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authorAndrew Hunter <ahh@google.com>2014-01-03 11:22:26 -0800
committerPaul Pluzhnikov <ppluzhnikov@google.com>2014-01-03 11:22:26 -0800
commit7f507ee17aee720fa423fa38502bc3caa0dd03d7 (patch)
tree05ec2f0128d719097d18b531bf5e19c617520649 /elf/dl-reloc.c
parent7dd009d8656c0f5c1c633f3764746335a6feefa7 (diff)
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Async-signal safe TLS.
ChangeLog: 2014-01-03 Andrew Hunter <ahh@google.com> * elf/dl-open.c (): New comment. * elf/dl-reloc.c (_dl_try_allocate_static_tls): Use atomic_compare_and_exchange_bool_acq (_dl_allocate_static_tls): Block signals. * elf/dl-tls.c (allocate_and_init): Return void. (_dl_update_slotinfo): Block signals, use atomic update. nptl/ChangeLog: 2014-01-03 Andrew Hunter <ahh@google.com> * nptl/Makefile (tst-tls7): New test. * nptl/tst-tls7.c: New file. * nptl/tst-tls7mod.c: New file. * nptl/allocatestack.c (init_one_static_tls): Use atomic barrier.
Diffstat (limited to 'elf/dl-reloc.c')
-rw-r--r--elf/dl-reloc.c48
1 files changed, 43 insertions, 5 deletions
diff --git a/elf/dl-reloc.c b/elf/dl-reloc.c
index 1f66fccee2..81ee47eb62 100644
--- a/elf/dl-reloc.c
+++ b/elf/dl-reloc.c
@@ -16,8 +16,10 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
+#include <atomic.h>
#include <errno.h>
#include <libintl.h>
+#include <signal.h>
#include <stdlib.h>
#include <unistd.h>
#include <ldsodefs.h>
@@ -70,8 +72,6 @@ _dl_try_allocate_static_tls (struct link_map *map)
size_t offset = GL(dl_tls_static_used) + (freebytes - n * map->l_tls_align
- map->l_tls_firstbyte_offset);
-
- map->l_tls_offset = GL(dl_tls_static_used) = offset;
#elif TLS_DTV_AT_TP
/* dl_tls_static_used includes the TCB at the beginning. */
size_t offset = (((GL(dl_tls_static_used)
@@ -83,7 +83,36 @@ _dl_try_allocate_static_tls (struct link_map *map)
if (used > GL(dl_tls_static_size))
goto fail;
- map->l_tls_offset = offset;
+#else
+# error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
+#endif
+ /* We've computed the new value we want, now try to install it. */
+ ptrdiff_t val;
+ if ((val = map->l_tls_offset) == NO_TLS_OFFSET)
+ {
+ /* l_tls_offset starts out at NO_TLS_OFFSET, and all attempts to
+ change it go from NO_TLS_OFFSET to some other value. We use
+ compare_and_exchange to ensure only one attempt succeeds. We
+ don't actually need any memory ordering here, but _acq is the
+ weakest available. */
+ (void ) atomic_compare_and_exchange_bool_acq (&map->l_tls_offset,
+ offset,
+ NO_TLS_OFFSET);
+ val = map->l_tls_offset;
+ assert (val != NO_TLS_OFFSET);
+ }
+ if (val != offset)
+ {
+ /* We'd like to set a static offset for this section, but another
+ thread has already used a dynamic TLS block for it. Since we can
+ only use static offsets if everyone does (and it's not practical
+ to move that thread's dynamic block), we have to fail. */
+ goto fail;
+ }
+ /* We installed the value; now update the globals. */
+#if TLS_TCB_AT_TP
+ GL(dl_tls_static_used) = offset;
+#elif TLS_DTV_AT_TP
map->l_tls_firstbyte_offset = GL(dl_tls_static_used);
GL(dl_tls_static_used) = used;
#else
@@ -114,8 +143,17 @@ void
internal_function __attribute_noinline__
_dl_allocate_static_tls (struct link_map *map)
{
- if (map->l_tls_offset == FORCED_DYNAMIC_TLS_OFFSET
- || _dl_try_allocate_static_tls (map))
+ /* We wrap this in a signal mask because it has to iterate all threads
+ (including this one) and update this map's TLS entry. A signal handler
+ accessing TLS would try to do the same update and break. */
+ sigset_t old;
+ _dl_mask_all_signals (&old);
+ int err = -1;
+ if (map->l_tls_offset != FORCED_DYNAMIC_TLS_OFFSET)
+ err = _dl_try_allocate_static_tls (map);
+
+ _dl_unmask_signals (&old);
+ if (err != 0)
{
_dl_signal_error (0, map->l_name, NULL, N_("\
cannot allocate memory in static TLS block"));