c++ - gcc undefined reference 即使 ld 找到库并且它包含所需的函数

Question

我从事许多项目，我必须为此交叉编译许多库，有些是内部的，有些不是。在为我们的一个系统开发交叉编译的应用程序时，我不得不为我的应用程序导入一些交叉编译的内部库。我正在为 Eclipse 中的应用程序使用 autotools。无论我是否在 Eclipse 中，问题都会发生。不管我编译的平台是什么，它都会发生，所以我的所有不同版本的 gcc 都会遇到相同的链接错误。当我编译应用程序时，各个模块 (*.c) 编译正常，但是当发出最终 gcc 命令将所有内容链接到最终程序时，我收到“对 GetCanMpdConfig 的 undefined reference ”错误。

现在，最重要的是:链接器实际上找到了文件(我已经用 -Wl,--verbose 验证了这一点，让 gcc 打印链接描述文件)。我将您的注意力特别引向有关 -lcanmpdconf 的行:

Making clean in src
make[1]: Entering directory `/home/amarshall3/workspace/can_mpd/src'
test -z "can_mpd" || rm -f can_mpd
rm -f *.o
make[1]: Leaving directory `/home/amarshall3/workspace/can_mpd/src'
make[1]: Entering directory `/home/amarshall3/workspace/can_mpd'
make[1]: Nothing to be done for `clean-am'.
make[1]: Leaving directory `/home/amarshall3/workspace/can_mpd'
Making all in src
make[1]: Entering directory `/home/amarshall3/workspace/can_mpd/src'
i686-linux-gnu-g++ -DPACKAGE_NAME=\"can_mpd\" -DPACKAGE_TARNAME=\"can_mpd\" -DPACKAGE_VERSION=\"1.13\" -DPACKAGE_STRING=\"can_mpd\ 1.13\" -DPACKAGE_BUGREPORT=\"\" -DPACKAGE_URL=\"\" -DPLATFORM=generic_x86 -I.    -DBUILDSTAMP="\"`date '+%F %T'`\"" -I../dependencies/canmpdconf/1.0/generic_x86/include -I../dependencies/mow2monitor/1.0/generic_x86/include -DGENERIC_X86   -g -ggdb -O0 -Wall -Wl,--verbose -MT can_mpd-can_mpd.o -MD -MP -MF .deps/can_mpd-can_mpd.Tpo -c -o can_mpd-can_mpd.o `test -f 'can_mpd.cpp' || echo './'`can_mpd.cpp
mv -f .deps/can_mpd-can_mpd.Tpo .deps/can_mpd-can_mpd.Po
i686-linux-gnu-g++ -DPACKAGE_NAME=\"can_mpd\" -DPACKAGE_TARNAME=\"can_mpd\" -DPACKAGE_VERSION=\"1.13\" -DPACKAGE_STRING=\"can_mpd\ 1.13\" -DPACKAGE_BUGREPORT=\"\" -DPACKAGE_URL=\"\" -DPLATFORM=generic_x86 -I.    -DBUILDSTAMP="\"`date '+%F %T'`\"" -I../dependencies/canmpdconf/1.0/generic_x86/include -I../dependencies/mow2monitor/1.0/generic_x86/include -DGENERIC_X86   -g -ggdb -O0 -Wall -Wl,--verbose -MT can_mpd-mpd_can.o -MD -MP -MF .deps/can_mpd-mpd_can.Tpo -c -o can_mpd-mpd_can.o `test -f 'mpd_can.cpp' || echo './'`mpd_can.cpp
mv -f .deps/can_mpd-mpd_can.Tpo .deps/can_mpd-mpd_can.Po
i686-linux-gnu-g++ -DPACKAGE_NAME=\"can_mpd\" -DPACKAGE_TARNAME=\"can_mpd\" -DPACKAGE_VERSION=\"1.13\" -DPACKAGE_STRING=\"can_mpd\ 1.13\" -DPACKAGE_BUGREPORT=\"\" -DPACKAGE_URL=\"\" -DPLATFORM=generic_x86 -I.    -DBUILDSTAMP="\"`date '+%F %T'`\"" -I../dependencies/canmpdconf/1.0/generic_x86/include -I../dependencies/mow2monitor/1.0/generic_x86/include -DGENERIC_X86   -g -ggdb -O0 -Wall -Wl,--verbose -MT can_mpd-mpd_multiplexing.o -MD -MP -MF .deps/can_mpd-mpd_multiplexing.Tpo -c -o can_mpd-mpd_multiplexing.o `test -f 'mpd_multiplexing.cpp' || echo './'`mpd_multiplexing.cpp
mv -f .deps/can_mpd-mpd_multiplexing.Tpo .deps/can_mpd-mpd_multiplexing.Po
i686-linux-gnu-g++ -DPACKAGE_NAME=\"can_mpd\" -DPACKAGE_TARNAME=\"can_mpd\" -DPACKAGE_VERSION=\"1.13\" -DPACKAGE_STRING=\"can_mpd\ 1.13\" -DPACKAGE_BUGREPORT=\"\" -DPACKAGE_URL=\"\" -DPLATFORM=generic_x86 -I.    -DBUILDSTAMP="\"`date '+%F %T'`\"" -I../dependencies/canmpdconf/1.0/generic_x86/include -I../dependencies/mow2monitor/1.0/generic_x86/include -DGENERIC_X86   -g -ggdb -O0 -Wall -Wl,--verbose -MT can_mpd-serial_can_provider.o -MD -MP -MF .deps/can_mpd-serial_can_provider.Tpo -c -o can_mpd-serial_can_provider.o `test -f 'provider/serial_can_provider.cpp' || echo './'`provider/serial_can_provider.cpp
mv -f .deps/can_mpd-serial_can_provider.Tpo .deps/can_mpd-serial_can_provider.Po
i686-linux-gnu-g++ -DPACKAGE_NAME=\"can_mpd\" -DPACKAGE_TARNAME=\"can_mpd\" -DPACKAGE_VERSION=\"1.13\" -DPACKAGE_STRING=\"can_mpd\ 1.13\" -DPACKAGE_BUGREPORT=\"\" -DPACKAGE_URL=\"\" -DPLATFORM=generic_x86 -I.    -DBUILDSTAMP="\"`date '+%F %T'`\"" -I../dependencies/canmpdconf/1.0/generic_x86/include -I../dependencies/mow2monitor/1.0/generic_x86/include -DGENERIC_X86   -g -ggdb -O0 -Wall -Wl,--verbose -MT can_mpd-komodo_can_provider.o -MD -MP -MF .deps/can_mpd-komodo_can_provider.Tpo -c -o can_mpd-komodo_can_provider.o `test -f 'provider/komodo_can_provider.cpp' || echo './'`provider/komodo_can_provider.cpp
mv -f .deps/can_mpd-komodo_can_provider.Tpo .deps/can_mpd-komodo_can_provider.Po
i686-linux-gnu-gcc -DPACKAGE_NAME=\"can_mpd\" -DPACKAGE_TARNAME=\"can_mpd\" -DPACKAGE_VERSION=\"1.13\" -DPACKAGE_STRING=\"can_mpd\ 1.13\" -DPACKAGE_BUGREPORT=\"\" -DPACKAGE_URL=\"\" -DPLATFORM=generic_x86 -I.     -g -O2 -MT komodo.o -MD -MP -MF .deps/komodo.Tpo -c -o komodo.o `test -f 'can/komodo/komodo.c' || echo './'`can/komodo/komodo.c
