C中的共享库和二进制文件

Question

I took over a fairly large C code. There are lots of legacy binaries that are requiring old version shared libraries. The server has never versions of those exact libraries. I could recompile or setup symbolic links that will connect older versions to new. Setting up symbolic links will take some time - is there any standard or smart way to do this? I am new to this and would appreciate any tips. This is all C and FreeBSD environment.

Thanks.

Answer 1

In general when updating legacy code with new libraries, it is best to perform a check by recompiling the source code against the new libraries and their includes. This will allow you to use the compiler to check for inconsistencies between the old and new libraries in areas such as data types, function signatures, etc.

By recompiling you also are able to check that the new libraries provide all of the dependencies that you need.

Finally, doing a recompile will help you check that you are in fact able to recompile and link everything and have all of the necessary components.

I would feel uncomfortable tying to take a short cut such as using symbolic links.

Answer 2

The shared-library version number is only supposed to be changed when the ABI changes. (Old versions of FreeBSD didn't quite get this right, and it's fixed in more recent versions but only for system libraries!) So the only way to make those applications work properly is to either recompile them, or supply the exact version of the shared library that they were linked against. For programs that only depend on old versions of the FreeBSD system libraries, you can installes the compat[45678]x packages, which provide the versions of the libraries supplied with the specified version of the OS -- but there are significant pitfalls:

1) If some of the libraries your application depends on are linked against newer versions of the standard libraries than your application itself is, the dynamic linker will give you two incompatible copies of the standard library, and things are not likely to work.

2) If your application loads external modules or plug-ins using dlopen(), all bets are off, because these modules are not versioned.

FreeBSD 8 and newer use symbol versioning for the C library and some other important system libraries, so those libraries should never change library version again and ABI compatibility will be preserved. Many third-party developers are not so careful, and will both break ABI without changing the library version, and change the library version without breaking the ABI, so you can't win. (Some developers don't read the documentation and think that the shared-library version number should be the same as the product's version number.)