I've written a small program to measure the 'memory payload' of using shared libraries on Linux. What it shows is the amount of private process memory that is taken by the simple fact of _linking_ a program to a shared object. This corresponds roughly to the following data:
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the specific position-independent-code tables, like the GOT, PLT and DLT. These are automatically generated by the dynamic loader. The more functions the library imports/exports, the bigger these tables are. They also explain why _any_ shared library uses at least 4 KB/process.
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any writable static data used by the library itself.
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finally, any absolute pointer constant found in the library, since these cannot be placed within PIC code. Any C++ shared library is going to have all of its vtables in the .data section for this reason.
Note that this does not include the memory used by the libraries when they're used (e.g. when allocating from the heap with 'malloc').
The code is available here. Python 2.1 or above required.
Results are interesting. On my work system (RedHat 7.3), the biggest "eaters" are the following:
process KB KB per library
count total process
--------------------------------------------------------
8 1312 164 /usr/lib/qt-2.3.1/lib/libqt.so.2.3.1
59 1180 20 /lib/i686/libc-2.2.4.so
8 768 96 /usr/lib/libkdeui.so.3.0.0
18 576 32 /lib/i686/libpthread-0.9.so
5 440 88 /local/dturner/opt/lib/libstdc++.so.5.0.5
19 304 16 /usr/X11R6/lib/libX11.so.6.2
8 256 32 /usr/lib/libkdecore.so.3.0.0
59 236 4 /lib/ld-2.2.4.so
8 224 28 /usr/lib/libstdc++-3-libc6-2-2-2.10.0.so
4 192 48 /lib/libcrypto.so.0.9.6b
...
total payload = 10044 KB
This seems pretty reasonnable, though there are some surprises here (it's an XFCE desktop with only two KDE apps opened, no KDM !). I'd better run the script on more recent distributions to see how they compare however.