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Re: [PATCH] BZ #14545: Always check dtv before freeing dtv[-1]


On Thu, Sep 6, 2012 at 12:43 PM, Roland McGrath <roland@hack.frob.com> wrote:
>> diff --git a/csu/libc-tls.c b/csu/libc-tls.c
>> index b00a5cc..eb9c502 100644
>> --- a/csu/libc-tls.c
>> +++ b/csu/libc-tls.c
>> @@ -65,6 +65,8 @@ size_t _dl_tls_static_size = 2048;
>>  size_t _dl_tls_static_used;
>>  /* Alignment requirement of the static TLS block.  */
>>  size_t _dl_tls_static_align;
>> +/* Initial dtv of the main thread, not allocated with normal malloc.  */
>> +void *_dl_initial_dtv = &static_dtv[1];
>
> Make this 'void *const' so it stays in .rodata.
>
> Better yet, make static_dtv a global _dl_static_dtv and put:
>
> #ifndef SHARED
> # define _dl_initial_dtv ((void *) &_dl_static_dtv[1])
> #endif
>
> into ldsodefs.h so we don't waste a data word on this at all.
>

I am testing this patch on x86-64.  OK to install if there is
no regression?

Thanks.

-- 
H.J.
---
2012-09-06  H.J. Lu  <hongjiu.lu@intel.com>

	* csu/libc-tls.c (static_dtv): Renamed to ...
	(_dl_static_dtv): This.  Make it global.
	(_dl_initial_dtv): Removed.
	(__libc_setup_tls): Updated.
	* elf/dl-tls.c (DL_INITIAL_DTV): New macro.
	(_dl_deallocate_tls): Replace GL(dl_initial_dtv) with
	DL_INITIAL_DTV.

diff --git a/csu/libc-tls.c b/csu/libc-tls.c
index eb9c502..9bc4d84 100644
--- a/csu/libc-tls.c
+++ b/csu/libc-tls.c
@@ -32,7 +32,7 @@ extern ElfW(Phdr) *_dl_phdr;
 extern size_t _dl_phnum;


-static dtv_t static_dtv[2 + TLS_SLOTINFO_SURPLUS];
+dtv_t _dl_static_dtv[2 + TLS_SLOTINFO_SURPLUS];


 static struct
@@ -65,8 +65,6 @@ size_t _dl_tls_static_size = 2048;
 size_t _dl_tls_static_used;
 /* Alignment requirement of the static TLS block.  */
 size_t _dl_tls_static_align;
-/* Initial dtv of the main thread, not allocated with normal malloc.  */
-void *_dl_initial_dtv = &static_dtv[1];

 /* Generation counter for the dtv.  */
 size_t _dl_tls_generation;
@@ -165,33 +163,33 @@ __libc_setup_tls (size_t tcbsize, size_t tcbalign)
 		       & ~(max_align - 1));

   /* Initialize the dtv.  [0] is the length, [1] the generation counter.  */
-  static_dtv[0].counter = (sizeof (static_dtv) / sizeof (static_dtv[0])) - 2;
-  // static_dtv[1].counter = 0;		would be needed if not already done
+  _dl_static_dtv[0].counter = (sizeof (_dl_static_dtv) / sizeof
(_dl_static_dtv[0])) - 2;
+  // _dl_static_dtv[1].counter = 0;		would be needed if not already done

   /* Initialize the TLS block.  */
 #if TLS_TCB_AT_TP
-  static_dtv[2].pointer.val = ((char *) tlsblock + tcb_offset
+  _dl_static_dtv[2].pointer.val = ((char *) tlsblock + tcb_offset
 			       - roundup (memsz, align ?: 1));
   static_map.l_tls_offset = roundup (memsz, align ?: 1);
 #elif TLS_DTV_AT_TP
-  static_dtv[2].pointer.val = (char *) tlsblock + tcb_offset;
+  _dl_static_dtv[2].pointer.val = (char *) tlsblock + tcb_offset;
   static_map.l_tls_offset = tcb_offset;
 #else
 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 #endif
-  static_dtv[2].pointer.is_static = true;
+  _dl_static_dtv[2].pointer.is_static = true;
   /* sbrk gives us zero'd memory, so we don't need to clear the remainder.  */
-  memcpy (static_dtv[2].pointer.val, initimage, filesz);
+  memcpy (_dl_static_dtv[2].pointer.val, initimage, filesz);

   /* Install the pointer to the dtv.  */

   /* Initialize the thread pointer.  */
 #if TLS_TCB_AT_TP
-  INSTALL_DTV ((char *) tlsblock + tcb_offset, static_dtv);
+  INSTALL_DTV ((char *) tlsblock + tcb_offset, _dl_static_dtv);

   const char *lossage = TLS_INIT_TP ((char *) tlsblock + tcb_offset, 0);
 #elif TLS_DTV_AT_TP
-  INSTALL_DTV (tlsblock, static_dtv);
+  INSTALL_DTV (tlsblock, _dl_static_dtv);
   const char *lossage = TLS_INIT_TP (tlsblock, 0);
 #else
 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
diff --git a/elf/dl-tls.c b/elf/dl-tls.c
index ff59e9e..9d896b7 100644
--- a/elf/dl-tls.c
+++ b/elf/dl-tls.c
@@ -464,6 +464,13 @@ _dl_allocate_tls (void *mem)
 rtld_hidden_def (_dl_allocate_tls)


+#ifndef SHARED
+extern dtv_t _dl_static_dtv[];
+# define DL_INITIAL_DTV	(&_dl_static_dtv[1])
+#else
+# define DL_INITIAL_DTV	GL(dl_initial_dtv)
+#endif
+
 void
 internal_function
 _dl_deallocate_tls (void *tcb, bool dealloc_tcb)
@@ -477,7 +484,7 @@ _dl_deallocate_tls (void *tcb, bool dealloc_tcb)
       free (dtv[1 + cnt].pointer.val);

   /* The array starts with dtv[-1].  */
-  if (dtv != GL(dl_initial_dtv))
+  if (dtv != DL_INITIAL_DTV)
     free (dtv - 1);

   if (dealloc_tcb)


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