From patchwork Fri Oct 6 09:21:36 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Florian Weimer X-Patchwork-Id: 77203 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 99E40385CC9F for ; Fri, 6 Oct 2023 09:21:58 +0000 (GMT) X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 6F5DE3857359 for ; Fri, 6 Oct 2023 09:21:40 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 6F5DE3857359 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1696584100; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=tJnLJd37Rkh0VISmTlHCVLwKTJ05VBbnftMf+xroGbY=; b=BJzAC+GGLRlw9/HsRUia7QM4belmYbPYap2EbBa9iitW6oulIY/5PtQKrDd9vAHmI+rbLG Gkgf+hWF3psWCsf/Dx65RZPqn9jxxqKF0Pp6sECmGqkjAkpZvCnqjV08/YVVCHzdD9ndbA FQE8mdOqeyx+TvGRpr8xmxs+J2xOhnc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-217-vfXbY24wPvWa-Qj21xuAMQ-1; Fri, 06 Oct 2023 05:21:38 -0400 X-MC-Unique: vfXbY24wPvWa-Qj21xuAMQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 75871858280 for ; Fri, 6 Oct 2023 09:21:38 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.2.16.57]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C699C215670B for ; Fri, 6 Oct 2023 09:21:37 +0000 (UTC) From: Florian Weimer To: libc-alpha@sourceware.org Subject: [PATCH 2/2] Revert "elf: Always call destructors in reverse constructor order (bug 30785)" In-Reply-To: Message-ID: <71ea27cd61b93937b13dbc17fbe1db5dab7b9566.1696583991.git.fweimer@redhat.com> References: X-From-Line: 71ea27cd61b93937b13dbc17fbe1db5dab7b9566 Mon Sep 17 00:00:00 2001 Date: Fri, 06 Oct 2023 11:21:36 +0200 User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-Spam-Status: No, score=-10.6 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org This reverts commit 6985865bc3ad5b23147ee73466583dd7fdf65892. 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 exist 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 6985865bc3ad5b2314 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). --- elf/dl-close.c | 113 ++++++++++----------------- elf/dl-fini.c | 152 ++++++++++++++++++++++++------------- elf/dl-init.c | 16 ---- elf/dso-sort-tests-1.def | 19 +++-- elf/tst-audit23.c | 44 +++++------ include/link.h | 4 - sysdeps/generic/ldsodefs.h | 4 - 7 files changed, 173 insertions(+), 179 deletions(-) diff --git a/elf/dl-close.c b/elf/dl-close.c index c9a7d06577..1c7a861db1 100644 --- a/elf/dl-close.c +++ b/elf/dl-close.c @@ -138,31 +138,30 @@ _dl_close_worker (struct link_map *map, bool force) bool any_tls = false; const unsigned int nloaded = ns->_ns_nloaded; + struct link_map *maps[nloaded]; - /* Run over the list and assign indexes to the link maps. */ + /* Run over the list and assign indexes to the link maps and enter + them into the MAPS array. */ int idx = 0; for (struct link_map *l = ns->_ns_loaded; l != NULL; l = l->l_next) { l->l_map_used = 0; l->l_map_done = 0; l->l_idx = idx; + maps[idx] = l; ++idx; } assert (idx == nloaded); - /* Keep marking link maps until no new link maps are found. */ - for (struct link_map *l = ns->_ns_loaded; l != NULL; ) + /* Keep track of the lowest index link map we have covered already. */ + int done_index = -1; + while (++done_index < nloaded) { - /* next is reset to earlier link maps for remarking. */ - struct link_map *next = l->l_next; - int next_idx = l->l_idx + 1; /* next->l_idx, but covers next == NULL. */ + struct link_map *l = maps[done_index]; if (l->l_map_done) - { - /* Already handled. */ - l = next; - continue; - } + /* Already handled. */ + continue; /* Check whether this object is still used. */ if (l->l_type == lt_loaded @@ -172,10 +171,7 @@ _dl_close_worker (struct link_map *map, bool force) acquire is sufficient and correct. */ && atomic_load_acquire (&l->l_tls_dtor_count) == 0 && !l->l_map_used) - { - l = next; - continue; - } + continue; /* We need this object and we handle it now. */ l->l_map_used = 1; @@ -202,11 +198,8 @@ _dl_close_worker (struct link_map *map, bool force) already processed it, then we need to go back and process again from that