Analyzing this question I found out some things about behavior of weak symbol resolution in the context of dynamic loading (dlopen) on Linux. Now I'm looking for the specifications governing this.
Let's take an example. Suppose there is a program a which dynamically loads libraries b.so and c.so, in that order. If c.so depends on two other libraries foo.so (actually libgcc.so in that example) and bar.so (actually libpthread.so), then usually symbols exported by bar.so can be used to satisfy weak symbol linkages in foo.so. But if b.so also depends on foo.so but not on bar.so, then these weak symbols will apparently not be linked against bar.so. It seems as if foo.so inkages only look for symbols from a and b.so and all their dependencies.
This makes sense, to some degree, since otherwise loading c.so might change the behavior of foo.so at some point where b.so has already been using the library. On the other hand, in the question that got me started this caused quite a bit of trouble, so I wonder whether there is a way around this problem. And in order to find ways around, I first need a good understanding about the very exact details how symbol resolution in these cases is specified.
What is the specification or other technical document to define correct behavior in these scenarios?