a である。 ld のコマンドラインオプションは任意の順序で指定でき、必要なだけ繰り返すことができる。オプションの繰り返しは、多くの場合最初のもの以外を無視するか、先の指定 (コマンドラインの左にあるもの) を上書きするかになる。例外 (複数回の指定が意味を持つもの) は以下の通り。 -A、-b (またはその同義である -format)、 -defsym、-L、-l、-R、-u。リンクする (複数の) オブジェクトファイルは objfile として与えるが、これはコマンドラインでオプションの後、前、あるいは混ぜて置いても構わない。ただし objfie をオプションのフラグとその引数の間に置くことはできない。通常リンカの実行には最低一つのオブジェクトファイルが指定されるが、異なるフォーマットを持つバイナリファイルを -l、-R やスクリプトコマンド言語で指定することもできる。バイナリの入力ファイルが一つも指定されない場合には、リンカは出力ファイルを作成せず、 ‘ No input files’ というメッセージを表示する。オプションの引数はオプション文字の直後にスペースなしで続けることもできるし、オプションの次に別の引数として置くこともできる。 -Aarchitecture ld のこのリリースでは、このオプションは Intel 960 アーキテクチャのファミリに対してのみ意味を持つ。このファミリ向けに設定された ld では、 architecture 引数は 960 ファミリのメンバーを示す 2 文字の名前のどれかを指定する。このオプションは出力ターゲットを指定し、入力ファイルにある非互換な命令全てに対して警告メッセージを表示する。またリンカが書庫ライブラリを検索する方法を変更し、指定されたアーキテクチャに特有のライブラリが利用できるようにする。これは検索するファイルに、アーキテクチャを示す文字列を後置したものを加えることによってなされる。例えば使用している ld のコマンドラインに -ACA または -ltry があれば、リンカは組み込みの検索パスと -L で指定されたパスを探し、以下のような名前のライブラリを見つけようとする。 try libtry.a tryca libtryca.a 最初の二つはどんな場合でも検索されるものであり、後の二つは -ACA を用いたことによって加わったものである。 ld の将来のリリースでは、同じような機能が他のアーキテクチャファミリでもサポートされる可能性がある。 -A オプションはコマンドラインで複数回用いられると、それぞれが意味を持つ。ただしアーキテクチャファミリがターゲットの組み合わせを許す場合に限られる。それぞれの指定によって、 -l で指定されたライブラリに名前のバリエーションを付けたものが検索される。 -b input-format コマンドラインでこのオプションに続いて指定された入力オブジェクトファイルのバイナリフォーマットを指定する。通常この指定は必要ない。 ld はそれぞれのマシンで最も一般的なフォーマットをデフォルトの入力フォーマットとするように設定されているからである。 input- format はテキスト文字列で、 BFD ライブラリによってサポートされている特定のフォーマットの名前である。 -format input-format はスクリプトコマンド TARGET と同じ効力を持つ。一般的なバイナリフォーマットではないファイルをリンクする場合に、このオプションを指定することになる。また異なるフォーマットのオブジェクトファイルをリンクする際に、フォーマットを明示的に変更する目的に -b を使うこともできる。この際には -b input-foramt をそれぞれのフォーマットに属するオブジェクトファイル群の前に挿入する。デフォルトのフォーマットは環境変数 GNUTARGET から取得される。スクリプトでコマンド TARGET を用いて入力フォーマットを設定することもできる。 -Bstatic 共有ライブラリに対するリンクをしない。これは共有ライブラリをサポートしているプラットフォームにおいてのみ意味を持つ。 -Bdynamic 動的ライブラリに対してリンクする。これは共有ライブラリをサポートしているプラットフォームにおいてのみ意味を持つ。そのようなプラットフォームではこのオプションは通常デフォルトになっている。 -Bsymbolic 共有ライブラリを作る場合、グローバルシンボルへの参照を共有ライブラリ内部の定義 (definition) と結合する。共有ライブラリにリンクされるプログラムでは、通常この共有ライブラリ内部の定義を上書きすることができる。このオプションが意味を持つのは共有ライブラリをサポートする ELF プラットフォームのみである。 -c commandfile commandfile からリンクコマンドを読むように ld に指示する。これらのコマンドは ld デフォルトのリンクフォーマットを完全に上書きする ( デフォルトに追加されるわけではない)。 commandfile ではターゲットフォーマットに関して必要な記述がすべてされていなければならない。リンクコマンドのスクリプトは、コマンドラインでも指定できる。これにはスクリプトの文字列をブラケット (‘{’ と ‘}’) で囲う。 --cref クロスリファレンスのテーブルを出力する。リンカのマップファイルが生成される場合には、クロスリファレンステーブルはマップファイルに出力される。それ以外の場合には標準出力に表示される。 -d -dc -dp これらの 3 つのオプションは等価である。複数の形式があるのは他のリンカとの互換性のためである。これらのいずれかを指定すると、 ld はリロケータブル出力ファイルが指定 (-r) された場合でも共通シンボルのための領域を割り当てる。スクリプトコマンド FORCE_COMMON_AL- LOCATION が同じ効力を持つ。 -defsym symbol = expression expression によって与えられた絶対アドレスを含むグローバルシンボルを出力ファイルに生成する。このオプションは必要なだけコマンドラインに指定でき、複数のシンボルを定義することができる。 expres- sion の指定には簡単な算術もサポートされている。 16 進定数や存在する他のシンボルを与えたり、 + や - をそれらの間の足し引きに用いることもできる。より手の込んだ数式が必要な場合には、スクリプトでリンカコマンド言語を用いることをすすめる。 -e entry entry をプログラムのエントリポイントを示すシンボルとして取り扱う (デフォルトのエントリポイントを上書きする)。デフォルトと他のエントリポイントの指定方法については ld の info の *Note Entry Point:: を参照すること。 -embedded-relocs このオプションが意味を持つのは GNU コンパイラやアセンブラの -membedded-pic オプションによって生成された MIPS embedded な PIC コードをリンクする場合だけである。これはリンカにテーブルを生成させる。このテーブルは、ポインタ値に対して static に初期化された全てのデータを実行時にリロケートする際に用いられる。詳細は test- suite/ld-empic 内部のコードを参照のこと。 -E -export-dynamic ELF ファイルを作成する際に、全てのシンボルをダイナミックなシンボルテーブルに追加する。通常ダイナミックシンボルテーブルには動的なオブジェクトによって用いられるシンボルのみが含まれている。このオプションは dlopen を使う場合などに必要となる。 -f name --auxiliary name ELF 共有オブジェクトを作成する際に、内部の DT_AUXILIARY フィールドを指定した名前に設定する。この指定によって、ダイナミックリンカは扱っている共有オブジェクトのシンボルテーブルを、他の共有オブジェクト name のシンボルテーブルの補助フィルタとして用いるようになる。 -F name --filter name ELF 共有オブジェクトを作成する際に、内部の DT_FILTER フィールドを指定した名前に設定する。この指定によって、ダイナミックリンカはその共有オブジェクトのシンボルテーブルを、他の共有オブジェクト name のシンボルテーブルのフィルタとして用いるようになる。 -format input-format -b input-format と同義。 -g 受け付けるが無視される。他のツールとの互換性のために用意されている。 -G size MIPS ECOFF において、 GP レジスタを用いて最適化するオブジェクトの最大サイズを size に設定する。他のオブジェクトファイルフォーマットでは無視される。 -h name -soname name ELF 共有オブジェクトを作成するとき、内部の DT_SONAME フィールドを指定した名前に設定する。実行ファイルが DT_SONAME フィールドを持つ共有オブジェクトとリンクされると、これの実行時にダイナミックリンカは DT_SONAME によって指定された共有オブジェクトをロードしようとする (通常はリンカに対して指定されたファイルをロードする) 。 --help コマンドラインオプションの要約を標準出力に表示して終了する。このオプションと --version は、他の GNU プログラムとの互換性のためダッシュ (-) 二つで始まる。これ以外のオプションは他のリンカとの互換性のためダッシュ一つで始まる。 -i インクリメンタルリンクを実行する (オプション -r と同じ)。 -lar アーカイブファイル ar をリンクするファイルのリストに加える。このオプションは何回でも指定できる。 ld は ar が指定されるごとに、 libar.a が見つかるまで検索パスを探す。 -Lsearchdir このコマンドは searchdir を ld の書庫ライブラリの検索パスに追加する。このオプションは必要なだけ指定できる。デフォルトの検索パス (-L が指定されなかったときの検索パス) は ld が用いているエミュレーションのモードに依存する。また設定に依存する場合もある。リンクスクリプトでは SEARCH_DIR コマンドを用いてこのパスを設定することもできる。 -M 標準出力にリンクマップを表示する。リンクマップには ld によってマップされたシンボルの位置情報とグローバルな共通メモリ領域の割当て情報が含まれている。 -Map mapfile ファイル mapfile にリンクマップを出力する。リンクマップには ld によってマップされたシンボルの位置情報とグローバルな共通 storage の割当て情報が含まれている。 -m emulation リンカ emulation をエミュレートする。エミュレートできるもののリストは --verbose または -V で得られる。このオプションはコンパイル時のデフォルト (ld の設定を行ったシステム向けのリンカ) を上書きする。 -N text と data セクションを読み書き可能にする。出力フォーマットが Unix スタイルのマジック・ナンバーをサポートしている場合は、出力ファイルに OMAGIC がマークされる。 -N オプションを指定するとリンカは data セグメントのページ位置調整を行わない。 -n text セグメントをリードオンリーにする。可能な場合は NMAGIC が書き込まれる。 -noinhibit-exec 通常リンカはリンク処理の途中でエラーになると出力ファイルを生成しない。このフラグをもちいると致命的でないエラーの場合には出力ファイルを残すように指定できる。 -no-keep-memory 通常リンカはメモリ消費量よりも実行速度を優先するように最適化されている。すなわち入力ファイルのシンボルテーブルがメモリにキャッシュされている。このオプションを指定すると、メモリ消費を抑えるようになる (必要に応じてシンボルテーブルを読み直す)。このオプションは大きな実行ファイルをリンクするとき、メモリを使い果たしてしまうような場合に指定する必要がある。 -no-warn-mismatch 何らかの理由でマッチしない入力ファイルをいっしょにリンクしようとすると、リンカは通常エラーになります。この原因としては、それらの入力ファイルが異なるプロセッサ用に、あるいは異なるエンディアン用にコンパイルされたなどが考えられます。このオプションを指定すると、リンカはこの種の潜在的なエラーを黙って許可します。このオプションは不用意に使うべきではありません。リンカのエラーをどうしても避けたいような、特殊な作業を行っているときに限るべきです。 -o output output は ld によって作成されるプログラムの名前である。このオプションが指定されなかった場合は a.out がデフォルトとして用いられる。スクリプトコマンド OUTPUT でも出力ファイル名を指定できる。 -oformat output-format 出力されるオブジェクトファイルのバイナリフォーマットを指定する。通常はこのオプションは必要ない。 ld でのデフォルトの出力フォーマットは、それぞれのマシンで最も普通のフォーマットになるように設定されているからである。 output-format はテキスト文字列で、 BFD ライブラリでサポートされている特定のフォーマットの名前である。スクリプトコマンド OUTPUT_FORMAT でも出力フォーマットを指定できる。しかしこのオプションはスクリプトでの指定を上書きする。 -R filename シンボル名とそれらのアドレスを filename から読み込む。しかしそれらのリロケートや出力への追加は行わない。これによって出力ファイルでは、(他のプログラムで定義された) メモリ上の絶対アドレスをシンボルを用いて参照できることになる。 -relax 機能はマシンに依存する。現在では H8/300 でのみサポートされている。プラットフォームによっては、このオプションを指定するとグローバルな最適化を行う場合もある。これはリンカがプログラムのアドレスを置き換える (出力されるオブジェクトファイルのアドレスモードを relax させたり新しい命令を同期させる) 場合に可能となる。サポートされていないプラットフォームでは、 -relax は受け付けられるが何も起こらない。 -r リロケータブルな出力を生成する。すなわち再び ld の入力として用いることができるようなファイルを生成する。これはしばしば部分 (par- tial) リンクと呼ばれる。また標準 Unix のマジック・ナンバーをサポートする環境では、このオプションは出力ファイルのマジック・ナンバーを OMAGIC にする。このオプションが指定されなかった場合は、完全なファイルが生成される。 C++ プログラムをリンクする場合、このオプションはコンストラクタへの参照を解決しない。 C++ の場合には代わりに -Ur を用いることができる。このオプションは -i と同じ。 -rpath directory ディレクトリを実行時ライブラリの検索パスに追加する。これは ELF の実行ファイルを共有オブジェクトとリンクするときに用いられる。 -rpath の引き数は全て結合され、ダイナミックリンカに渡される。ダイナミックリンカは、これを用いてロードする共有オブジェクトを実行時に決定する。 -rpath オプションはリンクに明示的に含まれている共有オブジェクトによって必要とされる別の共有オブジェクトを指定するのに用いることもできる。 -rpath-link オプションの説明を見よ。 ELF 実行ファイルの -rpath が指定されない場合には、 (指定されていれば) 環境変数 LD_RUN_PATH の値が用いられる。 -rpath オプションは SunOS で用いることもできる。 SunOS のデフォルトでは、リンカは実行時の検索パスを -L オプションで与えられたパスから生成する。 -rpath が用いられると、実行時の検索パスは -rpath オプションで与えられたパスのみから生成され、 -L オプションは無視される。これは gcc を使っていて、 -L がたくさん指定されてしまう (これらは NFS マウントされたファイルシステムかもしれない) 場合などに便利である。 -rpath-link directory ELF か SunOS を用いている場合、ある共有ライブラリが別の共有ライブラリを必要とする場合がある。これは ld -shared によるリンクで入力ファイルに共有ライブラリが含まれている場合に起こる。リンカが非共有 (非リロケータブル) なリンクを行っているときに、このような依存関係に遭遇すると、リンカは自動的にその必要とされている共有ライブラリも (明示されていなくても) リンクしてしまおうとする。このような場合に -rpath-link オプションは検索する最初のディレクトリセットを指定する。 -rpath-link オプションではディレクトリ名の並びをコロンで区切って一度に指定することもできるし、複数回用いて指定することもできる。必要な共有ライブラリが見つからないと、リンカは警告を出してリンク処理を継続しようとする。 -S 出力ファイルからデバッガのシンボル情報を削除する (全てのシンボルではない)。 -s 出力ファイルから全てのシンボル情報を削除する。 -shared 共有ライブラリを生成する。現在のところ ELF と SunOS プラットフォームでのみサポートされている (実際には SunOS では不要である。なぜならリンカは未定義シンボルが存在していたり -e オプションが指定されている場合には自動的に共有ライブラリを生成するからである)。 -sort-common 通常 ld がグローバルな共通シンボルをそれぞれの出力セクションに配置するにあたっては、それらはサイズによってソートされる。まず 1 バイト変数のシンボル、ついで 2 バイト、 4 バイト変数のシンボル、最後にそれ以外のものが並ぶ。このオプションはアラインメントによって生じてしまうシンボル間のギャップを防止する。このオプションはソートを行わないようにする。 -split-by-reloc count 出力ファイルに余分なセクションを生成して、ファイル中のそれぞれの出力セクションが count 以上のリロケーションを含まないようにする。これは COFF オブジェクトファイルフォーマットの巨大なリロケータブルファイルを、リアルタイムカーネルにダウンロードする場合などに役に立つ。 COFF はセクションあたり 65535 以上のリロケーションを持てないからである。任意のセクションをサポートしていないフォーマットでは、このオプションは機能しないことに注意。リンカはそれぞれの入力セクションを分割して再配置するわけではない。したがって入力ファイルのセクションに count 以上のリロケーションを含むものがあれば、それに対応してそれだけのリロケーションを持った出力セクションは作成されてしまう。 -split-by-file -split-by-reloc と似ているが、それぞれの入力ファイルに対して新たな出力セクションを生成する。 -Tbss org -Tdata org -Ttext org それぞれ出力ファイルの bss、 data、 text セグメントに対して org を開始アドレスにする。 org は 16 進の整数でなければならない。 -T commandfile -c commandfile と等価である。他のツールとの互換性のために用意された。 -t 入力ファイルを ld が処理するごとに、ファイルの名前を表示する。 -u sym sym を出力ファイルに未定義なシンボルとして挿入する。例えばこれは、標準ライブラリから付加的なモジュールをリンクするトリガに使うことができる。 -u は必要な未定義シンボルの数だけ繰り返すことができる。 -Ur C++ プログラム以外では、このオプションは -r と等価であり、リロケータブルな出力を生成する (つまり再び ld の入力ファイルに用いることのできるファイルを出力する)。 C++ プログラムをリンクする際には、 -Ur は -r と異なり、コンストラクタへの参照を解決する。 --verbose ld のバージョン番号を表示し、サポートされているエミュレーションをリストする。入力ファイルがそれぞれオープンできるかどうかも表示する。 -v, -V ld のバージョン番号を表示する。 -V はサポートされているエミュレーションもリストする。 --version ld のバージョン番号を表示して終了する。 -warn-common 共通シンボルが他の共通シンボルやシンボル定義と結合されている場合に警告を発する。 Unix のリンカはこの点には比較的寛容であるが、他の OS のリンカにはそうでないものもある。このオプションはグローバルシンボルを結合することによって生じる問題点を見つける手がかりになるかもしれない。 -warn-constructors グローバルコンストラクタが用いられたら警告を発する。これが意味を持つオブジェクトファイルフォーマットは少ない。 COFF や ELF では、リンカはグローバルコンストラクタを検出することができない。 -warn-multiple-gp 出力ファイルに複数のグローバルなポインタ値が必要な場合に警告を発する。このオプションが意味を持つのは、 Alpha のような特殊なプロセッサだけである。 -warn-once 未定義シンボルに関する警告をシンボルごとに一度だけにする。デフォルトではそのシンボルを参照するモジュール一つについて一回警告が出る。 -warn-section-align 出力セクションのアドレスがアラインメントのために変更された場合に警告を出す。通常アラインメントは入力セクションによって設定される。アドレスは明示的に指定されなかった場合 (つまり SECTIONS コマンドがセクションのスタートアドレスを指定しなかった場合) にのみ変更されうる。 --whole-archive コマンドラインでこのオプション以降に指定されたそれぞれの書庫に対して、書庫内部の全てのオブジェクトファイルをリンクする (デフォルトでは書庫から必要なオブジェクトファイルを検索する)。これは通常書庫ファイルを共有ライブラリに変えるとき、内部のオブジェクトを全て共有ライブラリに含めるために指定される。 --no-whole-archive コマンドラインでこのオプション以降に現われる書庫に対して --whole-archive オプションの効果を無効にする。 --wrap symbol symbol に対してラッパ機能を用いる。 symbol への未定義な参照は全て __wrap_symbol として解決される。また __REAL_symbol への未定義な参照はすべて symbol として解決される。 -X 一時的なローカルシンボルをすべて削除する。ほとんどのターゲットでは、これは ‘L’ で始まるローカルシンボルを意味する。 -x ローカルシンボルを全て削除する。環境変数 ld の動作は環境変数 GNUTARGET によって変更することができる。 GNUTARGET は -b (または等価なオプション -format) を用いない場合の入力ファイルのオブジェクトフォーマットを定義する。この値は入力フォーマットに対して有効な BFD 名の一つでなければならない。 GNUTARGET が default に設定されていた場合には、 BFD は入力されるバイナリファイルを調べて入力フォーマットを決定しようとする。これは通常は成功するが、決定できない可能性もある。オブジェクトファイルフォーマットで用いられているマジック・ナンバーが一意であることを保証する方法は存在しないからである。しかし BFD をそれぞれのシステムで設定する際には、そのシステムに一般的なフォーマットが検索リストの最初の方に置かれる。したがって複数フォーマットの可能性が存在した場合には、より一般的なフォーマットとして解釈される。関連項目 objdump(1) info の ‘ld’ および ‘binutils’ エントリ ld: the GNU linker , Steve Chamberlain and Roland Pesch; The GNU Binary Utilities , Roland H. Pesch 著作権 Copyright (c) 1991, 1992 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the en- tire resulting derived work is distributed under the terms of a permis- sion notice identical to this one. Permission is granted to copy and distribute translations of this manu- al into another language, under the above conditions for modified ver- sions, except that this permission notice may be included in transla- tions approved by the Free Software Foundation instead of in the origi- nal English. cygnus support 17 August 1992 ld(1)

