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elf: Remove version assert in check_match in elf/dl-lookup.c
This case is detected early in the elf/dl-version.c consistency checks. (These checks could be disabled in the future to allow the removal of symbol versioning from objects.) Commitf0b2132b35
("ld.so: Support moving versioned symbols between sonames [BZ #24741]) removed another call to _dl_name_match_p. The _dl_check_caller function no longer exists, and the remaining calls to _dl_name_match_p happen under the loader lock. This means that atomic accesses are no longer required for the l_libname list. This supersedes commit395be7c218
("elf: Fix data race in _dl_name_match_p [BZ #21349]").
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@ -429,23 +429,7 @@ add_name_to_object (struct link_map *l, const char *name)
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newname->name = memcpy (newname + 1, name, name_len);
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newname->next = NULL;
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newname->dont_free = 0;
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/* CONCURRENCY NOTES:
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Make sure the initialization of newname happens before its address is
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read from the lastp->next store below.
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GL(dl_load_lock) is held here (and by other writers, e.g. dlclose), so
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readers of libname_list->next (e.g. _dl_check_caller or the reads above)
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can use that for synchronization, however the read in _dl_name_match_p
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may be executed without holding the lock during _dl_runtime_resolve
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(i.e. lazy symbol resolution when a function of library l is called).
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The release MO store below synchronizes with the acquire MO load in
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_dl_name_match_p. Other writes need to synchronize with that load too,
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however those happen either early when the process is single threaded
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(dl_main) or when the library is unloaded (dlclose) and the user has to
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synchronize library calls with unloading. */
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atomic_store_release (&lastp->next, newname);
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lastp->next = newname;
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}
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/* Standard search directories. */
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@ -93,22 +93,9 @@ check_match (const char *const undef_name,
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const ElfW(Half) *verstab = map->l_versyms;
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if (version != NULL)
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{
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if (__glibc_unlikely (verstab == NULL))
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{
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/* We need a versioned symbol but haven't found any. If
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this is the object which is referenced in the verneed
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entry it is a bug in the library since a symbol must
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not simply disappear.
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It would also be a bug in the object since it means that
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the list of required versions is incomplete and so the
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tests in dl-version.c haven't found a problem.*/
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assert (version->filename == NULL
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|| ! _dl_name_match_p (version->filename, map));
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/* Otherwise we accept the symbol. */
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}
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else
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/* If there is no version information, accept the symbol. This
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can happen during symbol interposition. */
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if (__glibc_likely (verstab != NULL))
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{
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/* We can match the version information or use the
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default one if it is not hidden. */
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@ -75,9 +75,7 @@ _dl_name_match_p (const char *name, const struct link_map *map)
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if (strcmp (name, runp->name) == 0)
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return 1;
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else
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/* Synchronize with the release MO store in add_name_to_object.
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See CONCURRENCY NOTES in add_name_to_object in dl-load.c. */
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runp = atomic_load_acquire (&runp->next);
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runp = runp->next;
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return 0;
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}
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