Re: [PATCH v5] Destructor support for C++11 thread_local variables

["Carlos O'Donell" <carlos at redhat dot com>]

On 02/15/2013 06:50 AM, Siddhesh Poyarekar wrote:
> Hi,
> 
> Here's an updated version of the C++11 thread_local destructor
> implementation.  I have made a couple of updates to the patch,
> including those that Carlos suggested in his review.  I found that the
> patch broke checklocalplt since a PLT entry was generated for
> __call_tls_dtors.  I have fixed that now.  Built and regression tested
> on x86_64.

OK to checkin once you get the naming straight.

> +static __thread struct dtor_list *tls_dtor_list;
> +static __thread void *dso_handle_cache;

s/handle/symbol/g

> +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.  */

Explain in the comment that `dso_symbol' is a per-DSO hidden symbol
named `__dso_handle' used to identify the DSO.

> +int
> +__cxa_thread_atexit_impl (dtor_func func, void *obj, void *dso_handle)

s/handle/symbol/g

> +{
> +  /* 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_handle_cache != dso_handle, 0))
> +    {
> +      ElfW(Addr) caller = (ElfW(Addr)) dso_handle;
> +
> +      struct link_map *l = _dl_find_dso_for_object (caller);

Now that we call it a symbol it makes sense to me that we need to
translate the symbol into an actual handle :-)

> +
> +      /* 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;
> +}

Cheers,
Carlos.