LD(1) GNU Development Tools LD(1) NAME ld - The GNU linker SYNOPSIS ld [options] objfile ... DESCRIPTION ld combines a number of object and archive files, relocates their data and ties up symbol references. Usually the last step in compiling a program is to run ld. ld accepts Linker Command Language files written in a superset of AT&T’s Link Editor Command Language syntax, to provide explicit and total control over the linking process. This man page does not describe the command language; see the ld entry in "info" for full details on the command language and on other aspects of the GNU linker. This version of ld uses the general purpose BFD libraries to operate on object files. This allows ld to read, combine, and write object files in many different formats---for example, COFF or "a.out". Different formats may be linked together to produce any available kind of object file. Aside from its flexibility, the GNU linker is more helpful than other linkers in providing diagnostic information. Many linkers abandon execution immediately upon encountering an error; whenever possible, ld continues executing, allowing you to identify other errors (or, in some cases, to get an output file in spite of the error). The GNU linker ld is meant to cover a broad range of situations, and to be as compatible as possible with other linkers. As a result, you have many choices to control its behavior. OPTIONS The linker supports a plethora of command-line options, but in actual practice few of them are used in any particular context. For instance, a frequent use of ld is to link standard Unix object files on a standard, supported Unix system. On such a system, to link a file "hello.o": ld -o /lib/crt0.o hello.o -lc This tells ld to produce a file called output as the result of linking the file "/lib/crt0.o" with "hello.o" and the library "libc.a", which will come from the standard search directories. (See the discussion of the -l option below.) Some of the command-line options to ld may be specified at any point in the command line. However, options which refer to files, such as -l or -T, cause the file to be read at the point at which the option appears in the command line, relative to the object files and other file options. Repeating non-file options with a different argument will either have no further effect, or override prior occurrences (those further to the left on the command line) of that option. Options which may be meaningfully specified more than once are noted in the descriptions below. Non-option arguments are object files or archives which are to be linked together. They may follow, precede, or be mixed in with command-line options, except that an object file argument may not be placed between an option and its argument. Usually the linker is invoked with at least one object file, but you can specify other forms of binary input files using -l, -R, and the script command language. If no binary input files at all are specified, the linker does not produce any output, and issues the message No input files. If the linker cannot recognize the format of an object file, it will assume that it is a linker script. A script specified in this way augments the main linker script used for the link (either the default linker script or the one specified by using -T). This feature permits the linker to link against a file which appears to be an object or an archive, but actually merely defines some symbol values, or uses "INPUT" or "GROUP" to load other objects. Specifying a script in this way merely augments the main linker script, with the extra commands placed after the main script; use the -T option to replace the default linker script entirely, but note the effect of the "INSERT" command. For options whose names are a single letter, option arguments must either follow the option letter without intervening whitespace, or be given as separate arguments immediately following the option that requires them. For options whose names are multiple letters, either one dash or two can precede the option name; for example, -trace-symbol and --trace-symbol are equivalent. Note---there is one exception to this rule. Multiple letter options that start with a lower case ’o’ can only be preceded by two dashes. This is to reduce confusion with the -o option. So for example -omagic sets the output file name to magic whereas --omagic sets the NMAGIC flag on the output. Arguments to multiple-letter options must either be separated from the option name by an equals sign, or be given as separate arguments immediately following the option that requires them. For example, --trace-symbol foo and --trace-symbol=foo are equivalent. Unique abbreviations of the names of multiple-letter options are accepted. Note---if the linker is being invoked indirectly, via a compiler driver (e.g. gcc) then all the linker command line options should be prefixed by -Wl, (or whatever is appropriate for the particular compiler driver) like this: gcc -Wl,--start-group foo.o bar.o -Wl,--end-group This is important, because otherwise the compiler driver program may silently drop the linker options, resulting in a bad link. Confusion may also arise when passing options that require values through a driver, as the use of a space between option and argument acts as a separator, and causes the driver to pass only the option to the linker and the argument to the compiler. In this case, it is simplest to use the joined forms of both single- and multiple-letter options, such as: gcc foo.o bar.o -Wl,-eENTRY -Wl,-Map=a.map Here is a table of the generic command line switches accepted by the GNU linker: @file Read command-line options from file. The options read are inserted in place of the original @file option. If file does not exist, or cannot be read, then the option will be treated literally, and not removed. Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional @file options; any such options will be processed recursively. -a keyword This option is supported for HP/UX compatibility. The keyword argument must be one of the strings archive, shared, or default. -aarchive is functionally equivalent to -Bstatic, and the other two keywords are functionally equivalent to -Bdynamic. This option may be used any number of times. --audit AUDITLIB Adds AUDITLIB to the "DT_AUDIT" entry of the dynamic section. AUDITLIB is not checked for existence, nor will it use the DT_SONAME specified in the library. If specified multiple times "DT_AUDIT" will contain a colon separated list of audit interfaces to use. If the linker finds an object with an audit entry while searching for shared libraries, it will add a corresponding "DT_DEPAUDIT" entry in the output file. This option is only meaningful on ELF platforms supporting the rtld-audit interface. -A architecture --architecture=architecture In the current release of ld, this option is useful only for the Intel 960 family of architectures. In that ld configuration, the architecture argument identifies the particular architecture in the 960 family, enabling some safeguards and modifying the archive- library search path. Future releases of ld may support similar functionality for other architecture families. -b input-format --format=input-format ld may be configured to support more than one kind of object file. If your ld is configured this way, you can use the -b option to specify the binary format for input object files that follow this option on the command line. Even when ld is configured to support alternative object formats, you don’t usually need to specify this, as ld should be configured to expect as a default input format the most usual format on each machine. input-format is a text string, the name of a particular format supported by the BFD libraries. (You can list the available binary formats with objdump -i.) You may want to use this option if you are linking files with an unusual binary format. You can also use -b to switch formats explicitly (when linking object files of different formats), by including -b input-format before each group of object files in a particular format. The default format is taken from the environment variable "GNUTARGET". You can also define the input format from a script, using the command "TARGET"; -c MRI-commandfile --mri-script=MRI-commandfile For compatibility with linkers produced by MRI, ld accepts script files written in an alternate, restricted command language, described in the MRI Compatible Script Files section of GNU ld documentation. Introduce MRI script files with the option -c; use the -T option to run linker scripts written in the general-purpose ld scripting language. If MRI-cmdfile does not exist, ld looks for it in the directories specified by any -L options. -d -dc -dp These three options are equivalent; multiple forms are supported for compatibility with other linkers. They assign space to common symbols even if a relocatable output file is specified (with -r). The script command "FORCE_COMMON_ALLOCATION" has the same effect. --depaudit AUDITLIB -P AUDITLIB Adds AUDITLIB to the "DT_DEPAUDIT" entry of the dynamic section. AUDITLIB is not checked for existence, nor will it use the DT_SONAME specified in the library. If specified multiple times "DT_DEPAUDIT" will contain a colon separated list of audit interfaces to use. This option is only meaningful on ELF platforms supporting the rtld-audit interface. The -P option is provided for Solaris compatibility. -e entry --entry=entry Use entry as the explicit symbol for beginning execution of your program, rather than the default entry point. If there is no symbol named entry, the linker will try to parse entry as a number, and use that as the entry address (the number will be interpreted in base 10; you may use a leading 0x for base 16, or a leading 0 for base 8). --exclude-libs lib,lib,... Specifies a list of archive libraries from which symbols should not be automatically exported. The library names may be delimited by commas or colons. Specifying "--exclude-libs ALL" excludes symbols in all archive libraries from automatic export. This option is available only for the i386 PE targeted port of the linker and for ELF targeted ports. For i386 PE, symbols explicitly listed in a .def file are still exported, regardless of this option. For ELF targeted ports, symbols affected by this option will be treated as hidden. --exclude-modules-for-implib module,module,... Specifies a list of object files or archive members, from which symbols should not be automatically exported, but which should be copied wholesale into the import library being generated during the link. The module names may be delimited by commas or colons, and must match exactly the filenames used by ld to open the files; for archive members, this is simply the member name, but for object files the name listed must include and match precisely any path used to specify the input file on the linker’s command-line. This option is available only for the i386 PE targeted port of the linker. Symbols explicitly listed in a .def file are still exported, regardless of this option. -E --export-dynamic --no-export-dynamic When creating a dynamically linked executable, using the -E option or the --export-dynamic option causes the linker to add all symbols to the dynamic symbol table. The dynamic symbol table is the set of symbols which are visible from dynamic objects at run time. If you do not use either of these options (or use the --no-export-dynamic option to restore the default behavior), the dynamic symbol table will normally contain only those symbols which are referenced