point forward to ensure we keep all of its dependencies also. */ - if ((*lp)->l_idx < next_idx) - { - next = *lp; - next_idx = next->l_idx; - } + if ((*lp)->l_idx - 1 < done_index) + done_index = (*lp)->l_idx - 1; } } @@ -226,65 +219,44 @@ _dl_close_worker (struct link_map *map, bool force) if (!jmap->l_map_used) { jmap->l_map_used = 1; - if (jmap->l_idx < next_idx) - { - next = jmap; - next_idx = next->l_idx; - } + if (jmap->l_idx - 1 < done_index) + done_index = jmap->l_idx - 1; } } } - - l = next; } - /* Call the destructors in reverse constructor order, and remove the - closed link maps from the list. */ - for (struct link_map **init_called_head = &_dl_init_called_list; - *init_called_head != NULL; ) + /* Sort the entries. We can skip looking for the binary itself which is + at the front of the search list for the main namespace. */ + _dl_sort_maps (maps, nloaded, (nsid == LM_ID_BASE), true); + + /* Call all termination functions at once. */ + bool unload_any = false; + bool scope_mem_left = false; + unsigned int unload_global = 0; + unsigned int first_loaded = ~0; + for (unsigned int i = 0; i < nloaded; ++i) { - struct link_map *imap = *init_called_head; + struct link_map *imap = maps[i]; - /* _dl_init_called_list is global, to produce a global odering. - Ignore the other namespaces (and link maps that are still used). */ - if (imap->l_ns != nsid || imap->l_map_used) - init_called_head = &imap->l_init_called_next; - else + /* All elements must be in the same namespace. */ + assert (imap->l_ns == nsid); + + if (!imap->l_map_used) { assert (imap->l_type == lt_loaded && !imap->l_nodelete_active); - /* _dl_init_called_list is updated at the same time as - l_init_called. */ - assert (imap->l_init_called); - - if (imap->l_info[DT_FINI_ARRAY] != NULL - || imap->l_info[DT_FINI] != NULL) + /* Call its termination function. Do not do it for + half-cooked objects. Temporarily disable exception + handling, so that errors are fatal. */ + if (imap->l_init_called) _dl_catch_exception (NULL, _dl_call_fini, imap); #ifdef SHARED /* Auditing checkpoint: we remove an object. */ _dl_audit_objclose (imap); #endif - /* Unlink this link map. */ - *init_called_head = imap->l_init_called_next; - } - } - - - bool unload_any = false; - bool scope_mem_left = false; - unsigned int unload_global = 0; - - /* For skipping un-unloadable link maps in the second loop. */ - struct link_map *first_loaded = ns->_ns_loaded; - /* Iterate over the namespace to find objects to unload. Some - unloadable objects may not be on _dl_init_called_list due to - dlopen failure. */ - for (struct link_map *imap = first_loaded; imap != NULL; imap = imap->l_next) - { - if (!imap->l_map_used) - { /* This object must not be used anymore. */ imap->l_removed = 1; @@ -295,8 +267,8 @@ _dl_close_worker (struct link_map *map, bool force) ++unload_global; /* Remember where the first dynamically loaded object is. */ - if (first_loaded == NULL) - first_loaded = imap; + if (i < first_loaded) + first_loaded = i; } /* Else imap->l_map_used. */ else if (imap->l_type == lt_loaded) @@ -432,8 +404,8 @@ _dl_close_worker (struct link_map *map, bool force) imap->l_loader = NULL; /* Remember where the first dynamically loaded object is. */ - if (first_loaded == NULL) - first_loaded = imap; + if (i < first_loaded) + first_loaded = i; } } @@ -504,11 +476,10 @@ _dl_close_worker (struct link_map *map, bool force) /* Check each element of the search list to see if all references to it are gone. */ - for (struct link_map *imap = first_loaded; imap != NULL; ) + for (unsigned int i = first_loaded; i < nloaded; ++i) { - if (imap->l_map_used) - imap = imap->l_next; - else + struct link_map *imap = maps[i]; + if (!imap->l_map_used) { assert (imap->l_type == lt_loaded); @@ -719,9 +690,7 @@ _dl_close_worker (struct link_map *map, bool force) if (imap == GL(dl_initfirst)) GL(dl_initfirst) = NULL; - struct link_map *next = imap->l_next; free (imap); - imap = next; } } diff --git a/elf/dl-fini.c b/elf/dl-fini.c