Ian Lance Taylor wrote: > Marcus Clyne <maccaday@xxxxxxxxx> writes: > >>>> If a shared object is loaded using dlopen etc and the symbols in its >>>> object aren't used (specifically they are defined elsewhere already >>>> inside that process), is the data in the symbols automatically loaded >>>> into memory or is it skipped (assuming there are no other programs >>>> using those symbols on the system) and the memory available for other >>>> purposes? >>>> >>> If you open a shared library with dlopen, then that library is loaded >>> into memory. This will use up virtual address space. If you don't use >>> the library for anything, then the pages will never be loaded into RAM. >>> >> When the object loaded initially with dlopen(), is there anything >> that's transferred to RAM (e.g. the page where the symbol names are), >> or are they only copied to the swap space directly? If that's the >> case, are they then loaded into RAM when dlsym() is called? > > Most of a shared library is read-only and shared. Those pages are > simply mapped into your virtual address space--no copying occurs. In a > typical shared library, a few pages must be modified by the dynamic > linker when the library is loaded: those pages will be copied into RAM > and modified, and if not referenced will eventually be swapped out. The entry point of the library is, I think, called at dlopen() time. Andrew.