by some dynamic object mentioned in the link. If you use "dlopen" to load a dynamic object which needs to refer back to the symbols defined by the program, rather than some other dynamic object, then you will probably need to use this option when linking the program itself. You can also use the dynamic list to control what symbols should be added to the dynamic symbol table if the output format supports it. See the description of --dynamic-list. Note that this option is specific to ELF targeted ports. PE targets support a similar function to export all symbols from a DLL or EXE; see the description of --export-all-symbols below. -EB Link big-endian objects. This affects the default output format. -EL Link little-endian objects. This affects the default output format. -f name --auxiliary=name When creating an ELF shared object, set the internal DT_AUXILIARY field to the specified name. This tells the dynamic linker that the symbol table of the shared object should be used as an auxiliary filter on the symbol table of the shared object name. If you later link a program against this filter object, then, when you run the program, the dynamic linker will see the DT_AUXILIARY field. If the dynamic linker resolves any symbols from the filter object, it will first check whether there is a definition in the shared object name. If there is one, it will be used instead of the definition in the filter object. The shared object name need not exist. Thus the shared object name may be used to provide an alternative implementation of certain functions, perhaps for debugging or for 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. -F name --filter=name When creating an ELF shared object, set the internal DT_FILTER field to the specified name. This tells the dynamic linker that the symbol table of the shared object which is being created should be used as a filter on the symbol table of the shared object name. If you later link a program against this filter object, then, when you run the program, the dynamic linker will see the DT_FILTER field. The dynamic linker will resolve symbols according to the symbol table of the filter object as usual, but it will actually link to the definitions found in the shared object name. Thus the filter object can be used to select a subset of the symbols provided by the object name. Some older linkers used the -F option throughout a compilation toolchain for specifying object-file format for both input and output object files. The GNU linker uses other mechanisms for this purpose: the -b, --format, --oformat options, the "TARGET" command in linker scripts, and the "GNUTARGET" environment variable. The GNU linker will ignore the -F option when not creating an ELF shared object. -fini=name When creating an ELF executable or shared object, call NAME when the executable or shared object is unloaded, by setting DT_FINI to the address of the function. By default, the linker uses "_fini" as the function to call. -g Ignored. Provided for compatibility with other tools. -G value --gpsize=value Set the maximum size of objects to be optimized using the GP register to size. This is only meaningful for object file formats such as MIPS ECOFF which supports putting large and small objects into different sections. This is ignored for other object file formats. -h name -soname=name When creating an ELF shared object, set the internal DT_SONAME field to the specified name. When an executable is linked with a shared object which has a DT_SONAME field, then when the executable is run the dynamic linker will attempt to load the shared object specified by the DT_SONAME field rather than the using the file name given to the linker. -i Perform an incremental link (same as option -r). -init=name When creating an ELF executable or shared object, call NAME when the executable or shared object is loaded, by setting DT_INIT to the address of the function. By default, the linker uses "_init" as the function to call. -l namespec --library=namespec Add the archive or object file specified by namespec to the list of files to link. This option may be used any number of times. If namespec is of the form :filename, ld will search the library path for a file called filename, otherwise it will search the library path for a file called libnamespec.a. On systems which support shared libraries, ld may also search for files other than libnamespec.a. Specifically, on ELF and SunOS systems, ld will search a directory for a library called libnamespec.so before searching for one called libnamespec.a. (By convention, a ".so" extension indicates a shared library.) Note that this behavior does not apply to :filename, which always specifies a file called filename. The linker will search an archive only once, at the location where it is specified on the command line. If the archive defines a symbol which was undefined in some object which appeared before the archive on the command line, the linker will include the appropriate file(s) from the archive. However, an undefined symbol in an object appearing later on the command line will not cause the linker to search the archive again. See the -( option for a way to force the linker to search archives multiple times. You may list the same archive multiple times on the command line. This type of archive searching is standard for Unix linkers. However, if you are using ld on AIX, note that it is different from the behaviour of the AIX linker. -L searchdir --library-path=searchdir Add path searchdir to the list of paths that ld will search for archive libraries and ld control scripts. You may use this option any number of times. The directories are searched in the order in which they are specified on the command line. Directories specified on the command line are searched before the default directories. All -L options apply to all -l options, regardless of the order in which the options appear. -L options do not affect how ld searches for a linker script unless -T option is specified. If searchdir begins with "=", then the "=" will be replaced by the sysroot prefix, a path specified when the linker is configured. The default set of paths searched (without being specified with -L) depends on which emulation mode ld is using, and in some cases also on how it was configured. The paths can also be specified in a link script with the "SEARCH_DIR" command. Directories specified this way are searched at the point in which the linker script appears in the command line. -m emulation Emulate the emulation linker. You can list the available emulations with the --verbose or -V options. If the -m option is not used, the emulation is taken from the "LDEMULATION" environment variable, if that is defined. Otherwise, the default emulation depends upon how the linker was configured. -M --print-map Print a link map to the standard output. A link map provides information about the link, including the following: · Where object files are mapped into memory. · How common symbols are allocated. · All archive members included in the link, with a mention of the symbol which caused the archive member to be brought in. · The values assigned to symbols. Note - symbols whose values are computed by an expression which involves a reference to a previous value of the same symbol may not have correct result displayed in the link map. This is because the linker discards intermediate results and only retains the final value of an expression. Under such circumstances the linker will display the final value enclosed by square brackets. Thus for example a linker script containing: foo = 1 foo = foo * 4 foo = foo + 8 will produce the following output in the link map if the -M option is used: 0x00000001 foo = 0x1 [0x0000000c] foo = (foo * 0x4) [0x0000000c] foo = (foo + 0x8) See Expressions for more information about expressions in linker scripts. -n --nmagic Turn off page alignment of sections, and mark the output as "NMAGIC" if possible. -N --omagic Set the text and data sections to be readable and writable. Also, do not page-align the data segment, and disable linking against shared libraries. If the output format supports Unix style magic numbers, mark the output as "OMAGIC". Note: Although a writable text section is allowed for PE-COFF targets, it does not conform to the format specification published by Microsoft. --no-omagic This option negates most of the effects of the -N option. It sets the text section to be read-only, and forces the data segment to be page-aligned. Note - this option does not enable linking against shared libraries. Use -Bdynamic for this. -o output --output=output Use output as the name for the program produced by ld; if this option is not specified, the name a.out is used by default. The script command "OUTPUT" can also specify the output file name. -O level If level is a numeric values greater than zero ld optimizes the output. This might take significantly longer and therefore probably should only be enabled for the final binary. At the moment this option only affects ELF shared library generation. Future releases of the linker may make more use of this option. Also currently there is no difference in the linker’s behaviour for different non-zero values of this option. Again this may change with future releases. -q --emit-relocs Leave relocation sections and contents in fully linked executables. Post link analysis and optimization tools may need this information in order to perform correct modifications of executables. This results in larger executables. This option is currently only supported on ELF platforms. --force-dynamic Force the output file to have dynamic sections. This option is specific to VxWorks targets. -r --relocatable Generate relocatable output---i.e., generate an output file that can in turn serve as input to ld. This is often called partial linking. As a side effect, in environments that support standard Unix magic numbers, this option also sets the output file’s magic number to "OMAGIC". If this option is not specified, an absolute file is produced. When linking C++ programs, this option will not resolve references to constructors; to do that, use -Ur. When an input file does not have the same format as the output file, partial linking is only supported if that input file does not contain any relocations. Different output formats can have further restrictions; for example some "a.out"-based formats do not support partial linking with input files in other formats at all. This option does the same thing as -i. -R filename --just-symbols=filename Read symbol names and their addresses from filename, but do not relocate it or include it in the output. This allows your output file to refer symbolically to absolute locations of memory defined in other programs. You may use this option more than once. For compatibility with other ELF linkers, if the -R option is followed by a directory name, rather than a file name, it is treated as the -rpath option. -s --strip-all Omit all symbol information from the output file. -S --strip-debug Omit debugger symbol information (but not all symbols) from the output file. -t --trace Print the names of the input files as ld processes them. -T scriptfile --script=scriptfile Use scriptfile as the linker script. This script replaces ld’s default linker script (rather than adding to it), so