mv -f .deps/komodo.Tpo .deps/komodo.Po
i686-linux-gnu-g++ -DBUILDSTAMP="\"`date '+%F %T'`\"" -I../dependencies/canmpdconf/1.0/generic_x86/include -I../dependencies/mow2monitor/1.0/generic_x86/include -DGENERIC_X86   -g -ggdb -O0 -Wall -Wl,--verbose -L../dependencies/canmpdconf/1.0/generic_x86/lib -L../dependencies/mow2monitor/1.0/generic_x86/lib -Wl,--verbose -o can_mpd can_mpd-can_mpd.o can_mpd-mpd_can.o can_mpd-mpd_multiplexing.o can_mpd-serial_can_provider.o can_mpd-komodo_can_provider.o komodo.o   -lcanmpdconf -lmow2monitor -lpthread -ldl 
GNU ld (GNU Binutils for Ubuntu) 2.23.52.20130913
  Supported emulations:
   elf_i386
   i386linux
   elf32_x86_64
   elf_x86_64
   elf_l1om
   elf_k1om
   i386pep
   i386pe
GNU ld (GNU Binutils for Ubuntu) 2.23.52.20130913
  Supported emulations:
   elf_i386
   i386linux
   elf32_x86_64
   elf_x86_64
   elf_l1om
   elf_k1om
   i386pep
   i386pe
using internal linker script:
==================================================
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OUTPUT_FORMAT("elf32-i386", "elf32-i386",
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OUTPUT_ARCH(i386)
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SECTIONS
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==================================================
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/crt1.o succeeded
/usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/crt1.o
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/crti.o succeeded
/usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/crti.o
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/crtbegin.o succeeded
/usr/lib/gcc/i686-linux-gnu/4.8/crtbegin.o
attempt to open can_mpd-can_mpd.o succeeded
can_mpd-can_mpd.o
attempt to open can_mpd-mpd_can.o succeeded
can_mpd-mpd_can.o
attempt to open can_mpd-mpd_multiplexing.o succeeded
can_mpd-mpd_multiplexing.o
attempt to open can_mpd-serial_can_provider.o succeeded
can_mpd-serial_can_provider.o
attempt to open can_mpd-komodo_can_provider.o succeeded
can_mpd-komodo_can_provider.o
attempt to open komodo.o succeeded
komodo.o
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libcanmpdconf.so succeeded
-lcanmpdconf (../dependencies/canmpdconf/1.0/generic_x86/lib/libcanmpdconf.so)
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libmow2monitor.so failed
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libmow2monitor.a failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libmow2monitor.so succeeded
-lmow2monitor (../dependencies/mow2monitor/1.0/generic_x86/lib/libmow2monitor.so)
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libpthread.so failed
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libpthread.a failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libpthread.so failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libpthread.a failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libpthread.so failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libpthread.a failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/libpthread.so succeeded
opened script file /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/libpthread.so
opened script file /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/libpthread.so
attempt to open /lib/i386-linux-gnu/libpthread.so.0 succeeded
/lib/i386-linux-gnu/libpthread.so.0
attempt to open /usr/lib/i386-linux-gnu/libpthread_nonshared.a succeeded
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libdl.so failed
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libdl.a failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libdl.so failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libdl.a failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libdl.so failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libdl.a failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/libdl.so succeeded
-ldl (/usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/libdl.so)
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libstdc++.so failed
