ぷるぷるの雑記

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GCCでリンクしているライブラリを知りたい

GCCはオプションなしでビルド工程を自動で行ってくれますが、だからこそデフォルトでリンクされているライブラリが分かりにくいです.

デフォルトでリンクされるライブラリやリンカスクリプトを知りたい場合は、 -Wl,--verbose オプションをつけてリンカに--verboseオプションを渡してやるとよいです.

そうするとリンカがディレクトリを巡回し、 最初に見つかったライブラリを採用するさま が見て取れます.

以下はWindowsでMinGWを用いてビルドしたときのログです. 以下の順番で ライブラリとスタートアップファイル をリンクしていることが分かります.

  1. リンクする順番に-lnameオプションをつけてldコマンドを呼び出す
  2. スタートアップファイルをリンクする
  3. GCC内部の環境変数にしたがってディレクトリを巡回し、ライブラリを検索する. 見つかるまで複数のフォルダを順番に巡回する
  4. ライブラリが見つかれば未解決なシンボルを含むモジュールをリンクする. しばらく3と4を繰り返す
  5. スタートアップファイルをリンクする
GNU ld (GNU Binutils) 2.30
  Supported emulations:
   i386pep
   i386pe
using internal linker script:
==================================================
/* Default linker script, for normal executables */
/* Copyright (C) 2014-2018 Free Software Foundation, Inc.
   Copying and distribution of this script, with or without modification,
   are permitted in any medium without royalty provided the copyright
   notice and this notice are preserved.  */
OUTPUT_FORMAT(pei-x86-64)
SEARCH_DIR("=/c/mingw810/prerequisites/x86_64-binutils-nomulti/x86_64-w64-mingw32/lib"); SEARCH_DIR("=/c/mingw810/prerequisites/x86_64-binutils-nomulti/lib"); SEARCH_DIR("=/usr/local/lib"); SEARCH_DIR("=/lib"); SEARCH_DIR("=/usr/lib");
SECTIONS
{
  /* Make the virtual address and file offset synced if the alignment is
     lower than the target page size. */
  . = SIZEOF_HEADERS;
  . = ALIGN(__section_alignment__);
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 省略 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  
}


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attempt to open C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/crt2.o succeeded
C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/crt2.o
attempt to open C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/crtbegin.o succeeded
C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/crtbegin.o
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 省略 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
attempt to open C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.dll.a failed
attempt to open C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/mingw32.dll.a failed
attempt to open C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a succeeded
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-gccmain.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-natstart.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-wildcard.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-charmax.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-dllargv.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-gs_support.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-_newmode.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-tlssup.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-cinitexe.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-merr.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-CRT_fp10.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-mingw_helpers.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-pseudo-reloc.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-xtxtmode.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-crt_handler.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-tlsthrd.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-tlsmcrt.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-pseudo-reloc-list.o
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmingw32.a)lib64_libmingw32_a-pesect.o
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 省略 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
attempt to open C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmsvcrt.dll.a failed
attempt to open C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/msvcrt.dll.a failed
attempt to open C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmsvcrt.a succeeded
(C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/../../../../x86_64-w64-mingw32/lib/../lib/libmsvcrt.a)duags00253.o
attempt to open C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/crtend.o succeeded
C:/Program Files/mingw-w64/x86_64-8.1.0-posix-seh-rt_v6-rev0/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/8.1.0/crtend.o