commandfile must specify everything necessary to describe the output file. If scriptfile does not exist in the current directory, "ld" looks for it in the directories specified by any preceding -L options. Multiple -T options accumulate. -dT scriptfile --default-script=scriptfile Use scriptfile as the default linker script. This option is similar to the --script option except that processing of the script is delayed until after the rest of the command line has been processed. This allows options placed after the --default-script option on the command line to affect the behaviour of the linker script, which can be important when the linker command line cannot be directly controlled by the user. (eg because the command line is being constructed by another tool, such as gcc). -u symbol --undefined=symbol Force symbol to be entered in the output file as an undefined symbol. Doing this may, for example, trigger linking of additional modules from standard libraries. -u may be repeated with different option arguments to enter additional undefined symbols. This option is equivalent to the "EXTERN" linker script command. -Ur For anything other than C++ programs, this option is equivalent to -r: it generates relocatable output---i.e., an output file that can in turn serve as input to ld. When linking C++ programs, -Ur does resolve references to constructors, unlike -r. It does not work to use -Ur on files that were themselves linked with -Ur; once the constructor table has been built, it cannot be added to. Use -Ur only for the last partial link, and -r for the others. --unique[=SECTION] Creates a separate output section for every input section matching SECTION, or if the optional wildcard SECTION argument is missing, for every orphan input section. An orphan section is one not specifically mentioned in a linker script. You may use this option multiple times on the command line; It prevents the normal merging of input sections with the same name, overriding output section assignments in a linker script. -v --version -V Display the version number for ld. The -V option also lists the supported emulations. -x --discard-all Delete all local symbols. -X --discard-locals Delete all temporary local symbols. (These symbols start with system-specific local label prefixes, typically .L for ELF systems or L for traditional a.out systems.) -y symbol --trace-symbol=symbol Print the name of each linked file in which symbol appears. This option may be given any number of times. On many systems it is necessary to prepend an underscore. This option is useful when you have an undefined symbol in your link but don’t know where the reference is coming from. -Y path Add path to the default library search path. This option exists for Solaris compatibility. -z keyword The recognized keywords are: combreloc Combines multiple reloc sections and sorts them to make dynamic symbol lookup caching possible. defs Disallows undefined symbols in object files. Undefined symbols in shared libraries are still allowed. execstack Marks the object as requiring executable stack. initfirst This option is only meaningful when building a shared object. It marks the object so that its runtime initialization will occur before the runtime initialization of any other objects brought into the process at the same time. Similarly the runtime finalization of the object will occur after the runtime finalization of any other objects. interpose Marks the object that its symbol table interposes before all symbols but the primary executable. lazy When generating an executable or shared library, mark it to tell the dynamic linker to defer function call resolution to the point when the function is called (lazy binding), rather than at load time. Lazy binding is the default. loadfltr Marks the object that its filters be processed immediately at runtime. muldefs Allows multiple definitions. nocombreloc Disables multiple reloc sections combining. nocopyreloc Disables production of copy relocs. nodefaultlib Marks the object that the search for dependencies of this object will ignore any default library search paths. nodelete Marks the object shouldn’t be unloaded at runtime. nodlopen Marks the object not available to "dlopen". nodump Marks the object can not be dumped by "dldump". noexecstack Marks the object as not requiring executable stack. norelro Don’t create an ELF "PT_GNU_RELRO" segment header in the object. now When generating an executable or shared library, mark it to tell the dynamic linker to resolve all symbols when the program is started, or when the shared library is linked to using dlopen, instead of deferring function call resolution to the point when the function is first called. origin Marks the object may contain $ORIGIN. relro Create an ELF "PT_GNU_RELRO" segment header in the object. max-page-size=value Set the emulation maximum page size to value. common-page-size=value Set the emulation common page size to value. Other keywords are ignored for Solaris compatibility. -( archives -) --start-group archives --end-group The archives should be a list of archive files. They may be either explicit file names, or -l options. The specified archives are searched repeatedly until no new undefined references are created. Normally, an archive is searched only once in the order that it is specified on the command line. If a symbol in that archive is needed to resolve an undefined symbol referred to by an object in an archive that appears later on the command line, the linker would not be able to resolve that reference. By grouping the archives, they all be searched repeatedly until all possible references are resolved. Using this option has a significant performance cost. It is best to use it only when there are unavoidable circular references between two or more archives. --accept-unknown-input-arch --no-accept-unknown-input-arch Tells the linker to accept input files whose architecture cannot be recognised. The assumption is that the user knows what they are doing and deliberately wants to link in these unknown input files. This was the default behaviour of the linker, before release 2.14. The default behaviour from release 2.14 onwards is to reject such input files, and so the --accept-unknown-input-arch option has been added to restore the old behaviour. --as-needed --no-as-needed This option affects ELF DT_NEEDED tags for dynamic libraries mentioned on the command line after the --as-needed option. Normally 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. --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. --no-as-needed restores the default behaviour. --add-needed --no-add-needed These two options have been deprecated because of the similarity of their names to the --as-needed and --no-as-needed options. They have been replaced by --copy-dt-needed-entries and --no-copy-dt-needed-entries. -assert keyword This option is ignored for SunOS compatibility. -Bdynamic -dy -call_shared Link against dynamic libraries. This is only meaningful on platforms for which shared libraries are supported. This option is normally the default on such platforms. The different variants of this option are for compatibility with various systems. You may use this option multiple times on the command line: it affects library searching for -l options which follow it. -Bgroup Set the "DF_1_GROUP" flag in the "DT_FLAGS_1" entry in the dynamic section. This causes the runtime linker to handle lookups in this object and its dependencies to be performed only inside the group. --unresolved-symbols=report-all is implied. This option is only meaningful on ELF platforms which support shared libraries. -Bstatic -dn -non_shared -static Do not link against shared libraries. This is only meaningful on platforms for which shared libraries are supported. The different variants of this option are for compatibility with various systems. You may use this option multiple times on the command line: it affects library searching for -l options which follow it. This option also implies --unresolved-symbols=report-all. This option can be used with -shared. Doing so means that a shared library is being created but that all of the library’s external references must be resolved by pulling in entries from static libraries. -Bsymbolic 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. -Bsymbolic-functions When creating a shared library, bind references to global function symbols to the definition within the shared library, if any. This option is only meaningful on ELF platforms which support shared libraries. --dynamic-list=dynamic-list-file Specify the name of a dynamic list file to the linker. This is typically used when creating shared libraries to specify a list of global symbols whose references shouldn’t be bound to the definition within the shared library, or creating dynamically linked executables to specify a list of symbols which should be added to the symbol table in the executable. This option is only meaningful on ELF platforms which support shared libraries. The format of the dynamic list is the same as the version node without scope and node name. See VERSION for more information. --dynamic-list-data Include all global data symbols to the dynamic list. --dynamic-list-cpp-new Provide the builtin dynamic list for C++ operator new and delete. It is mainly useful for building shared libstdc++. --dynamic-list-cpp-typeinfo Provide the builtin dynamic list for C++ runtime type identification. --check-sections --no-check-sections Asks the linker not to check section addresses after they have been assigned to see if there are any overlaps. Normally the linker will perform this check, and if it finds any overlaps it will produce suitable error messages. The linker does know about, and does make allowances for sections in overlays. The default behaviour can be restored by using the command line switch --check-sections. Section overlap is not usually checked for relocatable links. You can force checking in that case by using the --check-sections option. --copy-dt-needed-entries --no-copy-dt-needed-entries This option affects the treatment of dynamic libraries referred to by DT_NEEDED tags inside ELF dynamic libraries mentioned on the command line. Normally the linker will add a DT_NEEDED tag to the output binary for each library mentioned in a DT_NEEDED tag in an input dynamic library. With --no-copy-dt-needed-entries specified on the command line however any dynamic libraries that follow it will have their DT_NEEDED entries ignored. The default behaviour can be restored with --copy-dt-needed-entries. This option also has an effect on the resolution of symbols in dynamic libraries. With the default setting dynamic libraries mentioned on the command line will be recursively searched, following their DT_NEEDED tags to other libraries, in order to resolve symbols required by the output binary. With --no-copy-dt-needed-entries specified however the searching of dynamic libraries that follow it will stop with the dynamic library itself. No DT_NEEDED links will be traversed to resolve symbols. --cref Output a cross reference table. If a linker map file is being generated, the cross reference table is printed to the map file. Otherwise, it is printed on the standard output. The format of the table is intentionally simple, so that it may be 