From ba384f6ed9275f3966505f2375b56d169e3dc588 Mon Sep 17 00:00:00 2001 From: Siddhesh Poyarekar Date: Mon, 18 Feb 2013 19:08:21 +0530 Subject: C++11 thread_local destructors support This feature is specifically for the C++ compiler to offload calling thread_local object destructors on thread program exit, to glibc. This is to overcome the possible complication of destructors of thread_local objects getting called after the DSO in which they're defined is unloaded by the dynamic linker. The DSO is marked as 'unloadable' if it has a constructed thread_local object and marked as 'unloadable' again when all the constructed thread_local objects defined in it are destroyed. --- stdlib/Makefile | 12 ++++- stdlib/Versions | 4 ++ stdlib/cxa_thread_atexit_impl.c | 102 ++++++++++++++++++++++++++++++++++++ stdlib/exit.c | 3 ++ stdlib/tst-tls-atexit-lib.c | 36 +++++++++++++ stdlib/tst-tls-atexit.c | 111 ++++++++++++++++++++++++++++++++++++++++ 6 files changed, 266 insertions(+), 2 deletions(-) create mode 100644 stdlib/cxa_thread_atexit_impl.c create mode 100644 stdlib/tst-tls-atexit-lib.c create mode 100644 stdlib/tst-tls-atexit.c (limited to 'stdlib') diff --git a/stdlib/Makefile b/stdlib/Makefile index e2078f8877..6f98c71c64 100644 --- a/stdlib/Makefile +++ b/stdlib/Makefile @@ -34,7 +34,7 @@ routines := \ bsearch qsort msort \ getenv putenv setenv secure-getenv \ exit on_exit atexit cxa_atexit cxa_finalize old_atexit \ - quick_exit at_quick_exit cxa_at_quick_exit \ + quick_exit at_quick_exit cxa_at_quick_exit cxa_thread_atexit_impl \ abs labs llabs \ div ldiv lldiv \ mblen mbstowcs mbtowc wcstombs wctomb \ @@ -71,9 +71,11 @@ tests := tst-strtol tst-strtod testmb testrand testsort testdiv \ tst-makecontext2 tst-strtod6 tst-unsetenv1 \ tst-makecontext3 bug-getcontext bug-fmtmsg1 \ tst-secure-getenv tst-strtod-overflow tst-strtod-round \ - tst-tininess tst-strtod-underflow + tst-tininess tst-strtod-underflow tst-tls-atexit tests-static := tst-secure-getenv +modules-names = tst-tls-atexit-lib + include ../Makeconfig ifeq ($(build-shared),yes) @@ -155,3 +157,9 @@ $(objpfx)bug-getcontext: $(link-libm) $(objpfx)tst-strtod-round: $(link-libm) $(objpfx)tst-tininess: $(link-libm) $(objpfx)tst-strtod-underflow: $(link-libm) + +tst-tls-atexit-lib.so-no-z-defs = yes + +LDFLAGS-tst-tls-atexit = $(common-objpfx)nptl/libpthread.so \ + $(common-objpfx)dlfcn/libdl.so +$(objpfx)tst-tls-atexit.out: $(objpfx)tst-tls-atexit-lib.so diff --git a/stdlib/Versions b/stdlib/Versions index 250bd5fad7..f1777dfcf4 100644 --- a/stdlib/Versions +++ b/stdlib/Versions @@ -106,6 +106,9 @@ libc { GLIBC_2.17 { secure_getenv; } + GLIBC_2.18 { + __cxa_thread_atexit_impl; + } GLIBC_PRIVATE { # functions which have an additional interface since they are # are cancelable. @@ -114,5 +117,6 @@ libc { __abort_msg; # Used from other libraries __libc_secure_getenv; + __call_tls_dtors; } } diff --git a/stdlib/cxa_thread_atexit_impl.c b/stdlib/cxa_thread_atexit_impl.c new file mode 100644 index 0000000000..9638efc7a0 --- /dev/null +++ b/stdlib/cxa_thread_atexit_impl.c @@ -0,0 +1,102 @@ +/* Register destructors for C++ TLS variables declared with thread_local. + Copyright (C) 2012 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#include +#include + +typedef void (*dtor_func) (void *); + +struct dtor_list +{ + dtor_func func; + void *obj; + struct link_map *map; + struct dtor_list *next; +}; + +static __thread struct dtor_list *tls_dtor_list; +static __thread void *dso_symbol_cache; +static __thread struct link_map *lm_cache; + +/* Register a destructor for TLS variables declared with the 'thread_local' + keyword. This function is only called from code generated by the C++ + compiler. FUNC is the destructor function and OBJ is the object to be + passed to the destructor. DSO_SYMBOL is the __dso_handle symbol that each + DSO has at a unique address in its map, added from crtbegin.o during the + linking phase. */ +int +__cxa_thread_atexit_impl (dtor_func func, void *obj, void *dso_symbol) +{ + /* Prepend. */ + struct dtor_list *new = calloc (1, sizeof (struct dtor_list)); + new->func = func; + new->obj = obj; + new->next = tls_dtor_list; + tls_dtor_list = new; + + /* See if we already encountered the DSO. */ + __rtld_lock_lock_recursive (GL(dl_load_lock)); + + if (__builtin_expect (dso_symbol_cache != dso_symbol, 0)) + { + ElfW(Addr) caller = (ElfW(Addr)) dso_symbol; + + struct link_map *l = _dl_find_dso_for_object (caller); + + /* If the address is not