index e201d36651..9acb64f47c 100644 --- a/elf/dl-fini.c +++ b/elf/dl-fini.c @@ -24,68 +24,116 @@ void _dl_fini (void) { - /* Call destructors strictly in the reverse order of constructors. - This causes fewer surprises than some arbitrary reordering based - on new (relocation) dependencies. None of the objects are - unmapped, so applications can deal with this if their DSOs remain - in a consistent state after destructors have run. */ - - /* Protect against concurrent loads and unloads. */ - __rtld_lock_lock_recursive (GL(dl_load_lock)); - - /* Ignore objects which are opened during shutdown. */ - struct link_map *local_init_called_list = _dl_init_called_list; - - for (struct link_map *l = local_init_called_list; l != NULL; - l = l->l_init_called_next) - /* Bump l_direct_opencount of all objects so that they - are not dlclose()ed from underneath us. */ - ++l->l_direct_opencount; - - /* After this point, everything linked from local_init_called_list - cannot be unloaded because of the reference counter update. */ - __rtld_lock_unlock_recursive (GL(dl_load_lock)); - - /* Perform two passes: One for non-audit modules, one for audit - modules. This way, audit modules receive unload notifications - for non-audit objects, and the destructors for audit modules - still run. */ + /* Lots of fun ahead. We have to call the destructors for all still + loaded objects, in all namespaces. The problem is that the ELF + specification now demands that dependencies between the modules + are taken into account. I.e., the destructor for a module is + called before the ones for any of its dependencies. + + To make things more complicated, we cannot simply use the reverse + order of the constructors. Since the user might have loaded objects + using `dlopen' there are possibly several other modules with its + dependencies to be taken into account. Therefore we have to start + determining the order of the modules once again from the beginning. */ + + /* We run the destructors of the main namespaces last. As for the + other namespaces, we pick run the destructors in them in reverse + order of the namespace ID. */ +#ifdef SHARED + int do_audit = 0; + again: +#endif + for (Lmid_t ns = GL(dl_nns) - 1; ns >= 0; --ns) + { + /* Protect against concurrent loads and unloads. */ + __rtld_lock_lock_recursive (GL(dl_load_lock)); + + unsigned int nloaded = GL(dl_ns)[ns]._ns_nloaded; + /* No need to do anything for empty namespaces or those used for + auditing DSOs. */ + if (nloaded == 0 +#ifdef SHARED + || GL(dl_ns)[ns]._ns_loaded->l_auditing != do_audit +#endif + ) + __rtld_lock_unlock_recursive (GL(dl_load_lock)); + else + { #ifdef SHARED - int last_pass = GLRO(dl_naudit) > 0; - Lmid_t last_ns = -1; - for (int do_audit = 0; do_audit <= last_pass; ++do_audit) + _dl_audit_activity_nsid (ns, LA_ACT_DELETE); #endif - for (struct link_map *l = local_init_called_list; l != NULL; - l = l->l_init_called_next) - { + + /* Now we can allocate an array to hold all the pointers and + copy the pointers in. */ + struct link_map *maps[nloaded]; + + unsigned int i; + struct link_map *l; + assert (nloaded != 0 || GL(dl_ns)[ns]._ns_loaded == NULL); + for (l = GL(dl_ns)[ns]._ns_loaded, i = 0; l != NULL; l = l->l_next) + /* Do not handle ld.so in secondary namespaces. */ + if (l == l->l_real) + { + assert (i < nloaded); + + maps[i] = l; + l->l_idx = i; + ++i; + + /* Bump l_direct_opencount of all objects so that they + are not dlclose()ed from underneath us. */ + ++l->l_direct_opencount; + } + assert (ns != LM_ID_BASE || i == nloaded); + assert (ns == LM_ID_BASE || i == nloaded || i == nloaded - 1); + unsigned int nmaps = i; + + /* Now we have to do the sorting. We can skip looking for the + binary itself which is at the front of the search list for + the main namespace. */ + _dl_sort_maps (maps, nmaps, (ns == LM_ID_BASE), true); + + /* We do not rely on the linked list of loaded object anymore + from this point on. We have our own list here (maps). The + various