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. --no-define-common This option inhibits the assignment of addresses to common symbols. The script command "INHIBIT_COMMON_ALLOCATION" has the same effect. The --no-define-common option allows decoupling the decision to assign addresses to Common symbols from the choice of the output file type; otherwise a non-Relocatable output type forces assigning addresses to Common symbols. Using --no-define-common allows Common symbols that are referenced from a shared library to be assigned addresses only in the main program. This eliminates the unused duplicate space in the shared library, and also prevents any possible confusion over resolving to the wrong duplicate when there are many dynamic modules with specialized search paths for runtime symbol resolution. --defsym=symbol=expression Create a global symbol in the output file, containing the absolute address given by expression. You may use this option as many times as necessary to define multiple symbols in the command line. A limited form of arithmetic is supported for the expression in this context: you may give a hexadecimal constant or the name of an existing symbol, or use "+" and "-" to add or subtract hexadecimal constants or symbols. If you need more elaborate expressions, consider using the linker command language from a script. Note: there should be no white space between symbol, the equals sign ("="), and expression. --demangle[=style] --no-demangle These options control whether to demangle symbol names in error messages and other output. When the linker is told to demangle, it tries to present symbol names in a readable fashion: it strips leading underscores if they are used by the object file format, and converts C++ mangled symbol names into user readable names. Different compilers have different mangling styles. The optional demangling style argument can be used to choose an appropriate demangling style for your compiler. The linker will demangle by default unless the environment variable COLLECT_NO_DEMANGLE is set. These options may be used to override the default. -Ifile --dynamic-linker=file Set the name of the dynamic linker. This is only meaningful when generating dynamically linked ELF executables. The default dynamic linker is normally correct; don’t use this unless you know what you are doing. --fatal-warnings --no-fatal-warnings Treat all warnings as errors. The default behaviour can be restored with the option --no-fatal-warnings. --force-exe-suffix Make sure that an output file has a .exe suffix. If a successfully built fully linked output file does not have a ".exe" or ".dll" suffix, this option forces the linker to copy the output file to one of the same name with a ".exe" suffix. This option is useful when using unmodified Unix makefiles on a Microsoft Windows host, since some versions of Windows won’t run an image unless it ends in a ".exe" suffix. --gc-sections --no-gc-sections 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 --no-gc-sections on the command line. --gc-sections decides which input sections are used by examining symbols and relocations. The section containing the entry symbol and all sections containing symbols undefined on the command-line will be kept, as will sections containing symbols referenced by dynamic objects. Note that when building shared libraries, the linker must assume that any visible symbol is referenced. Once this initial set of sections has been determined, the linker recursively marks as used any section referenced by their relocations. See --entry and --undefined. This option can be set when doing a partial link (enabled with option -r). In this case the root of symbols kept must be explicitely specified either by an --entry or --undefined option or by a "ENTRY" command in the linker script. --print-gc-sections --no-print-gc-sections List all sections removed by garbage collection. The listing is printed on stderr. This option is only effective if garbage collection has been enabled via the --gc-sections) option. The default behaviour (of not listing the sections that are removed) can be restored by specifying --no-print-gc-sections on the command line. --help Print a summary of the command-line options on the standard output and exit. --target-help Print a summary of all target specific options on the standard output and exit. -Map=mapfile Print a link map to the file mapfile. See the description of the -M option, above. --no-keep-memory ld normally optimizes for speed over memory usage by caching the symbol tables of input files in memory. This option tells ld to instead optimize for memory usage, by rereading the symbol tables as necessary. This may be required if ld runs out of memory space while linking a large executable. --no-undefined -z defs Report unresolved symbol references from regular object files. This is done even if the linker is creating a non-symbolic shared library. The switch --[no-]allow-shlib-undefined controls the behaviour for reporting unresolved references found in shared libraries being linked in. --allow-multiple-definition -z muldefs Normally when a symbol is defined multiple times, the linker will report a fatal error. These options allow multiple definitions and the first definition will be used. --allow-shlib-undefined --no-allow-shlib-undefined Allows or disallows undefined symbols in shared libraries. This switch is similar to --no-undefined except that it determines the behaviour when the undefined symbols are in a shared library rather than a regular object file. It does not affect how undefined symbols in regular object files are handled. The default behaviour is to report errors for any undefined symbols referenced in shared libraries if the linker is being used to create an executable, but to allow them if the linker is being used to create a shared library. The reasons for allowing undefined symbol references in shared libraries specified at link time are that: · A shared library specified at link time may not be the same as the one that is available at load time, so the symbol might actually be resolvable at load time. · There are some operating systems, eg BeOS and HPPA, where undefined symbols in shared libraries are normal. The BeOS kernel for example patches shared libraries at load time to select whichever function is most appropriate for the current architecture. This is used, for example, to dynamically select an appropriate memset function. --no-undefined-version Normally when a symbol has an undefined version, the linker will ignore it. This option disallows symbols with undefined version and a fatal error will be issued instead. --default-symver Create and use a default symbol version (the soname) for unversioned exported symbols. --default-imported-symver Create and use a default symbol version (the soname) for unversioned imported symbols. --no-warn-mismatch Normally ld will give an error if you try to link together input files that are mismatched for some reason, perhaps because they have been compiled for different processors or for different endiannesses. This option tells ld that it should silently permit such possible errors. This option should only be used with care, in cases when you have taken some special action that ensures that the linker errors are inappropriate. --no-warn-search-mismatch Normally ld will give a warning if it finds an incompatible library during a library search. This option silences the warning. --no-whole-archive Turn off the effect of the --whole-archive option for subsequent archive files. --noinhibit-exec Retain the executable output file whenever it is still usable. Normally, the linker will not produce an output file if it encounters errors during the link process; it exits without writing an output file when it issues any error whatsoever. -nostdlib Only search library directories explicitly specified on the command line. Library directories specified in linker scripts (including linker scripts specified on the command line) are ignored. --oformat=output-format ld may be configured to support more than one kind of object file. If your ld is configured this way, you can use the --oformat option to specify the binary format for the output object file. Even when ld is configured to support alternative object formats, you don’t usually need to specify this, as ld should be configured to produce as a default output format the most usual format on each machine. output-format is a text string, the name of a particular format supported by the BFD libraries. (You can list the available binary formats with objdump -i.) The script command "OUTPUT_FORMAT" can also specify the output format, but this option overrides it. -pie --pic-executable Create a position independent executable. This is currently only supported on ELF platforms. Position independent executables are similar to shared libraries in that they are relocated by the dynamic linker to the virtual address the OS chooses for them (which can vary between invocations). Like normal dynamically linked executables they can be executed and symbols defined in the executable cannot be overridden by shared libraries. -qmagic This option is ignored for Linux compatibility. -Qy This option is ignored for SVR4 compatibility. --relax An option with machine dependent effects. This option is only supported on a few targets. On some platforms, the --relax option performs global optimizations that become possible when the linker resolves addressing in the program, such as relaxing address modes and synthesizing new instructions in the output object file. On some platforms these link time global optimizations may make symbolic debugging of the resulting executable impossible. This is known to be the case for the Matsushita MN10200 and MN10300 family of processors. On platforms where this is not supported, --relax is accepted, but ignored. --retain-symbols-file=filename Retain only the symbols listed in the file filename, discarding all others. filename is simply a flat file, with one symbol name per line. This option is especially useful in environments (such as VxWorks) where a large global symbol table is accumulated gradually, to conserve run-time memory. --retain-symbols-file does not discard undefined symbols, or symbols needed for relocations. You may only specify --retain-symbols-file once in the command line. It overrides -s and -S. -rpath=dir Add a directory to the runtime library search path. This is used when linking an ELF executable with shared objects. All -rpath arguments are concatenated and passed to the runtime linker, which uses them to locate shared objects at runtime. The -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 -rpath-link option. If -rpath is not used when linking an ELF executable, the contents of the environment variable "LD_RUN_PATH" will be used if it is defined. The -rpath option may also be used on SunOS. By default, on SunOS, the linker will form a runtime search patch out of all the -L options it is given. If a -rpath option is used, the runtime search path will be formed exclusively using the -rpath options, ignoring the -L options. This can be useful when using gcc, which adds many -L options which may be on NFS mounted file systems. For compatibility with other ELF linkers, if the -R option is followed by a directory name, rather than a file name, it is treated as the -rpath option. -rpath-link=dir When using ELF or SunOS, one shared library may require another. This happens when an "ld -shared" link includes a shared library as one of the input files. When the linker encounters such a dependency when doing a non- shared, non-relocatable link, it will automatically try to locate the required shared library and include it in the link, if it is not included explicitly. In such a case, the -rpath-link option specifies the first set of directories to search. The -rpath-link option may specify a sequence of directory names either by specifying a list of names separated by colons, or by appearing multiple times. This option should be used with caution as it overrides the search path that may have been hard compiled into a shared library. In such a case it is possible to use unintentionally a different search path than the runtime linker would do. The linker uses the following search paths to locate required shared libraries: 1. Any directories specified by -rpath-link options. 