glibc

Branch: master

Author	SHA1	Message	Date
Florian Weimer	849274d48f	elf: Fix force_first handling in dlclose (bug 30981) The force_first parameter was ineffective because the dlclose'd object was not necessarily the first in the maps array. Also enable force_first handling unconditionally, regardless of namespace. The initial object in a namespace should be destructed first, too. The _dl_sort_maps_dfs function had early returns for relocation dependency processing which broke force_first handling, too, and this is fixed in this change as well. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>	2 years ago
Florian Weimer	dd32e1db38	Revert "elf: Always call destructors in reverse constructor order (bug 30785)" This reverts commit `6985865bc3`. Reason for revert: The commit changes the order of ELF destructor calls too much relative to what applications expect or can handle. In particular, during process exit and _dl_fini, after the revert commit, we no longer call the destructors of the main program first; that only happens after some dlopen'ed objects have been destructed. This robs applications of an opportunity to influence destructor order by calling dlclose explicitly from the main program's ELF destructors. A couple of different approaches involving reverse constructor order were tried, and none of them worked really well. It seems we need to keep the dependency sorting in _dl_fini. There is also an ambiguity regarding nested dlopen calls from ELF constructors: Should those destructors run before or after the object that called dlopen? Commit `6985865bc3` used reverse order of the start of ELF constructor calls for destructors, but arguably using completion of constructors is more correct. However, that alone is not sufficient to address application compatibility issues (it does not change _dl_fini ordering at all).	2 years ago
Florian Weimer	6985865bc3	elf: Always call destructors in reverse constructor order (bug 30785) The current implementation of dlclose (and process exit) re-sorts the link maps before calling ELF destructors. Destructor order is not the reverse of the constructor order as a result: The second sort takes relocation dependencies into account, and other differences can result from ambiguous inputs, such as cycles. (The force_first handling in _dl_sort_maps is not effective for dlclose.) After the changes in this commit, there is still a required difference due to dlopen/dlclose ordering by the application, but the previous discrepancies went beyond that. A new global (namespace-spanning) list of link maps, _dl_init_called_list, is updated right before ELF constructors are called from _dl_init. In dl_close_worker, the maps variable, an on-stack variable length array, is eliminated. (VLAs are problematic, and dlclose should not call malloc because it cannot readily deal with malloc failure.) Marking still-used objects uses the namespace list directly, with next and next_idx replacing the done_index variable. After marking, _dl_init_called_list is used to call the destructors of now-unused maps in reverse destructor order. These destructors can call dlopen. Previously, new objects do not have l_map_used set. This had to change: There is no copy of the link map list anymore, so processing would cover newly opened (and unmarked) mappings, unloading them. Now, _dl_init (indirectly) sets l_map_used, too. (dlclose is handled by the existing reentrancy guard.) After _dl_init_called_list traversal, two more loops follow. The processing order changes to the original link map order in the namespace. Previously, dependency order was used. The difference should not matter because relocation dependencies could already reorder link maps in the old code. The changes to _dl_fini remove the sorting step and replace it with a traversal of _dl_init_called_list. The l_direct_opencount decrement outside the loader lock is removed because it appears incorrect: the counter manipulation could race with other dynamic loader operations. tst-audit23 needs adjustments to the changes in LA_ACT_DELETE notifications. The new approach for checking la_activity should make it clearer that la_activty calls come in pairs around namespace updates. The dependency sorting test cases need updates because the destructor order is always the opposite order of constructor order, even with relocation dependencies or cycles present. There is a future cleanup opportunity to remove the now-constant force_first and for_fini arguments from the _dl_sort_maps function. Fixes commit `1df71d32fe` ("elf: Implement force_first handling in _dl_sort_maps_dfs (bug 28937)"). Reviewed-by: DJ Delorie <dj@redhat.com>	3 years ago
