便利库中的符号不​​能以可执行文件导出

问题描述

我有一个程序， code>（有些谷歌搜索表明，这些是这个问题的常见原因。）

有人可以帮我理解这里发生了什么吗？

解决方案

我设法解决了这个问题。这是John Calcote出色的Autotools书籍的说明，它指出了我的正确方向：
$ b

抵消这种行为，可以使用 - whole-archive 标志来进行libtool。但是，这会导致所有系统库中的所有符号都被拉入，导致大量双符号定义错误。因此， - whole-archive 需要在链接器命令行上的 libconvenience.a 之前，它需要后面紧跟着 - no-whole-archive ，以便其他库不以那种方式处理。这有点困难，因为automake和libtool并不能真正保证你的标志在命令行上保持相同的顺序，但是 Makefile.am 中的这一行做到了这一点：

  myprogram_LDFLAGS = -Wl， -  export-dynamic \ 
 -Wl， -  whole-archive，libconvenience /libconvenience.a,-no-whole-archive 
  

I have a program, myprogram, which is linked with a static convenience library, call it libconvenience.a, which contains a function, func(). The function func() isn't called anywhere in myprogram; it needs to be able to be called from a plugin library, plugin.so.

The symbol func() is not getting exported dynamically in myprogram. If I run

nm myprogram | grep func

I get nothing. However, it isn't missing from libconvenience.a:

I am using automake, but if I do the last linking step by hand on the command line instead, it doesn't work either:

gcc -Wl,--export-dynamic -o myprogram *.o libconvenience/libconvenience.a `pkg-config --libs somelibraries`

However, if I link the program like this, skipping the use of a convenience library and linking the object files that would have gone into libconvenience.a directly, func() shows up in myprogram's symbols as it should:

gcc -Wl,--export-dynamic -o myprogram *.o libconvenience/*.o `pkg-config --libs somelibraries`

If I add a dummy call to func() somewhere in myprogram, then func() also shows up in myprogram's symbols. But I thought that --export-dynamic was supposed to export all symbols regardless of whether they were used in the program or not!

I am using automake 1.11.1 and gcc 4.5.1 on Fedora 14. I am also using Libtool 2.2.10 to build plugin.so (but not the convenience library.)

I didn't forget to put -Wl,--export-dynamic in myprogram_LDFLAGS, nor did I forget to put the source that contains func() in libconvenience_a_SOURCES (some Googling suggests that these are common causes of this problem.)

Can somebody help me understand what is going on here?

解决方案

I managed to solve it. It was this note from John Calcote's excellent Autotools book that pointed me in the right direction:

To counteract this behavior, one can use the --whole-archive flag to libtool. However, this causes all the symbols from all the system libraries to be pulled in also, causing lots of double symbol definition errors. So --whole-archive needs to be right before libconvenience.a on the linker command line, and it needs to be followed by --no-whole-archive so that the other libraries aren't treated that way. This is a bit difficult since automake and libtool don't really guarantee keeping your flags in the same order on the command line, but this line in Makefile.am did the trick:

myprogram_LDFLAGS = -Wl,--export-dynamic \
    -Wl,--whole-archive,libconvenience/libconvenience.a,--no-whole-archive

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