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elf: Add fast path to dlopen for fully-opened maps

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If the map is already fully open (has matching flags and its
own scope allocated), it is not necessary to unprotected memory
during dlopen.
This commit is contained in:
Florian Weimer 2025-02-02 20:10:09 +01:00
parent edc6842bbc
commit b05e78d473
1 changed files with 31 additions and 5 deletions
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36
elf/dl-open.c
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@ -492,6 +492,23 @@ call_dl_init (void *closure)
_dl_init (args->map, args->argc, args->argv, args->env);
}
/* Return true if the object does not need any processing beyond the
l_direct_opencount update. Needs to be kept in sync with the logic
in dl_open_worker_begin after the l->l_searchlist.r_list != NULL check.
MODE is the dlopen mode argument. */
static bool
is_already_fully_open (struct link_map *map, int mode)
{
return (map != NULL /* An existing map was found. */
/* dlopen completed initialization of this map. Maps with
l_type == lt_library start out as partially initialized. */
&& map->l_searchlist.r_list != NULL
/* The object is already in the global scope if requested. */
&& (!(mode & RTLD_GLOBAL) || map->l_global)
/* The object is already NODELETE if requested. */
&& (!(mode & RTLD_NODELETE) || map->l_nodelete_active));
}
static void
dl_open_worker_begin (void *a)
{
@ -513,9 +530,10 @@ dl_open_worker_begin (void *a)
_dl_debug_initialize (0, args->nsid);
/* Load the named object. */
struct link_map *new;
args->map = new = _dl_map_object (args->caller_map, file, lt_loaded, 0,
mode | __RTLD_CALLMAP, args->nsid);
struct link_map *new = args->map;
if (new == NULL)
args->map = new = _dl_map_new_object (args->caller_map, file, lt_loaded, 0,
mode | __RTLD_CALLMAP, args->nsid);
/* If the pointer returned is NULL this means the RTLD_NOLOAD flag is
set and the object is not already loaded. */
@ -532,7 +550,7 @@ dl_open_worker_begin (void *a)
/* This object is directly loaded. */
++new->l_direct_opencount;
/* It was already open. */
/* It was already open. See is_already_fully_open above. */
if (__glibc_unlikely (new->l_searchlist.r_list != NULL))
{
/* Let the user know about the opencount. */
@ -834,7 +852,6 @@ no more namespaces available for dlmopen()"));
struct dl_open_args args;
args.file = file;
args.mode = mode;
args.map = NULL;
args.nsid = nsid;
/* args.libc_already_loaded is always assigned by dl_open_worker
(before any explicit/non-local returns). */
@ -859,6 +876,15 @@ no more namespaces available for dlmopen()"));
else
args.caller_map = NULL;
args.map = _dl_lookup_map (args.nsid, file);
if (is_already_fully_open (args.map, mode))
{
/* We can use the fast path. */
++args.map->l_direct_opencount;
__rtld_lock_unlock_recursive (GL(dl_load_lock));
return args.map;
}
struct dl_exception exception;
int errcode = _dl_catch_exception (&exception, dl_open_worker, &args);