members of this list cannot vanish since the open + count is too high and will be decremented in this loop. So + we release the lock so that some code which might be called + from a destructor can directly or indirectly access the + lock. */ + __rtld_lock_unlock_recursive (GL(dl_load_lock)); + + /* 'maps' now contains the objects in the right order. Now + call the destructors. We have to process this array from + the front. */ + for (i = 0; i < nmaps; ++i) + { + struct link_map *l = maps[i]; + + if (l->l_init_called) + { + _dl_call_fini (l); #ifdef SHARED - if (GL(dl_ns)[l->l_ns]._ns_loaded->l_auditing != do_audit) - continue; - - /* Avoid back-to-back calls of _dl_audit_activity_nsid for the - same namespace. */ - if (last_ns != l->l_ns) - { - if (last_ns >= 0) - _dl_audit_activity_nsid (last_ns, LA_ACT_CONSISTENT); - _dl_audit_activity_nsid (l->l_ns, LA_ACT_DELETE); - last_ns = l->l_ns; - } + /* Auditing checkpoint: another object closed. */ + _dl_audit_objclose (l); #endif + } - /* There is no need to re-enable exceptions because _dl_fini - is not called from a context where exceptions are caught. */ - _dl_call_fini (l); + /* Correct the previous increment. */ + --l->l_direct_opencount; + } #ifdef SHARED - /* Auditing checkpoint: another object closed. */ - _dl_audit_objclose (l); + _dl_audit_activity_nsid (ns, LA_ACT_CONSISTENT); #endif - } + } + } #ifdef SHARED - if (last_ns >= 0) - _dl_audit_activity_nsid (last_ns, LA_ACT_CONSISTENT); + if (! do_audit && GLRO(dl_naudit) > 0) + { + do_audit = 1; + goto again; + } if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_STATISTICS)) _dl_debug_printf ("\nruntime linker statistics:\n" diff --git a/elf/dl-init.c b/elf/dl-init.c index ffd05b7806..ba4d2fdc85 100644 --- a/elf/dl-init.c +++ b/elf/dl-init.c @@ -21,7 +21,6 @@ #include #include -struct link_map *_dl_init_called_list; static void call_init (struct link_map *l, int argc, char **argv, char **env) @@ -43,21 +42,6 @@ call_init (struct link_map *l, int argc, char **argv, char **env) dependency. */ l->l_init_called = 1; - /* Help an already-running dlclose: The just-loaded object must not - be removed during the current pass. (No effect if no dlclose in - progress.) */ - l->l_map_used = 1; - - /* Record execution before starting any initializers. This way, if - the initializers themselves call dlopen, their ELF destructors - will eventually be run before this object is destructed, matching - that their ELF constructors have run before this object was - constructed. _dl_fini uses this list for audit callbacks, so - register objects on the list even if they do not have a - constructor. */ - l->l_init_called_next = _dl_init_called_list; - _dl_init_called_list = l; - /* Check for object which constructors we do not run here. */ if (__builtin_expect (l->l_name[0], 'a') == '\0' && l->l_type == lt_executable) diff --git a/elf/dso-sort-tests-1.def b/elf/dso-sort-tests-1.def index 61dc54f8ae..4bf9052db1 100644 --- a/elf/dso-sort-tests-1.def +++ b/elf/dso-sort-tests-1.def @@ -53,14 +53,21 @@ tst-dso-ordering10: {}->a->b->c;soname({})=c output: b>a>{}b->c->d order). +# The older dynamic_sort=1 algorithm does not achieve this, while the DFS-based +# dynamic_sort=2 algorithm does, although it is still arguable whether going +# beyond spec to do this is the right thing to do. +# The below expected outputs are what the two algorithms currently produce +# respectively, for regression testing purposes. tst-bz15311: {+a;+e;+f;+g;+d;%d;-d;-g;-f;-e;-a};a->b->c->d;d=>[ba];c=>a;b=>e=>a;c=>f=>b;d=>g=>c -output: {+a[d>c>b>a>];+e[e>];+f[f>];+g[g>];+d[];%d(b(e(a()))a()g(c(a()f(b(e(a()))))));-d[];-g[];-f[];-e[];-a[c>b>a>];+e[e>];+f[f>];+g[g>];+d[];%d(b(e(a()))a()g(c(a()f(b(e(a()))))));-d[];-g[];-f[];-e[];-a[c>b>a>];+e[e>];+f[f>];+g[g>];+d[];%d(b(e(a()))a()g(c(a()f(b(e(a()))))));-d[];-g[];-f[];-e[];-a[a1;a->a2;a2->a;b->b1;c->a1;c=>a1 -output: {+a[a2>a1>a>];+b[b1>b>];-b[];%c(a1());}a1>a>];+b[b1>b>];-b[];%c(a1());}a1>a>];+b[b1>b>];-b[];%c(a1());}