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20:59 -!- Irssi: #openbsd-daily: Total of 74 nicks [0 ops, 0 halfops, 0 voices, 74 normal]
21:00 < mulander> --- code read: dlopen 5 ---
21:00 < mulander> *** goal: finish reading dlopen ***
21:00 < mulander> previous reads:
21:00 < mulander> - https://junk.tintagel.pl/openbsd-daily-dlopen-1.txt
21:00 < mulander> - https://junk.tintagel.pl/openbsd-daily-dlopen-2.txt
21:00 < mulander> - https://junk.tintagel.pl/openbsd-daily-dlopen-3.txt
21:01 < mulander> - https://junk.tintagel.pl/openbsd-daily-dlopen-4.txt
21:01 < mulander> handy links:
21:01 < mulander> - https://man.openbsd.org/dlopen
21:01 < mulander> - http://man.openbsd.org/ld.so
21:01 < mulander> dlopen header file
21:02 < mulander> - http://bxr.su/OpenBSD/include/dlfcn.h
21:03 < mulander> we went up our call stack on the last read back to the top-level dlopen
21:03 < mulander> so we resume from http://bxr.su/OpenBSD/libexec/ld.so/dlfcn.c#83
21:03 < mulander> at this point we have an elf object loaded
21:03 < mulander> and symbols set to the resolver
21:03 < mulander> unless bind now was specified
21:04 < mulander> so the next significant call in dlfcn.c
21:04 < mulander> 90    _dl_link_dlopen(object);
21:05 < mulander> http://bxr.su/OpenBSD/libexec/ld.so/library_subr.c#429
21:06 < mulander> we saw calls to this before when loading the elf object
21:06 < mulander> the comment  /* this add_object should not be here, XXX */ is interesting but we will not dive into it
21:07 < mulander> DL_DEB calls are just debug output
21:07 < mulander> next up
21:07 < mulander> 107    if ((failed = _dl_load_dep_libs(object, obj_flags, 0)) == 1) {
21:08 < mulander> http://bxr.su/OpenBSD/libexec/ld.so/loader.c#271
21:09 < mulander> so I assume this loads any .so files that our dlopened .so file might depend on
21:09 < mulander> 284        /* propagate DF_1_NOW to deplibs (can be set by dynamic tags) */
21:09 < mulander> 285        depflags = flags | (dynobj->obj_flags & DF_1_NOW);
21:09 < mulander> if the main dlopened library is binded on load we push that downards to dependencies
21:10 < mulander> next
21:10 < mulander> 287        for (dynp = dynobj->load_dyn; dynp->d_tag; dynp++) {
21:10 < mulander> 288            if (dynp->d_tag == DT_NEEDED) {
21:10 < mulander> 289                libcount++;
21:10 < mulander> 290            }
21:10 < mulander> 291        }
21:10 < mulander> we see how many libs we have to load
21:12 < mulander> we build up a list of dependencies
21:12 < mulander> then randomise it
21:12 < mulander> and loop over each required element loading it with a call we already went through in detail
21:12 < mulander> http://bxr.su/OpenBSD/libexec/ld.so/loader.c#335
21:14 < mulander> after loading we see
21:14 < mulander> 352            for (loop = 0; loop < libcount; loop++) {
21:14 < mulander> 353                _dl_add_object(liblist[loop].depobj);
21:14 < mulander> 354                _dl_link_child(liblist[loop].depobj, dynobj);
21:14 < mulander> 355            }
21:14 < mulander> http://bxr.su/OpenBSD/libexec/ld.so/resolve.c#54
21:15 < mulander> just the loaded objects book keeping
21:15 < mulander> http://bxr.su/OpenBSD/libexec/ld.so/library_subr.c#510
21:15 < mulander> again dependency book keeping
21:16 < mulander> and the last two calls
21:16 < mulander> 362    /* add first object manually */
21:16 < mulander> 363    _dl_link_grpsym(object, 1);
21:16 < mulander> 364    _dl_cache_grpsym_list_setup(object);
21:17 < mulander> boil down to
21:17 < mulander> http://bxr.su/OpenBSD/libexec/ld.so/library_subr.c#_dl_cache_grpsym_list
21:17 < mulander> explained by the comment
21:17 < mulander> 577    /*
21:17 < mulander> 578     * grpsym_list is an ordered list of all child libs of the
21:17 < mulander> 579     * _dl_loading_object with no dups. The order is equivalent
21:17 < mulander> 580     * to a breadth-first traversal of the child list without dups.
21:17 < mulander> 581     */
21:19 < mulander> so we return back to dlopen
21:20 < mulander> http://bxr.su/OpenBSD/libexec/ld.so/dlfcn.c#107
21:22 < mulander> if we failed to load
21:22 < mulander> http://bxr.su/OpenBSD/libexec/ld.so/dlfcn.c#_dl_real_close
21:23 < mulander> (failed to load deps)
21:23 < mulander> we proceed to clean up the main dlopened library
21:23 < mulander> running destructors, freeing memory, unloading the lib etc
21:23 < mulander> and doing all the ref counting book keeping
21:24 < mulander> otherwise if we succeeded
21:25 < mulander> again we see a chunk of code responsible for tracing of what's loaded
21:27 < mulander> if loading went fine we do relocation and call constructors from the loaded lib
21:28 < mulander> finally we reach the end of dlopen
21:28 < rsadowski> Hi All
21:28 < mulander> o/ rsadowski 
21:28 < mulander> so that leaves us done with dlopen itself and needing to decide where to go next for further reads
21:28  * mulander digs up notes
21:29 < mulander> > dlctl() provides an interface similar to ioctl(2) to control several aspects of the run-time linker's operation. This interface is currently under development.
21:30 < mulander> > 76#define DL_LAZY     RTLD_LAZY   /* Compat */
21:30 < mulander> regarding dlctl
21:31 < mulander> we could investigate what 'under development means' and if the interface is at all used anywhere
21:31 < mulander> and compare it to other bsd and nix family os'es
21:31 < mulander> regarding DL_LAZY
21:31 < mulander> we could see where it came from, if it's used etc.
21:32 < mulander> or alternatively we could change the topic completely away from dlopen and dynamic linking
21:34 < mulander> http://www.strawpoll.me/13735633
21:34 < mulander> please vote for the next read
21:34 < mulander> as usual next friday 19:00 UTC based on the poll results
21:34 < mulander> if voting for 'something other' please send me an email with a topic suggestion - it's quite easy to get a hold of my mail
21:35 < mulander> and I will count email suggestions with a higher weight than poll votes.
21:35 < mulander> --- DONE ---