2. Any directories specified by -rpath options. The difference between -rpath and -rpath-link is that directories specified by -rpath options are included in the executable and used at runtime, whereas the -rpath-link option is only effective at link time. Searching -rpath in this way is only supported by native linkers and cross linkers which have been configured with the --with-sysroot option. 3. On an ELF system, for native linkers, if the -rpath and -rpath-link options were not used, search the contents of the environment variable "LD_RUN_PATH". 4. On SunOS, if the -rpath option was not used, search any directories specified using -L options. 5. For a native linker, the search the contents of the environment variable "LD_LIBRARY_PATH". 6. For a native ELF linker, the directories in "DT_RUNPATH" or "DT_RPATH" of a shared library are searched for shared libraries needed by it. The "DT_RPATH" entries are ignored if "DT_RUNPATH" entries exist. 7. The default directories, normally /lib and /usr/lib. 8. For a native linker on an ELF system, if the file /etc/ld.so.conf exists, the list of directories found in that file. If the required shared library is not found, the linker will issue a warning and continue with the link. -shared -Bshareable Create a shared library. This is currently only supported on ELF, XCOFF and SunOS platforms. On SunOS, the linker will automatically create a shared library if the -e option is not used and there are undefined symbols in the link. --sort-common --sort-common=ascending --sort-common=descending This option tells ld to sort the common symbols by alignment in ascending or descending order when it places them in the appropriate output sections. The symbol alignments considered are sixteen-byte or larger, eight-byte, four-byte, two-byte, and one- byte. This is to prevent gaps between symbols due to alignment constraints. If no sorting order is specified, then descending order is assumed. --sort-section=name This option will apply "SORT_BY_NAME" to all wildcard section patterns in the linker script. --sort-section=alignment This option will apply "SORT_BY_ALIGNMENT" to all wildcard section patterns in the linker script. --split-by-file[=size] Similar to --split-by-reloc but creates a new output section for each input file when size is reached. size defaults to a size of 1 if not given. --split-by-reloc[=count] Tries to creates extra sections in the output file so that no single output section in the file contains more than count relocations. This is useful when generating huge relocatable files for downloading into certain real time kernels with the COFF object file format; since COFF cannot represent more than 65535 relocations in a single section. Note that this will fail to work with object file formats which do not support arbitrary sections. The linker will not split up individual input sections for redistribution, so if a single input section contains more than count relocations one output section will contain that many relocations. count defaults to a value of 32768. --stats Compute and display statistics about the operation of the linker, such as execution time and memory usage. --sysroot=directory Use directory as the location of the sysroot, overriding the configure-time default. This option is only supported by linkers that were configured using --with-sysroot. --traditional-format For some targets, the output of ld is different in some ways from the output of some existing linker. This switch requests ld to use the traditional format instead. For example, on SunOS, ld combines duplicate entries in the symbol string table. This can reduce the size of an output file with full debugging information by over 30 percent. Unfortunately, the SunOS "dbx" program can not read the resulting program ("gdb" has no trouble). The --traditional-format switch tells ld to not combine duplicate entries. --section-start=sectionname=org Locate a section in the output file at the absolute address given by org. You may use this option as many times as necessary to locate multiple sections in the command line. org must be a single hexadecimal integer; for compatibility with other linkers, you may omit the leading 0x usually associated with hexadecimal values. Note: there should be no white space between sectionname, the equals sign ("="), and org. -Tbss=org -Tdata=org -Ttext=org Same as --section-start, with ".bss", ".data" or ".text" as the sectionname. -Ttext-segment=org When creating an ELF executable or shared object, it will set the address of the first byte of the text segment. --unresolved-symbols=method Determine how to handle unresolved symbols. There are four possible values for method: ignore-all Do not report any unresolved symbols. report-all Report all unresolved symbols. This is the default. ignore-in-object-files Report unresolved symbols that are contained in shared libraries, but ignore them if they come from regular object files. ignore-in-shared-libs Report unresolved symbols that come from regular object files, but ignore them if they come from shared libraries. This can be useful when creating a dynamic binary and it is known that all the shared libraries that it should be referencing are included on the linker’s command line. The behaviour for shared libraries on their own can also be controlled by the --[no-]allow-shlib-undefined option. Normally the linker will generate an error message for each reported unresolved symbol but the option --warn-unresolved-symbols can change this to a warning. --dll-verbose --verbose Display the version number for ld and list the linker emulations supported. Display which input files can and cannot be opened. Display the linker script being used by the linker. --version-script=version-scriptfile Specify the name of a version script to the linker. This is typically used when creating shared libraries to specify additional information about the version hierarchy for the library being created. This option is only fully supported on ELF platforms which support shared libraries; see VERSION. It is partially supported on PE platforms, which can use version scripts to filter symbol visibility in auto-export mode: any symbols marked local in the version script will not be exported. --warn-common Warn when a common symbol is combined with another common symbol or with a symbol definition. Unix linkers allow this somewhat sloppy practise, but linkers on some other operating systems do not. This option allows you to find potential problems from combining global symbols. Unfortunately, some C libraries use this practise, so you may get some warnings about symbols in the libraries as well as in your programs. There are three kinds of global symbols, illustrated here by C examples: int i = 1; A definition, which goes in the initialized data section of the output file. extern int i; An undefined reference, which does not allocate space. There must be either a definition or a common symbol for the variable somewhere. int i; A common symbol. If there are only (one or more) common symbols for a variable, it goes in the uninitialized data area of the output file. The linker merges multiple common symbols for the same variable into a single symbol. If they are of different sizes, it picks the largest size. The linker turns a common symbol into a declaration, if there is a definition of the same variable. The --warn-common option can produce five kinds of warnings. Each warning consists of a pair of lines: the first describes the symbol just encountered, and the second describes the previous symbol encountered with the same name. One or both of the two symbols will be a common symbol. 1. Turning a common symbol into a reference, because there is already a definition for the symbol. (

): warning: common of `' overridden by definition (

): warning: defined here 2. Turning a common symbol into a reference, because a later definition for the symbol is encountered. This is the same as the previous case, except that the symbols are encountered in a different order. (

): warning: definition of `' overriding common (

): warning: common is here 3. Merging a common symbol with a previous same-sized common symbol. (

): warning: multiple common of `' (

): warning: previous common is here 4. Merging a common symbol with a previous larger common symbol. (

): warning: common of `' overridden by larger common (

): warning: larger common is here 5. Merging a common symbol with a previous smaller common symbol. This is the same as the previous case, except that the symbols are encountered in a different order. (

): warning: common of `' overriding smaller common (

