2013/12/3 Sam Varshavchik <mrsam@xxxxxxxxxxxxxxx>: > Hatt Tom writes: > >> Here is one example : >> >> First, I linked liba.so into executable target by the compiler >> command "g++ -la " at linking stage . >> >> then ,I use dlopen to load liba.so in the executable's process . >> >> At this time ,the reference count of liba.so is 2 , am I right ? > > > Right. > > And if you think you can just dlclose() it an extra time, think again. It > won't work. For at least two reasons. > > 1) dlopen() returns an opaque handle for each open. Opening the same .so is > going to give you a technically different handle, and because you can only > dlclose() a handle that you've opened, and you do not have a handle that was > used to, essentially, dlopen the directly-linked library, you can't do it. > > 2) Your existing executable has resolved the external symbols to your .so > already (via a process that's equivalent to dlsym(), even before your > executable ran). Even if you somehow manage to close it, and dlopen it back, > the existing linkage remains what it is. Hillarity ensues. So if I link that .so against my executable by "g++ -l " command ,then I can not dlclose it fully in process at all ? Tp dlclose it fully , I must not link it by compiler ,but manually use dlopen and dlsym to resolve the external symbols . But if so ,how to make the compiler not to compalain "not reference to symbol xxx" at compiling stage ? Thanks! > > So, you have no choice but to dlopen() your library, right from the start. > You have no other options. > > >> >> >> >> 2013/12/3 Sam Varshavchik <mrsam@xxxxxxxxxxxxxxx>: >> > Hatt Tom writes: >> > >> >> Thanks ! The problem has been resolved . >> >> >> >> And hereis one question I should get to be clear of . if I link one >> >> .so into one executeable file , would this increase the reference >> >> count by one already ? so dlclose would not unload that .so until the >> >> reference count decrease to zero . >> > >> > >> > Correct. >> > >> > >> >> >> >> 2013/12/2 Sam Varshavchik <mrsam@xxxxxxxxxxxxxxx>: >> >> > Hatt Tom writes: >> >> > >> >> >> If I use dlsym() to load the address manually ,will GOT be needed >> >> >> any >> >> >> more ? >> >> > >> >> > >> >> > If you always use dlopen(), and the dlsym() to call methods from a >> >> > .so, >> >> > you >> >> > don't really need to link to it directly, any more, so this is a moot >> >> > point. >> >> > >> >> > >> >> > >> >> >> 2013/12/2 Nicholas Mc Guire <der.herr@xxxxxxx>: >> >> >> > On Mon, 02 Dec 2013, Hatt Tom wrote: >> >> >> > >> >> >> >> And also : why cannot I dlclose a .so that I've linked my >> >> >> >> executable >> >> >> >> to, in the usual fashion. >> >> >> >> >> >> >> >> is it because the reference count of that .so would not alwayes >> >> >> >> to >> >> >> >> be >> >> >> >> zero ? >> >> >> >> >> >> >> >> It seems puzzling to me ? >> >> >> >> >> >> >> > how would you ensure consistency of the GOT ? >> >> >> > I think the problem is that you would end up with invalid >> >> >> > addresses >> >> >> > in >> >> >> > the GOT >> >> >> > as they were setup by ld based on link-time information. >> >> >> > >> >> >> > thx! >> >> >> > hofrat >> >> >> >> >> >> >> >> >> >> >> >> -- >> >> >> Best Regards! >> >> >> >> >> >> >> >> -- >> >> Best Regards! >> >> >> >> -- >> Best Regards! -- Best Regards!