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libstdc++.a failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libstdc++.so failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libstdc++.a failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libstdc++.so succeeded
-lstdc++ (/usr/lib/gcc/i686-linux-gnu/4.8/libstdc++.so)
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libm.so failed
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libm.a failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libm.so failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libm.a failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libm.so failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libm.a failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/libm.so succeeded
-lm (/usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/libm.so)
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libgcc_s.so failed
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libgcc_s.a failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libgcc_s.so failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libgcc_s.a failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libgcc_s.so succeeded
-lgcc_s (/usr/lib/gcc/i686-linux-gnu/4.8/libgcc_s.so)
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libgcc.so failed
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libgcc.a failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libgcc.so failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libgcc.a failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libgcc.so failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libgcc.a succeeded
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libc.so failed
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libc.a failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libc.so failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libc.a failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libc.so failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libc.a failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/libc.so succeeded
opened script file /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/libc.so
opened script file /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/libc.so
attempt to open /lib/i386-linux-gnu/libc.so.6 succeeded
/lib/i386-linux-gnu/libc.so.6
attempt to open /usr/lib/i386-linux-gnu/libc_nonshared.a succeeded
(/usr/lib/i386-linux-gnu/libc_nonshared.a)elf-init.oS
(/usr/lib/i386-linux-gnu/libc_nonshared.a)atexit.oS
attempt to open /lib/i386-linux-gnu/ld-linux.so.2 succeeded
/lib/i386-linux-gnu/ld-linux.so.2
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libgcc_s.so failed
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libgcc_s.a failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libgcc_s.so failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libgcc_s.a failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libgcc_s.so succeeded
-lgcc_s (/usr/lib/gcc/i686-linux-gnu/4.8/libgcc_s.so)
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libgcc.so failed
attempt to open ../dependencies/canmpdconf/1.0/generic_x86/lib/libgcc.a failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libgcc.so failed
attempt to open ../dependencies/mow2monitor/1.0/generic_x86/lib/libgcc.a failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libgcc.so failed
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/libgcc.a succeeded
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/crtend.o succeeded
/usr/lib/gcc/i686-linux-gnu/4.8/crtend.o
attempt to open /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/crtn.o succeeded
/usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/crtn.o
ld-linux.so.2 needed by /lib/i386-linux-gnu/libpthread.so.0
found ld-linux.so.2 at /lib/i386-linux-gnu/ld-linux.so.2
libm.so.6 needed by /usr/lib/gcc/i686-linux-gnu/4.8/libstdc++.so
found libm.so at /usr/lib/gcc/i686-linux-gnu/4.8/../../../i386-linux-gnu/libm.so
make[1]: Leaving directory `/home/amarshall3/workspace/can_mpd/src'
can_mpd-can_mpd.o: In function `main':
/home/amarshall3/workspace/can_mpd/src/can_mpd.cpp:180: undefined reference to  `GetCanMpdConfig(CAN_MPD_CONFIG*, unsigned int*)'
collect2: error: ld returned 1 exit status
make[1]: *** [can_mpd] Error 1
make: *** [all-recursive] Error 1

