diff options
| -rw-r--r-- | NEWS | 9 | ||||
| -rw-r--r-- | elf/dl-close.c | 34 | ||||
| -rw-r--r-- | elf/dl-deps.c | 7 | ||||
| -rw-r--r-- | elf/dl-fini.c | 3 | ||||
| -rw-r--r-- | elf/dl-sort-maps.c | 208 | ||||
| -rw-r--r-- | elf/dl-support.c | 2 | ||||
| -rw-r--r-- | elf/dl-sysdep.c | 3 | ||||
| -rw-r--r-- | elf/dl-tunables.list | 9 | ||||
| -rw-r--r-- | elf/dso-sort-tests-1.def | 2 | ||||
| -rw-r--r-- | elf/rtld.c | 3 | ||||
| -rw-r--r-- | elf/tst-rtld-list-tunables.exp | 1 | ||||
| -rw-r--r-- | include/link.h | 5 | ||||
| -rw-r--r-- | manual/tunables.texi | 11 | ||||
| -rw-r--r-- | sysdeps/generic/ldsodefs.h | 14 |
14 files changed, 269 insertions, 42 deletions
@@ -51,6 +51,15 @@ Major new features: * The ISO C2X macro _PRINTF_NAN_LEN_MAX has been added to <stdio.h>. +* A new DSO sorting algorithm has been added in the dynamic linker that uses + topological sorting by depth-first search (DFS), solving performance issues + of the existing sorting algorithm when encountering particular circular + object dependency cases. + +* A new tunable, glibc.rtld.dynamic_sort, can be used to select between the two + DSO sorting algorithms. The default setting of '1' uses the current existing + algorithm, while a value of '2' selects the new DFS-based algorithm. + Deprecated and removed features, and other changes affecting compatibility: * The r_version update in the debugger interface makes the glibc binary diff --git a/elf/dl-close.c b/elf/dl-close.c index cfe0f1c..4f5cfcc 100644 --- a/elf/dl-close.c +++ b/elf/dl-close.c @@ -167,8 +167,6 @@ _dl_close_worker (struct link_map *map, bool force) bool any_tls = false; const unsigned int nloaded = ns->_ns_nloaded; - char used[nloaded]; - char done[nloaded]; struct link_map *maps[nloaded]; /* Run over the list and assign indexes to the link maps and enter @@ -176,24 +174,21 @@ _dl_close_worker (struct link_map *map, bool force) 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); - /* Prepare the bitmaps. */ - memset (used, '\0', sizeof (used)); - memset (done, '\0', sizeof (done)); - /* Keep track of the lowest index link map we have covered already. */ int done_index = -1; while (++done_index < nloaded) { struct link_map *l = maps[done_index]; - if (done[done_index]) + if (l->l_map_done) /* Already handled. */ continue; @@ -204,12 +199,12 @@ _dl_close_worker (struct link_map *map, bool force) /* See CONCURRENCY NOTES in cxa_thread_atexit_impl.c to know why acquire is sufficient and correct. */ && atomic_load_acquire (&l->l_tls_dtor_count) == 0 - && !used[done_index]) + && !l->l_map_used) continue; /* We need this object and we handle it now. */ - done[done_index] = 1; - used[done_index] = 1; + l->l_map_used = 1; + l->l_map_done = 1; /* Signal the object is still needed. */ l->l_idx = IDX_STILL_USED; @@ -225,9 +220,9 @@ _dl_close_worker (struct link_map *map, bool force) { assert ((*lp)->l_idx >= 0 && (*lp)->l_idx < nloaded); - if (!used[(*lp)->l_idx]) + if (!(*lp)->l_map_used) { - used[(*lp)->l_idx] = 1; + (*lp)->l_map_used = 1; /* If we marked a new object as used, and we've already processed it, then we need to go back and process again from that point forward to @@ -250,9 +245,9 @@ _dl_close_worker (struct link_map *map, bool force) { assert (jmap->l_idx >= 0 && jmap->l_idx < nloaded); - if (!used[jmap->l_idx]) + if (!jmap->l_map_used) { - used[jmap->l_idx] = 1; + jmap->l_map_used = 1; if (jmap->l_idx - 1 < done_index) done_index = jmap->l_idx - 1; } @@ -262,8 +257,7 @@ _dl_close_worker (struct link_map *map, bool force) /* 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 + (nsid == LM_ID_BASE), nloaded - (nsid == LM_ID_BASE), - used + (nsid == LM_ID_BASE), true); + _dl_sort_maps (maps, nloaded, (nsid == LM_ID_BASE), true); /* Call all termination functions at once. */ #ifdef SHARED @@ -280,7 +274,7 @@ _dl_close_worker (struct link_map *map, bool force) /* All elements must be in the same namespace. */ assert (imap->l_ns == nsid); - if (!used[i]) + if (!imap->l_map_used) { assert (imap->l_type == lt_loaded && !imap->l_nodelete_active); @@ -333,7 +327,7 @@ _dl_close_worker (struct link_map *map, bool force) if (i < first_loaded) first_loaded = i; } - /* Else used[i]. */ + /* Else imap->l_map_used. */ else if (imap->l_type == lt_loaded) { struct r_scope_elem *new_list = NULL; @@ -560,7 +554,7 @@ _dl_close_worker (struct link_map *map, bool force) for (unsigned int i = first_loaded; i < nloaded; ++i) { struct link_map *imap = maps[i]; - if (!used[i]) + if (!imap->l_map_used) { assert (imap->l_type == lt_loaded); diff --git a/elf/dl-deps.c b/elf/dl-deps.c index 087a49b..237d963 100644 --- a/elf/dl-deps.c +++ b/elf/dl-deps.c @@ -613,10 +613,9 @@ Filters not supported with LD_TRACE_PRELINKING")); /* If libc.so.6 is the main map, it participates in the sort, so that the relocation order is correct regarding libc.so.6. */ - if (l_initfini[0] == GL (dl_ns)[l_initfini[0]->l_ns].libc_map) - _dl_sort_maps (l_initfini, nlist, NULL, false); - else - _dl_sort_maps (&l_initfini[1], nlist - 1, NULL, false); + _dl_sort_maps (l_initfini, nlist, + (l_initfini[0] != GL (dl_ns)[l_initfini[0]->l_ns].libc_map), + false); /* Terminate the list of dependencies. */ l_initfini[nlist] = NULL; diff --git a/elf/dl-fini.c b/elf/dl-fini.c index 6dbdfe4..c683884 100644 --- a/elf/dl-fini.c +++ b/elf/dl-fini.c @@ -92,8 +92,7 @@ _dl_fini (void) /* 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 + (ns == LM_ID_BASE), nmaps - (ns == LM_ID_BASE), - NULL, true); + _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 diff --git a/elf/dl-sort-maps.c b/elf/dl-sort-maps.c index d217702..a274ed6 100644 --- a/elf/dl-sort-maps.c +++ b/elf/dl-sort-maps.c @@ -16,16 +16,24 @@ License along with the GNU C Library; if not, see <https://www.gnu.org/licenses/>. */ +#include <assert.h> #include <ldsodefs.h> +#include <elf/dl-tunables.h> +/* Note: this is the older, "original" sorting algorithm, being used as + default up to 2.35. -/* Sort array MAPS according to dependencies of the contained objects. - Array USED, if non-NULL, is permutated along MAPS. If FOR_FINI this is - called for finishing an object. */ -void -_dl_sort_maps (struct link_map **maps, unsigned int nmaps, char *used, - bool for_fini) + Sort array MAPS according to dependencies of the contained objects. + If FOR_FINI is true, this is called for finishing an object. */ +static void +_dl_sort_maps_original (struct link_map **maps, unsigned int nmaps, + unsigned int skip, bool for_fini) { + /* Allows caller to do the common optimization of skipping the first map, + usually the main binary. */ + maps += skip; + nmaps -= skip; + /* A list of one element need not be sorted. */ if (nmaps <= 1) return; @@ -66,14 +74,6 @@ _dl_sort_maps (struct link_map **maps, unsigned int nmaps, char *used, (k - i) * sizeof (maps[0])); maps[k] = thisp; - if (used != NULL) - { - char here_used = used[i]; - memmove (&used[i], &used[i + 1], - (k - i) * sizeof (used[0])); - used[k] = here_used; - } - if (seen[i + 1] > nmaps - i) { ++i; @@ -120,3 +120,183 @@ _dl_sort_maps (struct link_map **maps, unsigned int nmaps, char *used, next:; } } + +#if !HAVE_TUNABLES +/* In this case, just default to the original algorithm. */ +strong_alias (_dl_sort_maps_original, _dl_sort_maps); +#else + +/* We use a recursive function due to its better clarity and ease of + implementation, as well as faster execution speed. We already use + alloca() for list allocation during the breadth-first search of + dependencies in _dl_map_object_deps(), and this should be on the + same order of worst-case stack usage. + + Note: the '*rpo' parameter is supposed to point to one past the + last element of the array where we save the sort results, and is + decremented before storing the current map at each level. */ + +static void +dfs_traversal (struct link_map ***rpo, struct link_map *map, + bool *do_reldeps) +{ + if (map->l_visited) + return; + + map->l_visited = 1; + + if (map->l_initfini) + { + for (int i = 0; map->l_initfini[i] != NULL; i++) + { + struct link_map *dep = map->l_initfini[i]; + if (dep->l_visited == 0 + && dep->l_main_map == 0) + dfs_traversal (rpo, dep, do_reldeps); + } + } + + if (__glibc_unlikely (do_reldeps != NULL && map->l_reldeps != NULL)) + { + /* Indicate that we encountered relocation dependencies during + traversal. */ + *do_reldeps = true; + + for (int m = map->l_reldeps->act - 1; m >= 0; m--) + { + struct link_map *dep = map->l_reldeps->list[m]; + if (dep->l_visited == 0 + && dep->l_main_map == 0) + dfs_traversal (rpo, dep, do_reldeps); + } + } + + *rpo -= 1; + **rpo = map; +} + +/* Topologically sort array MAPS according to dependencies of the contained + objects. */ + +static void +_dl_sort_maps_dfs (struct link_map **maps, unsigned int nmaps, + unsigned int skip __attribute__ ((unused)), bool for_fini) +{ + for (int i = nmaps - 1; i >= 0; i--) + maps[i]->l_visited = 0; + + /* We apply DFS traversal for each of maps[i] until the whole total order + is found and we're at the start of the Reverse-Postorder (RPO) sequence, + which is a topological sort. + + We go from maps[nmaps - 1] backwards towards maps[0] at this level. + Due to the breadth-first search (BFS) ordering we receive, going + backwards usually gives a more shallow depth-first recursion depth, + adding more stack usage safety. Also, combined with the natural + processing order of l_initfini[] at each node during DFS, this maintains + an ordering closer to the original link ordering in the sorting results + under most simpler cases. + + Another reason we order the top level backwards, it that maps[0] is + usually exactly the main object of which we're in the midst of + _dl_map_object_deps() processing, and maps[0]->l_initfini[] is still + blank. If we start the traversal from maps[0], since having no + dependencies yet filled in, maps[0] will always be immediately + incorrectly placed at the last place in the order (first in reverse). + Adjusting the order so that maps[0] is last traversed naturally avoids + this problem. + + Further, the old "optimization" of skipping the main object at maps[0] + from the call-site (i.e. _dl_sort_maps(maps+1,nmaps-1)) is in general + no longer valid, since traversing along object dependency-links + may "find" the main object even when it is not included in the initial + order (e.g. a dlopen()'ed shared object can have circular dependencies + linked back to itself). In such a case, traversing N-1 objects will + create a N-object result, and raise problems. + + To summarize, just passing in the full list, and iterating from back + to front makes things much more straightforward. */ + + /* Array to hold RPO sorting results, before we copy back to maps[]. */ + struct link_map *rpo[nmaps]; + + /* The 'head' position during each DFS iteration. Note that we start at + one past the last element due to first-decrement-then-store (see the + bottom of above dfs_traversal() routine). */ + struct link_map **rpo_head = &rpo[nmaps]; + + bool do_reldeps = false; + bool *do_reldeps_ref = (for_fini ? &do_reldeps : NULL); + + for (int i = nmaps - 1; i >= 0; i--) + { + dfs_traversal (&rpo_head, maps[i], do_reldeps_ref); + + /* We can break early if all objects are already placed. */ + if (rpo_head == rpo) + goto end; + } + assert (rpo_head == rpo); + + end: + /* Here we may do a second pass of sorting, using only l_initfini[] + static dependency links. This is avoided if !FOR_FINI or if we didn't + find any reldeps in the