On 20/09/10 02:17, Miles Bader wrote: > Ian Lance Taylor <iant@xxxxxxxxxx> writes: >> What happens here is that when using -fPIC symbol interposition is >> permitted for any globally visible symbol. That is, the -fPIC code is >> presumed to wind up in a shared library. An executable may override any >> function in a shared library. The code in the shared library which >> calls that function is then expected to call the definition in the >> executable instead. It follows that when using -fPIC the compiler may >> not inline any call to a globally visible function, because that would >> prevent symbol interposition. > > Hmm, I guess this makes sense. > > It would definitely be nice to have a more precise description in a > document somewhere though. > > I'd think it would also be good to have a way of disabling this > particular side-effect -- e.g., for non-shared-library uses of shared > objects, like loadable modules/plugins etc, which presumably don't aim > to provide the same guarantees that shared libraries do. It's actually part of the C standard: there may only be one definition of any symbol, whether that symbol refers to a function or to data. So, for every visible symbol X in a program, &X must be the same, no matter who is asking. All manner of things break without this. Andrew.
