On Tue, May 28, 2013 at 9:02 PM, Ryan Johnson <ryan.john...@cs.utoronto.ca> wrote: > > Maybe I misunderstood... there's currently a (very small) cache > (unwind-dw2-fde-dip.c) that lives behind the loader mutex. It contains 8 > entries and each entry holds the start and end addresses for one loaded > object, along with a pointer to the eh_frame_header. The cache resides in > static storage, and so accessing it is always safe. > > I think what you're saying is that the p_eh_frame_hdr field could end up > with a dangling pointer due to a dlclose call?
Yes, that can happen. > If so, my argument is that, as long as the cache is up to date as of the > start of unwind, any attempt to access a dangling p_eh_frame_hdr means that > in-use code was dlclosed, in which case unwind is guaranteed to fail anyway. > The failure would just have different symptoms with such a cache in place. > > Am I missing something? I think you're right about that. But what happens if the entry is not in the cache? Or, do you mean you want to look in the cache before calling dl_iterate_phdr? That should be safe but of course you still need a lock as multiple threads can be manipulating the cache at the same time. Ian