first DFS traversal. + + The reason we do this is: while it is unspecified how circular + dependencies should be handled, the presumed reasonable behavior is to + have destructors to respect static dependency links as much as possible, + overriding reldeps if needed. And the first sorting pass, which takes + l_initfini/l_reldeps links equally, may not preserve this priority. + + Hence we do a 2nd sorting pass, taking only DT_NEEDED links into account + (see how the do_reldeps argument to dfs_traversal() is NULL below). */ + if (do_reldeps) + { + for (int i = nmaps - 1; i >= 0; i--) + rpo[i]->l_visited = 0; + + struct link_map **maps_head = &maps[nmaps]; + for (int i = nmaps - 1; i >= 0; i--) + { + dfs_traversal (&maps_head, rpo[i], NULL); + + /* We can break early if all objects are already placed. + The below memcpy is not needed in the do_reldeps case here, + since we wrote back to maps[] during DFS traversal. */ + if (maps_head == maps) + return; + } + assert (maps_head == maps); + return; + } + + memcpy (maps, rpo, sizeof (struct link_map *) * nmaps); +} + +void +_dl_sort_maps_init (void) +{ + int32_t algorithm = TUNABLE_GET (glibc, rtld, dynamic_sort, int32_t, NULL); + GLRO(dl_dso_sort_algo) = algorithm == 1 ? dso_sort_algorithm_original + : dso_sort_algorithm_dfs; +} + +void +_dl_sort_maps (struct link_map **maps, unsigned int nmaps, + unsigned int skip, bool for_fini) +{ + /* It can be tempting to use a static function pointer to store and call + the current selected sorting algorithm routine, but experimentation + shows that current processors still do not handle indirect branches + that efficiently, plus a static function pointer will involve + PTR_MANGLE/DEMANGLE, further impairing performance of small, common + input cases. A simple if-case with direct function calls appears to + be the fastest. */ + if (__glibc_likely (GLRO(dl_dso_sort_algo) == dso_sort_algorithm_original)) + _dl_sort_maps_original (maps, nmaps, skip, for_fini); + else + _dl_sort_maps_dfs (maps, nmaps, skip, for_fini); +} + +#endif /* HAVE_TUNABLES. */ diff --git a/elf/dl-support.c b/elf/dl-support.c index d99c1f1..98d5d8d 100644 --- a/elf/dl-support.c +++ b/elf/dl-support.c @@ -166,6 +166,8 @@ size_t _dl_phnum; uint64_t _dl_hwcap; uint64_t _dl_hwcap2; +enum dso_sort_algorithm _dl_dso_sort_algo; + /* The value of the FPU control word the kernel will preset in hardware. */ fpu_control_t _dl_fpu_control = _FPU_DEFAULT; diff --git a/elf/dl-sysdep.c b/elf/dl-sysdep.c index 2c684c2..4dc366e 100644 --- a/elf/dl-sysdep.c +++ b/elf/dl-sysdep.c @@ -231,6 +231,9 @@ _dl_sysdep_start (void **start_argptr, __tunables_init (_environ); + /* Initialize DSO sorting algorithm after tunables. */ + _dl_sort_maps_init (); + #ifdef DL_SYSDEP_INIT DL_SYSDEP_INIT; #endif diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list index 8ddd4a2..46ffb23 100644 --- a/elf/dl-tunables.list +++ b/elf/dl-tunables.list @@ -156,4 +156,13 @@ glibc { security_level: SXID_IGNORE } } + + rtld { + dynamic_sort { + type: INT_32 + minval: 1 + maxval: 2 + default: 1 + } + } } diff --git a/elf/dso-sort-tests-1.def b/elf/dso-sort-tests-1.def index 873ddf5..5f7f18e 100644 --- a/elf/dso-sort-tests-1.def +++ b/elf/dso-sort-tests-1.def @@ -62,5 +62,5 @@ output: b>a>{}<a<b # 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 -xfail_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=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];} @@ -1391,6 +1391,9 @@ dl_main (const ElfW(Phdr) *phdr, main_map->l_name = (char *) ""; *user_entry = main_map->l_entry; + /* Set bit indicating this is the main program map. */ + main_map->l_main_map = 1; + #ifdef HAVE_AUX_VECTOR /* Adjust the on-stack auxiliary vector so that it looks like the binary was executed directly. */ diff --git a/elf/tst-rtld-list-tunables.exp