On Wed, Sep 12, 2018 at 11:27 AM Martin Liška <mli...@suse.cz> wrote: > > On 9/11/18 5:08 PM, Alexander Monakov wrote: > > On Tue, 11 Sep 2018, Martin Liška wrote: > >> I've discussed the topic with Alexander on the Cauldron and we hoped > >> that the issue with unique __gcov_root can be handled with DECL_COMMON in > >> each DSO. > >> Apparently this approach does not work as all DSOs in an executable have > >> eventually > >> just a single instance of the __gcov_root, which is bad. > > > > No, that happens only if they have default visibility. Emitting them with > > "hidden" visibility solves this. > > Ah, ok, thanks. So theoretically that way should work. > > > > >> So that I returned back to catch the root of the failure. It shows that > >> even with > >> -Wl,--dynamic-list-data __gcov_indirect_call_callee point to a different > >> variable > >> among the DSOs. The reason is that the variable is TLS: > > > > (no, that the variable is TLS is not causing the bug; the issue is libraries > > carry public definitions of just one or both variables depending on if they > > have indirect calls or not, and the library state becomes "diverged" when > > one variable gets interposed while the other does not) > > I see, I'm attaching patch that does that. I can confirm your test-case works > fine w/o -Wl,--dynamic-list-data. > > I'm wondering if it will work as well with dlopen/dlsym machinery? Or now > the linker flag will be needed? > > > > >> That said I would like to go this direction. I would be happy to receive > >> a feedback. Then I'll test the patch. > > > > Hm, this TLS change is attacking the issue from a wrong direction. What I > > suggested on the Cauldron as a simple and backportable way of solving this > > is to consolidate the two TLS variables into one TLS struct, which is then > > either interposed or not as a whole. > > Got it, current I prefer the solution.
Sounds good. I notice the code had this before but... + TREE_PUBLIC (ic_tuple_var) = 1; + DECL_EXTERNAL (ic_tuple_var) = 1; + TREE_STATIC (ic_tuple_var) = 1; that's one flag too much?! I suggest to drop DECL_EXTERNAL. Richard. > Martin > > > > > Alexander > > >
