问题
A little background: I'm trying to build an AVR binary for an embedded sensor system, and I'm running close to my size limit. I use a few external libraries to help me, but they are rather large when compiled into one object per library. I want to pull these into smaller objects so only the functionality I need is linked into my program. I've already managed to drop the binary size by 2k by splitting up a large library.
It would help a lot to know which objects are being used at each stage of the game so I can split them more efficiently. Is there a way to make ld print which objects it's linking?
回答1:
I'm not sure about the object level, but I believe you might be able to tackle this on the symbol level using CFLAGS="-fdata-sections -ffunction-sections" and LDFLAGS="-Wl,--gc-sections -Wl,--print-gc-sections". This should get rid of the code for all unreferenced symbols, and display the removed symbols to you as well which might be useful if for some reason you decide to go back to the object file level and want to identify object files only containing removed symbols.
To be more precise, the compiler flags I quoted will ask the compiler to place each function or global variable in a section for itself, and the --gc-sections linker flag will then remove all the sections which have not been used. It might be that each object file contains its own sections, even if the functions therein all share a single section. In that case the linker flag alone should do what you ask for: eliminate whole objects which are not used. The gcc manual states that the compiler flags will increase the object size, and although I hope that the final executable should not be affected by this, I don't know for sure, so you should give the LDFLAGS="-Wl,--gc-sections by itself a try in any case.
The listed option names might be useful keywords to search on stackoverflow for other suggestions on how to reduce the size of the binary. gc-sections e.g. yields 62 matches at the moment.
来源：https://stackoverflow.com/questions/10577512/can-gnu-ld-be-instructed-to-print-which-o-files-are-needed-during-a-link