b/elf/tst-rtld-list-tunables.exp index 9f66c52..9bf5727 100644 --- a/elf/tst-rtld-list-tunables.exp +++ b/elf/tst-rtld-list-tunables.exp @@ -10,5 +10,6 @@ glibc.malloc.tcache_max: 0x0 (min: 0x0, max: 0x[f]+) glibc.malloc.tcache_unsorted_limit: 0x0 (min: 0x0, max: 0x[f]+) glibc.malloc.top_pad: 0x0 (min: 0x0, max: 0x[f]+) glibc.malloc.trim_threshold: 0x0 (min: 0x0, max: 0x[f]+) +glibc.rtld.dynamic_sort: 1 (min: 1, max: 2) glibc.rtld.nns: 0x4 (min: 0x1, max: 0x10) glibc.rtld.optional_static_tls: 0x200 (min: 0x0, max: 0x[f]+) diff --git a/include/link.h b/include/link.h index 484ee6c..c1c382c 100644 --- a/include/link.h +++ b/include/link.h @@ -181,6 +181,11 @@ struct link_map unsigned int l_init_called:1; /* Nonzero if DT_INIT function called. */ unsigned int l_global:1; /* Nonzero if object in _dl_global_scope. */ unsigned int l_reserved:2; /* Reserved for internal use. */ + unsigned int l_main_map:1; /* Nonzero for the map of the main program. */ + unsigned int l_visited:1; /* Used internally for map dependency + graph traversal. */ + unsigned int l_map_used:1; /* These two bits are used during traversal */ + unsigned int l_map_done:1; /* of maps in _dl_close_worker. */ unsigned int l_phdr_allocated:1; /* Nonzero if the data structure pointed to by `l_phdr' is allocated. */ unsigned int l_soname_added:1; /* Nonzero if the SONAME is for sure in diff --git a/manual/tunables.texi b/manual/tunables.texi index 658547c..10f4d75 100644 --- a/manual/tunables.texi +++ b/manual/tunables.texi @@ -309,6 +309,17 @@ changed once allocated at process startup. The default allocation of optional static TLS is 512 bytes and is allocated in every thread. @end deftp +@deftp Tunable glibc.rtld.dynamic_sort +Sets the algorithm to use for DSO sorting, valid values are @samp{1} and +@samp{2}. For value of @samp{1}, an older O(n^3) algorithm is used, which is +long time tested, but may have performance issues when dependencies between +shared objects contain cycles due to circular dependencies. When set to the +value of @samp{2}, a different algorithm is used, which implements a +topological sort through depth-first search, and does not exhibit the +performance issues of @samp{1}. + +The default value of this tunable is @samp{1}. +@end deftp @node Elision Tunables @section Elision Tunables diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h index 0410f77..65a6a51 100644 --- a/sysdeps/generic/ldsodefs.h +++ b/sysdeps/generic/ldsodefs.h @@ -245,6 +245,13 @@ enum allowmask }; +/* DSO sort algorithm to use (check dl-sort-maps.c). */ +enum dso_sort_algorithm + { + dso_sort_algorithm_original, + dso_sort_algorithm_dfs + }; + struct audit_ifaces { void (*activity) (uintptr_t *, unsigned int); @@ -678,6 +685,8 @@ struct rtld_global_ro platforms. */ EXTERN uint64_t _dl_hwcap2; + EXTERN enum dso_sort_algorithm _dl_dso_sort_algo; + #ifdef SHARED /* We add a function table to _rtld_global which is then used to call the function instead of going through the PLT. The result @@ -1104,7 +1113,7 @@ extern void _dl_fini (void) attribute_hidden; /* Sort array MAPS according to dependencies of the contained objects. */ extern void _dl_sort_maps (struct link_map **maps, unsigned int nmaps, - char *used, bool for_fini) attribute_hidden; + unsigned int skip, bool for_fini) attribute_hidden; /* The dynamic linker calls this function before and having changing any shared object mappings. The `r_state' member of `struct r_debug' @@ -1235,6 +1244,9 @@ extern struct link_map * _dl_get_dl_main_map (void) # endif #endif +/* Initialize the DSO sort algorithm to use. */ +extern void _dl_sort_maps_init (void) attribute_hidden; + /* Initialization of libpthread for statically linked applications. If libpthread is not linked in, this is an empty function. */ void __pthread_initialize_minimal (void) weak_function; |