* [PATCH 2/2] Revert "elf: Always call destructors in reverse constructor order (bug 30785)"
2023-10-06 9:21 [PATCH 0/2] Revert "elf: Always call destructors in reverse constructor order (bug 30785)" Florian Weimer
2023-10-06 9:21 ` [PATCH 1/2] Revert "elf: Fix compile error with -DNDEBUG [BZ #18755]" Florian Weimer
@ 2023-10-06 9:21 ` Florian Weimer
2023-10-06 10:37 ` Andreas Schwab
2023-10-18 8:14 ` Andreas Schwab
2023-10-06 9:25 ` [PATCH 0/2] " Andreas K. Huettel
2 siblings, 2 replies; 9+ messages in thread
From: Florian Weimer @ 2023-10-06 9:21 UTC (permalink / raw)
To: libc-alpha
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 <ldsodefs.h>
#include <elf-initfini.h>
-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>{}<a<b
# Complex example from Bugzilla #15311, under-linked and with circular
-# relocation(dynamic) dependencies. For both sorting algorithms, the
-# destruction order is the reverse of the construction order, and
-# relocation dependencies are not taken into account.
+# relocation(dynamic) dependencies. While this is technically unspecified, the
+# presumed reasonable practical behavior is for the destructor order to respect
+# the static DT_NEEDED links (here this means the 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[<g<f<e<a<b<c<d];}
+output(glibc.rtld.dynamic_sort=1): {+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[<a<c<d<g<f<b<e];}
+output(glibc.rtld.dynamic_sort=2): {+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[<g<f<a<b<c<d<e];}
# Test that even in the presence of dependency loops involving dlopen'ed
# object, that object is initialized last (and not unloaded prematurely).
-# Final destructor order is the opposite of constructor order.
+# Final destructor order is indeterminate due to the cycle.
tst-bz28937: {+a;+b;-b;+c;%c};a->a1;a->a2;a2->a;b->b1;c->a1;c=>a1
-output: {+a[a2>a1>a>];+b[b1>b>];-b[<b<b1];+c[c>];%c(a1());}<c<a<a1<a2
+output(glibc.rtld.dynamic_sort=1): {+a[a2>a1>a>];+b[b1>b>];-b[<b<b1];+c[c>];%c(a1());}<a<a2<c<a1
+output(glibc.rtld.dynamic_sort=2): {+a[a2>a1>a>];+b[b1>b>];-b[<b<b1];+c[c>];%c(a1());}<a2<a<c<a1
diff --git a/elf/tst-audit23.c b/elf/tst-audit23.c
index 503699c36a..bb7d66c385 100644
--- a/elf/tst-audit23.c
+++ b/elf/tst-audit23.c
@@ -98,8 +98,6 @@ do_test (int argc, char *argv[])
char *lname;
uintptr_t laddr;
Lmid_t lmid;
- uintptr_t cookie;
- uintptr_t namespace;
bool closed;
} objs[max_objs] = { [0 ... max_objs-1] = { .closed = false } };
size_t nobjs = 0;
@@ -119,9 +117,6 @@ do_test (int argc, char *argv[])
size_t buffer_length = 0;
while (xgetline (&buffer, &buffer_length, out))
{
- *strchrnul (buffer, '\n') = '\0';
- printf ("info: subprocess output: %s\n", buffer);
-
if (startswith (buffer, "la_activity: "))
{
uintptr_t cookie;
@@ -130,26 +125,29 @@ do_test (int argc, char *argv[])
&cookie);
TEST_COMPARE (r, 2);
+ /* The cookie identifies the object at the head of the link map,
+ so we only add a new namespace if it changes from the previous
+ one. This works since dlmopen is the last in the test body. */
+ if (cookie != last_act_cookie && last_act_cookie != -1)
+ TEST_COMPARE (last_act, LA_ACT_CONSISTENT);
+
if (this_act == LA_ACT_ADD && acts[nacts] != cookie)
{
- /* The cookie identifies the object at the head of the
- link map, so we only add a new namespace if it
- changes from the previous one. This works since
- dlmopen is the last in the test body. */
- if (cookie != last_act_cookie && last_act_cookie != -1)
- TEST_COMPARE (last_act, LA_ACT_CONSISTENT);
-
acts[nacts++] = cookie;
last_act_cookie = cookie;
}
- /* LA_ACT_DELETE is called multiple times for each
- namespace, depending on destruction order. */
+ /* The LA_ACT_DELETE is called in the reverse order of LA_ACT_ADD
+ at program termination (if the tests adds a dlclose or a library
+ with extra dependencies this will need to be adapted). */
else if (this_act == LA_ACT_DELETE)
- last_act_cookie = cookie;
+ {
+ last_act_cookie = acts[--nacts];
+ TEST_COMPARE (acts[nacts], cookie);
+ acts[nacts] = 0;
+ }
else if (this_act == LA_ACT_CONSISTENT)
{
TEST_COMPARE (cookie, last_act_cookie);
- last_act_cookie = -1;
/* LA_ACT_DELETE must always be followed by an la_objclose. */
if (last_act == LA_ACT_DELETE)
@@ -181,8 +179,6 @@ do_test (int argc, char *argv[])
objs[nobjs].lname = lname;
objs[nobjs].laddr = laddr;
objs[nobjs].lmid = lmid;
- objs[nobjs].cookie = cookie;
- objs[nobjs].namespace = last_act_cookie;
objs[nobjs].closed = false;
nobjs++;
@@ -205,12 +201,6 @@ do_test (int argc, char *argv[])
if (strcmp (lname, objs[i].lname) == 0 && lmid == objs[i].lmid)
{
TEST_COMPARE (objs[i].closed, false);
- TEST_COMPARE (objs[i].cookie, cookie);
- if (objs[i].namespace == -1)
- /* No LA_ACT_ADD before the first la_objopen call. */
- TEST_COMPARE (acts[0], last_act_cookie);
- else
- TEST_COMPARE (objs[i].namespace, last_act_cookie);
objs[i].closed = true;
break;
}
@@ -219,7 +209,11 @@ do_test (int argc, char *argv[])
/* la_objclose should be called after la_activity(LA_ACT_DELETE) for
the closed object's namespace. */
TEST_COMPARE (last_act, LA_ACT_DELETE);
- seen_first_objclose = true;
+ if (!seen_first_objclose)
+ {
+ TEST_COMPARE (last_act_cookie, cookie);
+ seen_first_objclose = true;
+ }
}
}
diff --git a/include/link.h b/include/link.h
index c6af095d87..adb3886193 100644
--- a/include/link.h
+++ b/include/link.h
@@ -276,10 +276,6 @@ struct link_map
/* List of object in order of the init and fini calls. */
struct link_map **l_initfini;
- /* Linked list of objects in reverse ELF constructor execution
- order. Head of list is stored in _dl_init_called_list. */
- struct link_map *l_init_called_next;
-
/* List of the dependencies introduced through symbol binding. */
struct link_map_reldeps
{
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 82c5383c7e..9b50ddd09f 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -1037,10 +1037,6 @@ extern int _dl_check_map_versions (struct link_map *map, int verbose,
extern void _dl_init (struct link_map *main_map, int argc, char **argv,
char **env) attribute_hidden;
-/* List of ELF objects in reverse order of their constructor
- invocation. */
-extern struct link_map *_dl_init_called_list attribute_hidden;
-
/* Call the finalizer functions of all shared objects whose
initializer functions have completed. */
extern void _dl_fini (void) attribute_hidden;
--
2.41.0
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