): warning: smaller common is here --warn-constructors Warn if any global constructors are used. This is only useful for a few object file formats. For formats like COFF or ELF, the linker can not detect the use of global constructors. --warn-multiple-gp Warn if multiple global pointer values are required in the output file. This is only meaningful for certain processors, such as the Alpha. Specifically, some processors put large-valued constants in a special section. A special register (the global pointer) points into the middle of this section, so that constants can be loaded efficiently via a base-register relative addressing mode. Since the offset in base-register relative mode is fixed and relatively small (e.g., 16 bits), this limits the maximum size of the constant pool. Thus, in large programs, it is often necessary to use multiple global pointer values in order to be able to address all possible constants. This option causes a warning to be issued whenever this case occurs. --warn-once Only warn once for each undefined symbol, rather than once per module which refers to it. --warn-section-align Warn if the address of an output section is changed because of alignment. Typically, the alignment will be set by an input section. The address will only be changed if it not explicitly specified; that is, if the "SECTIONS" command does not specify a start address for the section. --warn-shared-textrel Warn if the linker adds a DT_TEXTREL to a shared object. --warn-alternate-em Warn if an object has alternate ELF machine code. --warn-unresolved-symbols If the linker is going to report an unresolved symbol (see the option --unresolved-symbols) it will normally generate an error. This option makes it generate a warning instead. --error-unresolved-symbols This restores the linker’s default behaviour of generating errors when it is reporting unresolved symbols. --whole-archive For each archive mentioned on the command line after the --whole-archive option, include every object file in the archive in the link, rather than searching the archive for the required object files. This is normally used to turn an archive file into a shared library, forcing every object to be included in the resulting shared library. This option may be used more than once. Two notes when using this option from gcc: First, gcc doesn’t know about this option, so you have to use -Wl,-whole-archive. Second, don’t forget to use -Wl,-no-whole-archive after your list of archives, because gcc will add its own list of archives to your link and you may not want this flag to affect those as well. --wrap=symbol Use a wrapper function for symbol. Any undefined reference to symbol will be resolved to "__wrap_symbol". Any undefined reference to "__real_symbol" will be resolved to symbol. This can be used to provide a wrapper for a system function. The wrapper function should be called "__wrap_symbol". If it wishes to call the system function, it should call "__real_symbol". Here is a trivial example: void * __wrap_malloc (size_t c) { printf ("malloc called with %zu\n", c); return __real_malloc (c); } If you link other code with this file using --wrap malloc, then all calls to "malloc" will call the function "__wrap_malloc" instead. The call to "__real_malloc" in "__wrap_malloc" will call the real "malloc" function. You may wish to provide a "__real_malloc" function as well, so that links without the --wrap option will succeed. If you do this, you should not put the definition of "__real_malloc" in the same file as "__wrap_malloc"; if you do, the assembler may resolve the call before the linker has a chance to wrap it to "malloc". --eh-frame-hdr Request creation of ".eh_frame_hdr" section and ELF "PT_GNU_EH_FRAME" segment header. --enable-new-dtags --disable-new-dtags This linker can create the new dynamic tags in ELF. But the older ELF systems may not understand them. If you specify --enable-new-dtags, the dynamic tags will be created as needed. If you specify --disable-new-dtags, no new dynamic tags will be created. By default, the new dynamic tags are not created. Note that those options are only available for ELF systems. --hash-size=number Set the default size of the linker’s hash tables to a prime number close to number. Increasing this value can reduce the length of time it takes the linker to perform its tasks, at the expense of increasing the linker’s memory requirements. Similarly reducing this value can reduce the memory requirements at the expense of speed. --hash-style=style Set the type of linker’s hash table(s). style can be either "sysv" for classic ELF ".hash" section, "gnu" for new style GNU ".gnu.hash" section or "both" for both the classic ELF ".hash" and new style GNU ".gnu.hash" hash tables. The default is "sysv". --reduce-memory-overheads This option reduces memory requirements at ld runtime, at the expense of linking speed. This was introduced to select the old O(n^2) algorithm for link map file generation, rather than the new O(n) algorithm which uses about 40% more memory for symbol storage. Another effect of the switch is to set the default hash table size to 1021, which again saves memory at the cost of lengthening the linker’s run time. This is not done however if the --hash-size switch has been used. The --reduce-memory-overheads switch may be also be used to enable other tradeoffs in future versions of the linker. --build-id --build-id=style Request creation of ".note.gnu.build-id" ELF note section. The contents of the note are unique bits identifying this linked file. style can be "uuid" to use 128 random bits, "sha1" to use a 160-bit SHA1 hash on the normative parts of the output contents, "md5" to use a 128-bit MD5 hash on the normative parts of the output contents, or "0xhexstring" to use a chosen bit string specified as an even number of hexadecimal digits ("-" and ":" characters between digit pairs are ignored). If style is omitted, "sha1" is used. The "md5" and "sha1" styles produces an identifier that is always the same in an identical output file, but will be unique among all nonidentical output files. It is not intended to be compared as a checksum for the file’s contents. A linked file may be changed later by other tools, but the build ID bit string identifying the original linked file does not change. Passing "none" for style disables the setting from any "--build-id" options earlier on the command line. The i386 PE linker supports the -shared option, which causes the output to be a dynamically linked library (DLL) instead of a normal executable. You should name the output "*.dll" when you use this option. In addition, the linker fully supports the standard "*.def" files, which may be specified on the linker command line like an object file (in fact, it should precede archives it exports symbols from, to ensure that they get linked in, just like a normal object file). In addition to the options common to all targets, the i386 PE linker support additional command line options that are specific to the i386 PE target. Options that take values may be separated from their values by either a space or an equals sign. --add-stdcall-alias If given, symbols with a stdcall suffix (@nn) will be exported as- is and also with the suffix stripped. [This option is specific to the i386 PE targeted port of the linker] --base-file file Use file as the name of a file in which to save the base addresses of all the relocations needed for generating DLLs with dlltool. [This is an i386 PE specific option] --dll Create a DLL instead of a regular executable. You may also use -shared or specify a "LIBRARY" in a given ".def" file. [This option is specific to the i386 PE targeted port of the linker] --enable-long-section-names --disable-long-section-names 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 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 generated with these long section names are slightly non-standard, carrying as they do a string table, and may generate confusing output when examined with non-GNU PE-aware tools, such as file viewers and dumpers. However, GDB relies on the use of PE long section names to find Dwarf-2 debug information sections in an executable image at runtime, and so if neither option is specified on the command- line, ld will enable long section names, overriding the default and technically correct behaviour, when it finds the presence of debug information while linking an executable image and not stripping symbols. [This option is valid for all PE targeted ports of the linker] --enable-stdcall-fixup --disable-stdcall-fixup If the link finds a symbol that it cannot resolve, it will attempt to do "fuzzy linking" by looking for another defined symbol that differs only in the format of the symbol name (cdecl vs stdcall) and will resolve that symbol by linking to the match. For example, the undefined symbol "_foo" might be linked to the function "_foo@12", or the undefined symbol "_bar@16" might be linked to the function "_bar". When the linker does this, it prints a warning, since it normally should have failed to link, but sometimes import libraries generated from third-party dlls may need this feature to be usable. If you specify --enable-stdcall-fixup, this feature is fully enabled and warnings are not printed. If you specify --disable-stdcall-fixup, this feature is disabled and such mismatches are considered to be errors. [This option is specific to the i386 PE targeted port of the linker] --export-all-symbols If given, all global symbols in the objects used to build a DLL will be exported by the DLL. Note that this is the default if there otherwise wouldn’t be any exported symbols. When symbols are explicitly exported via DEF files or implicitly exported via function attributes, the default is to not export anything else unless this option is given. Note that the symbols "DllMain@12", "DllEntryPoint@0", "DllMainCRTStartup@12", and "impure_ptr" will not be automatically exported. Also, symbols imported from other DLLs will not be re-exported, nor will symbols specifying the DLL’s internal layout such as those beginning with "_head_" or ending with "_iname". In addition, no symbols from "libgcc", "libstd++", "libmingw32", or "crtX.o" will be exported. Symbols whose names begin with "__rtti_" or "__builtin_" will not be exported, to help with C++ DLLs. Finally, there is an extensive list of cygwin- private symbols that are not exported (obviously, this applies on when building DLLs for cygwin targets). These cygwin-excludes are: "_cygwin_dll_entry@12", "_cygwin_crt0_common@8", "_cygwin_noncygwin_dll_entry@12", "_fmode", "_impure_ptr", "cygwin_attach_dll", "cygwin_premain0", "cygwin_premain1", "cygwin_premain2", "cygwin_premain3", and "environ". [This option is specific to the i386 PE targeted port of the linker] --exclude-symbols symbol,symbol,... Specifies a list of symbols which should not be automatically exported. The symbol names may be delimited by commas or colons. [This option is specific to the i386 PE targeted port of the linker] --file-alignment Specify the file alignment. Sections in the file will always begin at file offsets which are multiples of this number. This defaults to 512. [This option is specific to the i386 PE targeted port of the linker] --heap reserve --heap reserve,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 committed. [This option is specific to the i386 PE targeted port of the linker] --image-base value Use value as the base address of your program or dll. This is the lowest memory location that will be used when your program or dll is loaded. To reduce the need to relocate and improve performance of your dlls, each should have a unique base address and not overlap any other dlls. The default is 0x400000 for executables, and 0x10000000 for dlls. [This option is specific to the i386 PE targeted port of the linker] --kill-at If given, the stdcall suffixes (@nn) will be stripped from symbols before they are exported. [This option is specific to the i386 PE targeted port of the linker] --large-address-aware If given, the appropriate bit in the "Characteristics" field of the COFF header is set to indicate that this executable supports virtual addresses greater than 2 gigabytes. This should be used in conjunction with the /3GB or /USERVA=value megabytes switch in the "[operating systems]" section of the BOOT.INI. Otherwise, this bit has no effect. [This option is specific to PE targeted ports of the linker] --major-image-version 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] --major-os-version value Sets the major number of the "os version". Defaults to 4. [This option is specific to the i386 PE targeted port of the linker] --major-subsystem-version value Sets the major number of the "subsystem version". Defaults to 4. [This option is specific to the i386 PE targeted port of the linker] --minor-image-version value Sets the minor number of the "image version". Defaults