Florian Weimer	1df71d32fe	elf: Implement force_first handling in _dl_sort_maps_dfs (bug 28937) The implementation in _dl_close_worker requires that the first element of l_initfini is always this very map (“We are always the zeroth entry, and since we don't include ourselves in the dependency analysis start at 1.”). Rather than fixing that assumption, this commit adds an implementation of the force_first argument to the new dependency sorting algorithm. This also means that the directly dlopen'ed shared object is always initialized last, which is the least surprising behavior in the presence of cycles. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>	4 years ago
Chung-Lin Tang	15a0c5730d	elf: Fix slow DSO sorting behavior in dynamic loader (BZ #17645 ) This second patch contains the actual implementation of a new sorting algorithm for shared objects in the dynamic loader, which solves the slow behavior that the current "old" algorithm falls into when the DSO set contains circular dependencies. The new algorithm implemented here is simply depth-first search (DFS) to obtain the Reverse-Post Order (RPO) sequence, a topological sort. A new l_visited:1 bitfield is added to struct link_map to more elegantly facilitate such a search. The DFS algorithm is applied to the input maps[nmap-1] backwards towards maps[0]. This has the effect of a more "shallow" recursion depth in general since the input is in BFS. Also, when combined with the natural order of processing l_initfini[] at each node, this creates a resulting output sorting closer to the intuitive "left-to-right" order in most cases. Another notable implementation adjustment related to this _dl_sort_maps change is the removing of two char arrays 'used' and 'done' in _dl_close_worker to represent two per-map attributes. This has been changed to simply use two new bit-fields l_map_used:1, l_map_done:1 added to struct link_map. This also allows discarding the clunky 'used' array sorting that _dl_sort_maps had to sometimes do along the way. Tunable support for switching between different sorting algorithms at runtime is also added. A new tunable 'glibc.rtld.dynamic_sort' with current valid values 1 (old algorithm) and 2 (new DFS algorithm) has been added. At time of commit of this patch, the default setting is 1 (old algorithm). Signed-off-by: Chung-Lin Tang <cltang@codesourcery.com> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>	5 years ago
Chung-Lin Tang	e6fd79f379	elf: Testing infrastructure for ld.so DSO sorting (BZ #17645 ) This is the first of a 2-part patch set that fixes slow DSO sorting behavior in the dynamic loader, as reported in BZ #17645. In order to facilitate such a large modification to the dynamic loader, this first patch implements a testing framework for validating shared object sorting behavior, to enable comparison between old/new sorting algorithms, and any later enhancements. This testing infrastructure consists of a Python script scripts/dso-ordering-test.py' which takes in a description language, consisting of strings that describe a set of link dependency relations between DSOs, and generates testcase programs and Makefile fragments to automatically test the described situation, for example: a->b->c->d # four objects linked one after another a->[bc]->d;b->c # a depends on b and c, which both depend on d, # b depends on c (b,c linked to object a in fixed order) a->b->c;{+a;%a;-a} # a, b, c serially dependent, main program uses # dlopen/dlsym/dlclose on object a a->b->c;{}!->[abc] # a, b, c serially dependent; multiple tests generated # to test all permutations of a, b, c ordering linked # to main program (Above is just a short description of what the script can do, more documentation is in the script comments.) Two files containing several new tests, elf/dso-sort-tests-[12].def are added, including test scenarios for BZ #15311 and Redhat issue #1162810 [1]. Due to the nature of dynamic loader tests, where the sorting behavior and test output occurs before/after main(), generating testcases to use support/test-driver.c does not suffice to control meaningful timeout for ld.so. Therefore a new utility program 'support/test-run-command', based on test-driver.c/support_test_main.c has been added. This does the same testcase control, but for a program specified through a command-line rather than at the source code level. This utility is used to run the dynamic loader testcases generated by dso-ordering-test.py. [1] https://bugzilla.redhat.com/show_bug.cgi?id=1162810 Signed-off-by: Chung-Lin Tang <cltang@codesourcery.com> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>	5 years ago

6 Commits (master)