问题
I have an application dependent on many libraries. I am building everything from sources on an ubuntu machine. I want to remove any function/class that is not required by an application. Is there any tool to help with that?
P.S. I want to remove source code from the library not just symbols from object files.
回答1:
Standard strip utility was created exactly for this.
回答2:
I have now researched this a bit in the context of my own project and decided this was worth a full answer rather than just a comment. This answer is based on Apple's toolchain on macOS (which uses clang, rather than gcc), but I think things work in much the same way for both.
The key to this is enabling 'link time optimization' when building your libraries and executable(s). The mechanics of this are actually very simple - just pass -flto to gcc and ld on the command line. This has two effects:
- Code (functions / methods) in object files or archives that is never called is omitted from the final executable.
- The linker performs the sort of optimisations that the compiler can perform (such as function inlining), but with knowledge that extends across compilation unit boundaries.
It won't help you if you are linking against a shared library, but it might help if that shared library links with other (static) libraries which contain code that the shared library never calls.
On the upside, this reduced the size of my final executable by about 5%, which I'm pleased about. YMMV.
On the downside, my object files roughly doubled in size and sometimes link times increased dramatically (by something like a factor of 100). Then, if I re-linked, it was much faster. This behaviour might be a peculiarity of Apple's toolchain however. Perhaps it is stashing away some build intermediates somewhere on the first link. In any case, if you only enable this option for release builds it should not be a major issue.
There are more details of the full set of gcc command line options that control optimisation here: https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html. Search that page for flto to narrow down your search.
And for a glimpse behind the scenes, see: https://gcc.gnu.org/onlinedocs/gccint/LTO-Overview.html
Edit:
A bit more information about link times. Apple's linker creates some huge files in a directory called LTOCache when you link. I've not seen these before today so these look to be the build intermediates that speed up linking second time around. As for my initial link being so slow, this may in part be due to the fact that, in my case, these are created on an SMB server. But then again, the CPU was maxed out so maybe not.
回答3:
OK, now that I understand the OP's requirements better I have another answer for this that I think might better suit his needs. I think the way to tackle this is with a code coverage tool. After all, the problem is identifying what you can safely get rid of it. Actually stripping it out is easy.
My IDE (Visual Studio) has one of these built in but I think the OP is using gcc so the first port of call appears to be gcov. There are a number of commercial options, but they are expensive. There's also a potentially useful post here.
The other thing you need, of course, is a program that exercises all the parts of the library that you want to keep to give you a coverage report to work from, but it sounds like the OP already has that. A good IDE will also help as it makes navigating around the code so much easier. In Visual Studio, I find Jump to Definition and quick and easy 'bookmarking' to be key features.
来源：https://stackoverflow.com/questions/50501342/stripping-c-library-of-not-required-code-for-an-application