Bug 20915: Do not initialize DTV of other threads.

In _dl_nothread_init_static_tls() and init_one_static_tls() we must not
touch the DTV of other threads since we do not have ownership of them.
The DTV need not be initialized at this point anyway since only LD/GD
accesses will use them. If LD/GD accesses occur they will take care to
initialize their own thread's DTV.

Concurrency comments were removed from the patch since they need to be
reworked along with a full description of DTV ownership and when it is
or is not safe to modify these structures.

Alexandre Oliva's original patch and discussion:
https://sourceware.org/ml/libc-alpha/2016-09/msg00512.html

diff --git a/ChangeLog b/ChangeLog
index f70871d4eca2a66f05da209873ced66ac7f3eadf..9ed7ff6883ce219109c4facdfc5e7b4acc78e253 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2017-02-03  Alexandre Oliva  <aoliva@redhat.com>
+           Florian Weimer  <fweimer@redhat.com>
+           Carlos O'Donell  <carlos@redhat.com>
+
+       [BZ #20915]
+       * elf/dl-reloc.c (_dl_nothread_init_static_tls):
+       Do not initialize DTV.
+       * nptl/allocatestack.c (init_one_static_tls): Likewise.
+
 2017-02-03  David S. Miller  <davem@davemloft.net>
 
        * sysdeps/sparc/sparc64/fpu/multiarch/s_fmax-vis3.S: Remove file.

diff --git a/elf/dl-reloc.c b/elf/dl-reloc.c
index 52311f0278695c606b7831b61d3b7cabf06f780d..4ac558df525ffc7c38e290df0c209e36eb265029 100644 (file)
--- a/elf/dl-reloc.c
+++ b/elf/dl-reloc.c
@@ -137,12 +137,6 @@ _dl_nothread_init_static_tls (struct link_map *map)
 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 #endif
 
-  /* Fill in the DTV slot so that a later LD/GD access will find it.  */
-  dtv_t *dtv = THREAD_DTV ();
-  assert (map->l_tls_modid <= dtv[-1].counter);
-  dtv[map->l_tls_modid].pointer.to_free = NULL;
-  dtv[map->l_tls_modid].pointer.val = dest;
-
   /* Initialize the memory.  */
   memset (__mempcpy (dest, map->l_tls_initimage, map->l_tls_initimage_size),
          '\0', map->l_tls_blocksize - map->l_tls_initimage_size);

diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index 6402ea43f28bd0de383bac72129deac4130077a7..8a228ab25427e5eba37c05a012792dd40829858b 100644 (file)
--- a/nptl/allocatestack.c
+++ b/nptl/allocatestack.c
@@ -1191,11 +1191,6 @@ init_one_static_tls (struct pthread *curp, struct link_map *map)
 #  error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 # endif
 
-  /* Fill in the DTV slot so that a later LD/GD access will find it.  */
-  dtv_t *dtv = GET_DTV (TLS_TPADJ (curp));
-  dtv[map->l_tls_modid].pointer.to_free = NULL;
-  dtv[map->l_tls_modid].pointer.val = dest;
-
   /* Initialize the memory.  */
   memset (__mempcpy (dest, map->l_tls_initimage, map->l_tls_initimage_size),
          '\0', map->l_tls_blocksize - map->l_tls_initimage_size);