Question

I m 利用海合会从一组C++源文档中建立共同物体档案。所有关于建筑设计的示意图(.so的档案都显示在后编印的编号。例如:



gcc -shared -Wl,-soname,libmean.so.1 -o libmean.so.1.0.1  calc_mean.o


这将产生<代码>。

Additionally, if I browse the /usr/lib directory on my local machine, I see that many of the .so files have version numbers at the end.

However, when I compile a shared object file and place it in /usr/lib, the linker is unable to find it if I put a version number at the end.  If I remove the version number, it works fine.  I really don t care about putting a version number or not, I just don t understand why this seems to be a common convention, and yet this causes the shared library to not work with the linker.  So, what s going on here?  Why is there a convention to place the version number at the end of an .so file name?

Answer 1

The version number is appended so you can have multiple incompatible library versions coexisting in the system. You should increment the major version number (the number in soname) every time you change the API in an incompatible way (assuming the previous version is installed and used in the system, of course).

The 2nd and 3rd numbers in the file name allows for multiple minor revisions of the library in the system, switchable system-wide with a simple symlink update.

At link time you can give the .so file name as a linker argument, instead of -l option. ldd is smart enough to extract the soname from it, the binary linked this way uses it to find the library.

例如,请使用图书馆和双轨制进行编辑:

czajnik@czajnik:~/z$ gcc -shared -Wl,-soname,libtest.so.2 -o libtest.so.2.3.4  a.c 
czajnik@czajnik:~/z$ gcc -o test b.c -L. ./libtest.so.2.3.4

您可使用斜体来核实,双筒现在看上libtest.so.2:

czajnik@czajnik:~/z$ LD_LIBRARY_PATH=. ldd ./test
    linux-gate.so.1 =>  (0x002c1000)
    libtest.so.2 => not found
    libc.so.6 => /lib/libc.so.6 (0x00446000)
    /lib/ld-linux.so.2 (0x00a28000)

它显然可以找到它,但这种联系是:

czajnik@czajnik:~/z$ ln -s libtest.so.2.3.4 libtest.so.2
czajnik@czajnik:~/z$ LD_LIBRARY_PATH=. ldd ./test
    linux-gate.so.1 =>  (0x00d75000)
    libtest.so.2 => ./libtest.so.2 (0x00e31000)
    libc.so.6 => /lib/libc.so.6 (0x00a5e000)
    /lib/ld-linux.so.2 (0x00378000)

<>Update: 所有这些都是真实的,但我根本不知道版本第3部分的含义。直到最近,我才认为这只是一个拼凑的数字(或类似情况)。 !! http://www.gnu.org/software/libtool/“rel=“noretinger”>libtool。它具有特殊的意义。

第3部分后来变成了age<>em> field,其中说,许多主要版本与目前的相背。

建议阅读:

Idiot s Guide to ABI Versioning

Libtool s versioning system

友情链接