Warner Losh: But wasn't it tsort that did the heavy lifting to get things in order? ar c foo.a `tsort *.o` Ranlib just made it fast by adding an index.. ==== There's a little more than that to ranlib. Without ranlib, ld made a single pass through each library, loading the modules that resolved unresolved symbols. If a module itself had unresolved symbols (as many do) and some of those symbols were defined in a module ld had already passed, you were out of luck, unless you explicitly told ld to run a second pass, e.g. cc x.o y.o -la -la. Hence the importance of explicit ordering when building the library archive, and the usefulness of tsort. Ranlib makes a list of all the .o file in this archive and the global symbols defined or used by each module, and places the list first in the archive. If ld is (as it was) changed to recognize the index, it can then make a list of all the object files needed from this archive, even if needed only by some file it will load from the same archive, then collect all required modules in a single pass. Ld could all along have just made two passes through the library, one to assemble the same list ranlib did in advance, a second to load the files. (Or perhaps a first pass to load what it knows it needs and assemble the list, and a second only if necessary.) Presumably it didn't both to make ld simpler and because disk I/O was much slower back then (especially on a heavily-loaded time-sharing system, something far less common today). I suspect it would work fine just to do it that way today. Nowadays ranlib is no longer a separate program: ar recognizes object files and maintains an index if any are present. I never especially liked that; ar is in principle a general tool so why should it have a special case for one type of file? But in practice I don't know anyone who uses ar for anything except libraries any more (everyone uses tar for the general case, since it does a better job). Were I to wave flags over the matter I'd rather push to ditch ar entirely save for compatibility with the past, move to using tar rather than ar for object libraries, and let ld do two passes when necessary rather than requiring that libraries be specially prepared. As I say, I think modern systems are fast enough that that would work fine. Norman Wilson Toronto ON