通过“未定义的引用 `boost::system::get_system_category()”链接到 boost barfs；

Question

我在静态链接使用 boost 1.35 库的应用程序时遇到问题。我使用的是 Linux debian Lenny box，带有 G++ 4.3.2。没有 -static 的链接可以顺利进行。

具体来说，

g++ -Wall -Wextra  -pedantic -ggdb3 -O0  -static -l boost_thread-mt -lboost_system-mt -lboost_program_options-mt -lssl -lpthread -l crypto  main.o comandos.o utils.o tunnel.o opciones.o decode.o sysutils.o -o sapp  

main.o: In function `__static_initialization_and_destruction_0':
/usr/include/boost/system/error_code.hpp:204:undefined reference to `boost::system::get_system_category()'
/usr/include/boost/system/error_code.hpp:205: undefined reference to `boost::system::get_posix_category()'
/usr/include/boost/system/error_code.hpp:209: undefined reference to `boost::system::get_posix_category()'
/usr/include/boost/system/error_code.hpp:210: undefined reference to `boost::system::get_system_category()'

我链接的是 boost_system-mt，它可以在我的盒子上的 /usr/lib 中找到。如果我链接到非多线程安全版本的 boost_system (-lboost_system)，也会发生同样的事情

sarraga@saggy:~/sapp/src$ ls -al /usr/lib/libboost_system*a
-rw-r--r-- 1 root root 23506 2008-05-23 05:32 /usr/lib/libboost_system.a
lrwxrwxrwx 1 root root    17 2010-08-26 19:10 /usr/lib/libboost_system-gcc42-1_35.a -> libboost_system.a
lrwxrwxrwx 1 root root    20 2010-08-26 19:10 /usr/lib/libboost_system-gcc42-mt-1_35.a -> libboost_system-mt.a
-rw-r--r-- 1 root root 23506 2008-05-23 05:32 /usr/lib/libboost_system-mt.a

并且我在那里找到了未解析的符号

sarraga@saggy:~/sapp/src$ nm -C /usr/lib/libboost_system-mt.a | grep 'T.*get.*category'
00000050 T boost::system::get_posix_category()
000000b0 T boost::system::get_system_category()

strace 显示链接器打开了库

 sarraga@saggy:~/sapp/src$ strace -f make 2>&1 | grep boost_system
[pid 15016] execve("/usr/bin/g++", ["g++", "-Wall", "-Wextra", "-pedantic", "-ggdb3", "-O0", "-static", "-l", "boost_thread-mt", "-lboost_system-mt", "-lboost_program_options-mt", "-lssl", "-lpthread", "-l", "crypto", "main.o", ...], [/* 41 vars */] <unfinished ...>
...
[pid 15018] open("/usr/lib/gcc/i486-linux-gnu/4.3.2/../../../../lib/libboost_system-mt.a", O_RDONLY|O_LARGEFILE) = 8

这是 debian 中 boost 的标准软件包安装，

sarraga@saggy:~/sapp/src$ dpkg -l | grep boos
ii  libboost-date-time1.35-dev           1.35.0-5                   set of date-time libraries based on generic programming
ii  libboost-date-time1.35.0             1.35.0-5                   set of date-time libraries based on generic programming
ii  libboost-filesystem1.35-dev          1.35.0-5                   filesystem operations (portable paths, iteration over d
ii  libboost-filesystem1.35.0            1.35.0-5                   filesystem operations (portable paths, iteration over d
ii  libboost-graph1.35-dev               1.35.0-5                   generic graph components and algorithms in C++
ii  libboost-graph1.35.0                 1.35.0-5                   generic graph components and algorithms in C++
ii  libboost-iostreams1.35-dev           1.35.0-5                   Boost.Iostreams Library development files
ii  libboost-iostreams1.35.0             1.35.0-5                   Boost.Iostreams Library
ii  libboost-program-options1.35-dev     1.35.0-5                   program options library for C++
ii  libboost-program-options1.35.0       1.35.0-5                   program options library for C++
ii  libboost-python1.35-dev              1.35.0-5                   Boost.Python Library development files
ii  libboost-python1.35.0                1.35.0-5                   Boost.Python Library
ii  libboost-regex1.35-dev               1.35.0-5                   regular expression library for C++
ii  libboost-regex1.35.0                 1.35.0-5                   regular expression library for C++
ii  libboost-serialization1.35-dev       1.35.0-5                   serialization library for C++
ii  libboost-serialization1.35.0         1.35.0-5                   serialization library for C++
ii  libboost-signals1.35-dev             1.35.0-5                   managed signals and slots library for C++
ii  libboost-signals1.35.0               1.35.0-5                   managed signals and slots library for C++
ii  libboost-system1.35-dev              1.35.0-5                   Operating system (e.g. diagnostics support) library
ii  libboost-system1.35.0                1.35.0-5                   Operating system (e.g. diagnostics support) library
ii  libboost-test1.35-dev                1.35.0-5                   components for writing and executing test suites
ii  libboost-test1.35.0                  1.35.0-5                   components for writing and executing test suites
ii  libboost-thread1.35-dev              1.35.0-5                   portable C++ multi-threading
ii  libboost-thread1.35.0                1.35.0-5                   portable C++ multi-threading
ii  libboost-wave1.35-dev                1.35.0-5                   C99/C++ preprocessor library
ii  libboost-wave1.35.0                  1.35.0-5                   C99/C++ preprocessor library
ii  libboost1.35-dev                     1.35.0-5                   Boost C++ Libraries development files
ii  libboost1.35-doc                     1.35.0-5                   Boost.org libraries documentation

我确信我错过了一个愚蠢的细节，但我找不到它。有人帮忙吗？

Answer 1

当静态链接时，链接器期望库位于包含对它们的引用的文件之后。您需要将 .o 文件移到 -l 标志之前。这个想法是，后面的文件“填充”早期文件中包含的引用——因为您的 .o 文件是最后的，链接器希望它们填充 boost_system 中任何缺失的符号，而不是反之亦然。当您动态链接时，顺序并不重要，因为直到第一次在运行时使用符号时它才会解析符号（那时它知道要在其中查找符号的库的完整列表）。