recognized the call comes from the main + program (we hope). */ + lm_cache = l ? l : GL(dl_ns)[LM_ID_BASE]._ns_loaded; + } + /* A destructor could result in a thread_local construction and the former + could have cleared the flag. */ + if (lm_cache->l_type == lt_loaded && lm_cache->l_tls_dtor_count == 0) + lm_cache->l_flags_1 |= DF_1_NODELETE; + + new->map = lm_cache; + new->map->l_tls_dtor_count++; + + __rtld_lock_unlock_recursive (GL(dl_load_lock)); + + return 0; +} + +/* Call the destructors. This is called either when a thread returns from the + initial function or when the process exits via the exit(3) function. */ +void +__call_tls_dtors (void) +{ + while (tls_dtor_list) + { + struct dtor_list *cur = tls_dtor_list; + tls_dtor_list = tls_dtor_list->next; + + cur->func (cur->obj); + + __rtld_lock_lock_recursive (GL(dl_load_lock)); + + /* Allow DSO unload if count drops to zero. */ + cur->map->l_tls_dtor_count--; + if (cur->map->l_tls_dtor_count == 0 && cur->map->l_type == lt_loaded) + cur->map->l_flags_1 &= ~DF_1_NODELETE; + + __rtld_lock_unlock_recursive (GL(dl_load_lock)); + + free (cur); + } +} +libc_hidden_def (__call_tls_dtors) diff --git a/stdlib/exit.c b/stdlib/exit.c index e9a2139f4e..2e86caa2d4 100644 --- a/stdlib/exit.c +++ b/stdlib/exit.c @@ -33,6 +33,9 @@ attribute_hidden __run_exit_handlers (int status, struct exit_function_list **listp, bool run_list_atexit) { + /* First, call the TLS destructors. */ + __call_tls_dtors (); + /* We do it this way to handle recursive calls to exit () made by the functions registered with `atexit' and `on_exit'. We call everyone on the list and use the status value in the last diff --git a/stdlib/tst-tls-atexit-lib.c b/stdlib/tst-tls-atexit-lib.c new file mode 100644 index 0000000000..aab28bb607 --- /dev/null +++ b/stdlib/tst-tls-atexit-lib.c @@ -0,0 +1,36 @@ +/* Verify that DSO is unloaded only if its TLS objects are destroyed - the DSO. + Copyright (C) 2012 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +extern void *__dso_handle; + +typedef struct +{ + void *val; +} A; + +/* We only care about the destructor. */ +void A_dtor (void *obj) +{ + ((A *)obj)->val = obj; +} + +void do_foo (void) +{ + static __thread A b; + __cxa_thread_atexit_impl (A_dtor, &b, __dso_handle); +} diff --git a/stdlib/tst-tls-atexit.c b/stdlib/tst-tls-atexit.c new file mode 100644 index 0000000000..b7312cbc84 --- /dev/null +++ b/stdlib/tst-tls-atexit.c @@ -0,0 +1,111 @@ +/* Verify that DSO is unloaded only if its TLS objects are destroyed. + Copyright (C) 2012 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +/* There are two tests in this test case. The first is implicit where it is + assumed that the destructor call on exit of the LOAD function does not + segfault. The other is a verification that after the thread has exited, a + dlclose will unload the DSO. */ + +#include +#include +#include +#include +#include +#include + +void *handle; +pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER; + +void * +load (void *u) +{ + pthread_mutex_lock (&m); + handle = dlopen ("$ORIGIN/tst-tls-atexit-lib.so", RTLD_LAZY); + if (!handle) + { + printf ("Unable to load DSO: %s\n", dlerror ()); + return (void *) (uintptr_t) 1; + } + + void (*foo) (void) = (void (*) (void)) dlsym(handle, "do_foo"); + + if (!foo) + { + printf ("Unable to find symbol: %s\n", dlerror ()); + exit (1); + } + + foo (); + + /* This should not unload the DSO. If it does, then the thread exit will + result in a segfault. */ + dlclose (handle); + pthread_mutex_unlock (&m); + + return NULL; +} + +int +main (void) +{ + pthread_t t; + int ret; + void *thr_ret; + + if ((ret = pthread_create (&t, NULL, load, NULL)) != 0) + { + printf ("pthread_create failed: %s\n", strerror (ret)); + return 1; + } + + if ((ret = pthread_join (t, &thr_ret)) != 0) + { + printf ("pthread_create failed: %s\n", strerror (ret)); + return 1; + } + + if (thr_ret != NULL) + return 1; + + /* Now this should unload the DSO. */ + dlclose (handle); + + /* Run through our maps and ensure that the DSO is unloaded. */ + FILE *f = fopen ("/proc/self/maps", "r"); + + if (f == NULL) + { + perror ("Failed to open /proc/self/maps"); + fprintf (stderr, "Skipping verification of DSO unload\n"); + return 0; + } + + char *line = NULL; + size_t s = 0; + while (getline (&line, &s, f) > 0) + { + if (strstr (line, "tst-tls-atexit-lib.so")) + { + printf ("DSO not unloaded yet:\n%s", line); + return 1; + } + } + free (line); + + return 0; +} -- cgit 1.4.1