to 0. [This option is specific to the i386 PE targeted port of the linker] --minor-os-version value Sets the minor number of the "os version". Defaults to 0. [This option is specific to the i386 PE targeted port of the linker] --minor-subsystem-version value Sets the minor number of the "subsystem version". Defaults to 0. [This option is specific to the i386 PE targeted port of the linker] --output-def file The linker will create the file file which will contain a DEF file corresponding to the DLL the linker is generating. This DEF file (which should be called "*.def") may be used to create an import library with "dlltool" or may be used as a reference to automatically or implicitly exported symbols. [This option is specific to the i386 PE targeted port of the linker] --out-implib file The linker will create the file file which will contain an import lib corresponding to the DLL the linker is generating. This import lib (which should be called "*.dll.a" or "*.a" may be used to link clients against the generated DLL; this behaviour makes it possible to skip a separate "dlltool" import library creation step. [This option is specific to the i386 PE targeted port of the linker] --enable-auto-image-base Automatically choose the image base for DLLs, unless one is specified using the "--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] --disable-auto-image-base Do not automatically generate a unique image base. If there is no user-specified image base ("--image-base") then use the platform default. [This option is specific to the i386 PE targeted port of the linker] --dll-search-prefix string When linking dynamically to a dll without an import library, search for ".dll" in preference to "lib.dll". This behaviour allows easy distinction between DLLs built for the various "subplatforms": native, cygwin, uwin, pw, etc. For instance, cygwin DLLs typically use "--dll-search-prefix=cyg". [This option is specific to the i386 PE targeted port of the linker] --enable-auto-import Do sophisticated linking of "_symbol" to "__imp__symbol" for DATA imports from DLLs, and create the necessary thunking symbols when building the import libraries with those DATA exports. Note: Use of the ’auto-import’ extension will cause the text section of the image file to be made writable. This does not conform to the PE- COFF format specification published by Microsoft. Note - use of the ’auto-import’ extension will also cause read only data which would normally be placed into the .rdata section to be placed into the .data section instead. This is in order to work around a problem with consts that is described here: http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html Using ’auto-import’ generally will ’just work’ -- but sometimes you may see this message: "variable ’’ can’t be auto-imported. Please read the documentation for ld’s "--enable-auto-import" for details." This message occurs when some (sub)expression accesses an address ultimately given by the sum of two constants (Win32 import tables only allow one). Instances where this may occur include accesses to member fields of struct variables imported from a DLL, as well as using a constant index into an array variable imported from a DLL. Any multiword variable (arrays, structs, long long, etc) may trigger this error condition. However, regardless of the exact data type of the offending exported variable, ld will always detect it, issue the warning, and exit. There are several ways to address this difficulty, regardless of the data type of the exported variable: One way is to use --enable-runtime-pseudo-reloc switch. This leaves the task of adjusting references in your client code for runtime environment, so this method works only when runtime environment supports this feature. A second solution is to force one of the ’constants’ to be a variable -- that is, unknown and un-optimizable at compile time. For arrays, there are two possibilities: a) make the indexee (the array’s address) a variable, or b) make the ’constant’ index a variable. Thus: extern type extern_array[]; extern_array[1] --> { volatile type *t=extern_array; t[1] } or extern type extern_array[]; extern_array[1] --> { volatile int t=1; extern_array[t] } For structs (and most other multiword data types) the only option is to make the struct itself (or the long long, or the ...) variable: extern struct s extern_struct; extern_struct.field --> { volatile struct s *t=&extern_struct; t->field } or extern long long extern_ll; extern_ll --> { volatile long long * local_ll=&extern_ll; *local_ll } A third method of dealing with this difficulty is to abandon ’auto-import’ for the offending symbol and mark it with "__declspec(dllimport)". However, in practise that requires using compile-time #defines to indicate whether you are building a DLL, building client code that will link to the DLL, or merely building/linking to a static library. In making the choice between the various methods of resolving the ’direct address with constant offset’ problem, you should consider typical real-world usage: Original: --foo.h extern int arr[]; --foo.c #include "foo.h" void main(int argc, char **argv){ printf("%d\n",arr[1]); } Solution 1: --foo.h extern int arr[]; --foo.c #include "foo.h" void main(int argc, char **argv){ /* This workaround is for win32 and cygwin; do not "optimize" */ volatile int *parr = arr; printf("%d\n",parr[1]); } Solution 2: --foo.h /* Note: auto-export is assumed (no __declspec(dllexport)) */ #if (defined(_WIN32) || defined(__CYGWIN__)) && \ !(defined(FOO_BUILD_DLL) || defined(FOO_STATIC)) #define FOO_IMPORT __declspec(dllimport) #else #define FOO_IMPORT #endif extern FOO_IMPORT int arr[]; --foo.c #include "foo.h" void main(int argc, char **argv){ printf("%d\n",arr[1]); } A fourth way to avoid this problem is to re-code your library to use a functional interface rather than a data interface for the offending variables (e.g. set_foo() and get_foo() accessor functions). [This option is specific to the i386 PE targeted port of the linker] --disable-auto-import Do not attempt to do sophisticated linking of "_symbol" to "__imp__symbol" for DATA imports from DLLs. [This option is specific to the i386 PE targeted port of the linker] --enable-runtime-pseudo-reloc If your code contains expressions described in --enable-auto-import section, that is, DATA imports from DLL with non-zero offset, this switch will create a vector of ’runtime pseudo relocations’ which can be used by runtime environment to adjust references to such data in your client code. [This option is specific to the i386 PE targeted port of the linker] --disable-runtime-pseudo-reloc Do not create pseudo relocations for non-zero offset DATA imports from DLLs. This is the default. [This option is specific to the i386 PE targeted port of the linker] --enable-extra-pe-debug Show additional debug info related to auto-import symbol thunking. [This option is specific to the i386 PE targeted port of the linker] --section-alignment Sets the section alignment. Sections in memory will always begin at addresses which are a multiple of this number. Defaults to 0x1000. [This option is specific to the i386 PE targeted port of the linker] --stack reserve --stack reserve,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 committed. [This option is specific to the i386 PE targeted port of the linker] --subsystem which --subsystem which:major --subsystem which:major.minor Specifies the subsystem under which your program will execute. The legal values for which are "native", "windows", "console", "posix", and "xbox". You may optionally set the subsystem version also. Numeric values are also accepted for which. [This option is specific to the i386 PE targeted port of the linker] The following options set flags in the "DllCharacteristics" field of the PE file header: [These options are specific to PE targeted ports of the linker] --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. --forceinteg Code integrity checks are enforced. --nxcompat The image is compatible with the Data Execution Prevention. This feature was introduced with MS Windows XP SP2 for i386 PE targets. --no-isolation Although the image understands isolation, do not isolate the image. --no-seh The image does not use SEH. No SE handler may be called from this image. --no-bind Do not bind this image. --wdmdriver The driver uses the MS Windows Driver Model. --tsaware The image is Terminal Server aware. The 68HC11 and 68HC12 linkers support specific options to control the memory bank switching mapping and trampoline code generation. --no-trampoline This option disables the generation of trampoline. By default a trampoline is generated for each far function which is called using a "jsr" instruction (this happens when a pointer to a far function is taken). --bank-window name This option indicates to the linker the name of the memory region in the MEMORY specification that describes the memory bank window. The definition of such region is then used by the linker to compute paging and addresses within the memory window. The following options are supported to control handling of GOT generation when linking for 68K targets. --got=type This option tells the linker which GOT generation scheme to use. type should be one of single, negative, multigot or target. For more information refer to the Info entry for ld. ENVIRONMENT You can change the behaviour of ld with the environment variables "GNUTARGET", "LDEMULATION" and "COLLECT_NO_DEMANGLE". "GNUTARGET" determines the input-file object format if you don’t use -b (or its synonym --format). Its value should be one of the BFD names for an input format. If there is no "GNUTARGET" in the environment, ld uses the natural format of the target. If "GNUTARGET" is set to "default" then BFD attempts to discover the input format by examining binary input files; this method often succeeds, but there are potential ambiguities, since there is no method of ensuring that the magic number used to specify object-file formats is unique. However, the configuration procedure for BFD on each system places the conventional format for that system first in the search-list, so ambiguities are resolved in favor of convention. "LDEMULATION" determines the default emulation if you don’t use the -m option. The emulation can affect various aspects of linker behaviour, particularly the default linker script. You can list the available emulations with the --verbose or -V options. If the -m option is not used, and the "LDEMULATION" environment variable is not defined, the default emulation depends upon how the linker was configured. Normally, the linker will default to demangling symbols. However, if "COLLECT_NO_DEMANGLE" is set in the environment, then it will default to not demangling symbols. This environment variable is used in a similar fashion by the "gcc" linker wrapper program. The default may be overridden by the --demangle and --no-demangle options. SEE ALSO ar(1), nm(1), objcopy(1), objdump(1), readelf(1) and the Info entries for binutils and ld. COPYRIGHT Copyright (c) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 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 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License". binutils-2.20.51.0.2 2019-02-26 LD(1)

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