that itself uses multiple c++ shared libraries that make use of
templates. Actually I get an segmentation fault during dlclose().
The reason for this lays in the algorithm how dlclose() handles running
the destructors and unmapping the libraries memory. Currently this
looks somehow like this:
foreach $library in @libraries {
if (--$library->refcount) == 0) {
$library->callDestructors();
$library->unmap();
}
}
In general this is not wrong if there are no weak symbols involved.
When using C++ templates it may happen that there are multiple instances
of the same template with the same template parameters in different
libraries. To make the linker happy all these symbols are marked as weak
by the compiler and the runtime linker chooses the physical memory
location based on some magic.
Now look again at the algorithm above. What happens in my case is that
one of the libraries uses some code and data of a template instance in
its destructors that was placed in memory of a library that got unmapped
earlier. This directly results in a segmentation fault because of a
reference to unmapped memory.
I made a check with current glibc and here everything is working fine.
Strace showed me that first all destructors of all libraries were
running and then all memory of all libraries is unmapped. So I think the
algorithm should be splitted in uClibc too:
foreach $library in @libraries {
if (--$library->refcount) == 0) {
$library->callDestructors();
}
}
foreach $library in @libraries {
if ($library->refcount) == 0) {
$library->unmap();
}
}
What do you think?
I hope this gets fixed soon. Thx!
Currently I have no simple example ready but I hope the description is
clear enough to understand the problem. If you really want example code
to demonstrate the problem I can try to hack something.
libdl.patch [^] (522 bytes) 09-17-08 02:26 