我还验证了该库适用于正确的平台 (x86)，因此格式正确。我还验证了它确实包含所需的符号 (GetCanMpdConfig) 以及 nm 的输出:

0000305c B __bss_start
0000305c b completed.6608
         w __cxa_finalize@@GLIBC_2.1.3
00000940 t deregister_tm_clones
000009d0 t __do_global_dtors_aux
00002e88 t __do_global_dtors_aux_fini_array_entry
00003058 d __dso_handle
00002ee4 d _DYNAMIC
0000305c D _edata
00003060 B _end
         U __errno_location@@GLIBC_2.0
00002ea0 d Errors
         U fclose@@GLIBC_2.1
         U fgets@@GLIBC_2.0
00001184 T _fini
         U fopen@@GLIBC_2.1
         U __fprintf_chk@@GLIBC_2.3.4
00000a20 t frame_dummy
00002e84 t __frame_dummy_init_array_entry
000014e8 r __FRAME_END__
00000ef0 T GetCanMpdConfError
00000b60 T GetCanMpdConfig
00000a60 T GetCanMpdConfVersion
         U GetConfigFilePath
00003000 d _GLOBAL_OFFSET_TABLE_
         w __gmon_start__
00002ec0 d Handlers
000007c4 T _init
         w _ITM_deregisterTMCloneTable
         w _ITM_registerTMCloneTable
00002e8c d __JCR_END__
00002e8c d __JCR_LIST__
         w _Jv_RegisterClasses
00000f20 T read_provider_type
000010c0 T read_serial_baud
00001010 T read_serial_device
00000980 t register_tm_clones
00000a80 T SetCanMpdConfig
         U __stack_chk_fail@@GLIBC_2.4
00001170 t __stack_chk_fail_local
         U strchr@@GLIBC_2.0
         U strlen@@GLIBC_2.0
         U strncmp@@GLIBC_2.0
         U strncpy@@GLIBC_2.0
         U strtol@@GLIBC_2.0
0000305c d __TMC_END__
00000f90 T write_provider_type
00001110 T write_serial_baud
00001060 T write_serial_device
00000930 t __x86.get_pc_thunk.bx
00000f18 t __x86.get_pc_thunk.cx
         U __xstat@@GLIBC_2.0

总结一下:1) gcc 命令中的链接顺序是正确的(-llibname 在-o blah.cpp 之后)2)链接器找到库(libcanmpdconf.so)3) 库的格式适合平台 (x86)4) 库包含符号(见 nm 输出)

据我所知，应该没有理由对链接器可以找到的明确存在于我的库中的任何符号有一个 undefined reference 。有没有人知道我可以尝试解决此问题或可能有什么问题的任何其他方法？

Answer 1

你会不会遇到一个

extern "C" 

问题？