From 20a86d1f340dcc25636acfbdf9f3ca45f4004b1e Mon Sep 17 00:00:00 2001 From: Alexander Kabaev Date: Fri, 28 Jan 2011 23:44:57 +0000 Subject: [PATCH] Eliminate the use of symlook_needed function in favor of DAGS. Place elements on DAG lists in breadth-first order. This allows us to walk pre-built list in all cases where breadth-first dependency chain enumeration is required. Fix dlsym on special handle obtained by dlopen(NULL, ...) to do what comment claims it does. Take advantage of recently added symlook_global function to iterate over main objects and global DAGs lists properly in search of a symbol. Since rtld itself provides part of the global namespace, search rtld_obj too. Remove recursion from init_dag and symlook_needed functions. Use symlook_needed for ELF filtee processing only and change lookup order used in the function to match the order used by Solaris runtime linker under same circumstances. While there, fix weak symbol handling in the loop so that we return the first weak symbol definition if no strong one was found, instead of the last one. Reviewed by: kib MFC after: 1 month --- libexec/rtld-elf/rtld.c | 116 +++++++++++++++++----------------------- 1 file changed, 48 insertions(+), 68 deletions(-) diff --git a/libexec/rtld-elf/rtld.c b/libexec/rtld-elf/rtld.c index e560175660c8..11ef84774a47 100644 --- a/libexec/rtld-elf/rtld.c +++ b/libexec/rtld-elf/rtld.c @@ -93,7 +93,6 @@ static void *fill_search_info(const char *, size_t, void *); static char *find_library(const char *, const Obj_Entry *); static const char *gethints(void); static void init_dag(Obj_Entry *); -static void init_dag1(Obj_Entry *, Obj_Entry *, DoneList *); static void init_rtld(caddr_t, Elf_Auxinfo **); static void initlist_add_neededs(Needed_Entry *, Objlist *); static void initlist_add_objects(Obj_Entry *, Obj_Entry **, Objlist *); @@ -1331,30 +1330,35 @@ gethints(void) static void init_dag(Obj_Entry *root) { + const Needed_Entry *needed; + const Objlist_Entry *elm; DoneList donelist; if (root->dag_inited) return; donelist_init(&donelist); - init_dag1(root, root, &donelist); + + /* Root object belongs to own DAG. */ + objlist_push_tail(&root->dldags, root); + objlist_push_tail(&root->dagmembers, root); + donelist_check(&donelist, root); + + /* + * Add dependencies of root object to DAG in breadth order + * by exploiting the fact that each new object get added + * to the tail of the dagmembers list. + */ + STAILQ_FOREACH(elm, &root->dagmembers, link) { + for (needed = elm->obj->needed; needed != NULL; needed = needed->next) { + if (needed->obj == NULL || donelist_check(&donelist, needed->obj)) + continue; + objlist_push_tail(&needed->obj->dldags, root); + objlist_push_tail(&root->dagmembers, needed->obj); + } + } root->dag_inited = true; } -static void -init_dag1(Obj_Entry *root, Obj_Entry *obj, DoneList *dlp) -{ - const Needed_Entry *needed; - - if (donelist_check(dlp, obj)) - return; - - objlist_push_tail(&obj->dldags, root); - objlist_push_tail(&root->dagmembers, obj); - for (needed = obj->needed; needed != NULL; needed = needed->next) - if (needed->obj != NULL) - init_dag1(root, needed->obj, dlp); -} - /* * Initialize the dynamic linker. The argument is the address at which * the dynamic linker has been mapped into memory. The primary task of @@ -2320,32 +2324,28 @@ do_dlsym(void *handle, const char *name, void *retaddr, const Ver_Entry *ve, donelist_init(&donelist); if (obj->mainprog) { - /* Search main program and all libraries loaded by it. */ - res = symlook_list(&req, &list_main, &donelist); + /* Handle obtained by dlopen(NULL, ...) implies global scope. */ + res = symlook_global(&req, &donelist); if (res == 0) { def = req.sym_out; defobj = req.defobj_out; - } else { - /* - * We do not distinguish between 'main' object and - * global scope. If symbol is not defined by objects - * loaded at startup, continue search among - * dynamically loaded objects with RTLD_GLOBAL scope. - */ - res = symlook_list(&req, &list_global, &donelist); + } + /* + * Search the dynamic linker itself, and possibly resolve the + * symbol from there. This is how the application links to + * dynamic linker services such as dlopen. + */ + if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) { + res = symlook_obj(&req, &obj_rtld); if (res == 0) { def = req.sym_out; defobj = req.defobj_out; } } - } else { - Needed_Entry fake; - + } + else { /* Search the whole DAG rooted at the given object. */ - fake.next = NULL; - fake.obj = (Obj_Entry *)obj; - fake.name = 0; - res = symlook_needed(&req, &fake, &donelist); + res = symlook_list(&req, &obj->dagmembers, &donelist); if (res == 0) { def = req.sym_out; defobj = req.defobj_out; @@ -2960,54 +2960,34 @@ symlook_list(SymLook *req, const Objlist *objlist, DoneList *dlp) } /* - * Search the symbol table of a shared object and all objects needed - * by it for a symbol of the given name. Search order is - * breadth-first. Returns a pointer to the symbol, or NULL if no - * definition was found. + * Search the chain of DAGS cointed to by the given Needed_Entry + * for a symbol of the given name. Each DAG is scanned completely + * before advancing to the next one. Returns a pointer to the symbol, + * or NULL if no definition was found. */ static int symlook_needed(SymLook *req, const Needed_Entry *needed, DoneList *dlp) { - const Elf_Sym *def, *def_w; + const Elf_Sym *def; const Needed_Entry *n; - const Obj_Entry *defobj, *defobj1; + const Obj_Entry *defobj; SymLook req1; int res; - def = def_w = NULL; + def = NULL; defobj = NULL; symlook_init_from_req(&req1, req); for (n = needed; n != NULL; n = n->next) { - if (n->obj == NULL || donelist_check(dlp, n->obj) || - (res = symlook_obj(&req1, n->obj)) != 0) + if (n->obj == NULL || + (res = symlook_list(&req1, &n->obj->dagmembers, dlp)) != 0) continue; - def = req1.sym_out; - defobj = req1.defobj_out; - if (ELF_ST_BIND(def->st_info) != STB_WEAK) { - req->defobj_out = defobj; - req->sym_out = def; - return (0); + if (def == NULL || ELF_ST_BIND(req1.sym_out->st_info) != STB_WEAK) { + def = req1.sym_out; + defobj = req1.defobj_out; + if (ELF_ST_BIND(def->st_info) != STB_WEAK) + break; } } - /* - * There we come when either symbol definition is not found in - * directly needed objects, or found symbol is weak. - */ - for (n = needed; n != NULL; n = n->next) { - if (n->obj == NULL) - continue; - res = symlook_needed(&req1, n->obj->needed, dlp); - if (res != 0) - continue; - def_w = req1.sym_out; - defobj1 = req1.defobj_out; - if (def == NULL || ELF_ST_BIND(def_w->st_info) != STB_WEAK) { - def = def_w; - defobj = defobj1; - } - if (ELF_ST_BIND(def_w->st_info) != STB_WEAK) - break; - } if (def != NULL) { req->sym_out = def; req->defobj_out = defobj;