Re: [PATCH] elf, nptl: Initialize static TLS directly in ld.so

["H.J. Lu" <hjl.tools@gmail.com>]

On Tue, May 4, 2021 at 12:01 PM Florian Weimer via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> The stack list is available in ld.so since commit
> 1daccf403b1bd86370eb94edca794dc106d02039 ("nptl: Move stack list
> variables into _rtld_global"), so it's possible to walk the stack
> list directly in ld.so and perform the initialization there.
>
> This eliminates an unprotected function pointer from _rtld_global
> and reduces the libpthread initialization code.
>
> ---
>  elf/dl-open.c              |  2 +-
>  elf/dl-reloc.c             |  5 +++--
>  elf/dl-support.c           |  3 +--
>  elf/dl-tls.c               | 39 +++++++++++++++++++++++++++++++++++++++
>  elf/rtld.c                 |  2 ++
>  nptl/allocatestack.c       | 35 -----------------------------------
>  nptl/nptl-init.c           |  2 --
>  nptl/pthreadP.h            |  2 --
>  sysdeps/generic/ldsodefs.h | 19 +++++++++++++++++++
>  9 files changed, 65 insertions(+), 44 deletions(-)
>
> diff --git a/elf/dl-open.c b/elf/dl-open.c
> index ab7aaa345e..09f0df7d38 100644
> --- a/elf/dl-open.c
> +++ b/elf/dl-open.c
> @@ -426,7 +426,7 @@ TLS generation counter wrapped!  Please report this."));
>           _dl_update_slotinfo (imap->l_tls_modid);
>  #endif
>
> -         GL(dl_init_static_tls) (imap);
> +         dl_init_static_tls (imap);
>           assert (imap->l_need_tls_init == 0);
>         }
>      }
> diff --git a/elf/dl-reloc.c b/elf/dl-reloc.c
> index c2df26deea..bb9ca1a101 100644
> --- a/elf/dl-reloc.c
> +++ b/elf/dl-reloc.c
> @@ -118,7 +118,7 @@ _dl_try_allocate_static_tls (struct link_map *map, bool optional)
>         (void) _dl_update_slotinfo (map->l_tls_modid);
>  #endif
>
> -      GL(dl_init_static_tls) (map);
> +      dl_init_static_tls (map);
>      }
>    else
>      map->l_need_tls_init = 1;
> @@ -141,6 +141,7 @@ cannot allocate memory in static TLS block"));
>      }
>  }
>
> +#if !THREAD_GSCOPE_IN_TCB
>  /* Initialize static TLS area and DTV for current (only) thread.
>     libpthread implementations should provide their own hook
>     to handle all threads.  */
> @@ -159,7 +160,7 @@ _dl_nothread_init_static_tls (struct link_map *map)
>    memset (__mempcpy (dest, map->l_tls_initimage, map->l_tls_initimage_size),
>           '\0', map->l_tls_blocksize - map->l_tls_initimage_size);
>  }
> -
> +#endif /* !THREAD_GSCOPE_IN_TCB */
>
>  void
>  _dl_relocate_object (struct link_map *l, struct r_scope_elem *scope[],
> diff --git a/elf/dl-support.c b/elf/dl-support.c
> index 7fc2ee78e2..f966a2e7cd 100644
> --- a/elf/dl-support.c
> +++ b/elf/dl-support.c
> @@ -138,8 +138,6 @@ void *_dl_random;
>  #include <dl-procruntime.c>
>  #include <dl-procinfo.c>
>
> -void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;
> -
>  size_t _dl_pagesize = EXEC_PAGESIZE;
>
>  size_t _dl_minsigstacksize = CONSTANT_MINSIGSTKSZ;
> @@ -197,6 +195,7 @@ list_t _dl_stack_user;
>  int _dl_stack_cache_lock;
>  #else
>  int _dl_thread_gscope_count;
> +void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;
>  #endif
>  struct dl_scope_free_list *_dl_scope_free_list;
>
> diff --git a/elf/dl-tls.c b/elf/dl-tls.c
> index f8b32b3ecb..6baff0c1ea 100644
> --- a/elf/dl-tls.c
> +++ b/elf/dl-tls.c
> @@ -29,6 +29,10 @@
>  #include <dl-tls.h>
>  #include <ldsodefs.h>
>
> +#if THREAD_GSCOPE_IN_TCB
> +# include <list.h>
> +#endif
> +
>  #define TUNABLE_NAMESPACE rtld
>  #include <dl-tunables.h>
>
> @@ -1005,3 +1009,38 @@ cannot create TLS data structures"));
>        listp->slotinfo[idx].gen = GL(dl_tls_generation) + 1;
>      }
>  }
> +
> +#if THREAD_GSCOPE_IN_TCB
> +static inline void __attribute__((always_inline))
> +init_one_static_tls (struct pthread *curp, struct link_map *map)
> +{
> +# if TLS_TCB_AT_TP
> +  void *dest = (char *) curp - map->l_tls_offset;
> +# elif TLS_DTV_AT_TP
> +  void *dest = (char *) curp + map->l_tls_offset + TLS_PRE_TCB_SIZE;
> +# else
> +#  error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
> +# endif
> +
> +  /* 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);
> +}
> +
> +void
> +_dl_init_static_tls (struct link_map *map)
> +{
> +  lll_lock (GL (dl_stack_cache_lock), LLL_PRIVATE);
> +
> +  /* Iterate over the list with system-allocated threads first.  */
> +  list_t *runp;
> +  list_for_each (runp, &GL (dl_stack_used))
> +    init_one_static_tls (list_entry (runp, struct pthread, list), map);
> +
> +  /* Now the list with threads using user-allocated stacks.  */
> +  list_for_each (runp, &GL (dl_stack_user))
> +    init_one_static_tls (list_entry (runp, struct pthread, list), map);
> +
> +  lll_unlock (GL (dl_stack_cache_lock), LLL_PRIVATE);
> +}
> +#endif /* THREAD_GSCOPE_IN_TCB */
> diff --git a/elf/rtld.c b/elf/rtld.c
> index 34879016ad..ad325d4c10 100644
> --- a/elf/rtld.c
> +++ b/elf/rtld.c
> @@ -1139,7 +1139,9 @@ dl_main (const ElfW(Phdr) *phdr,
>    struct dl_main_state state;
>    dl_main_state_init (&state);
>
> +#if !THREAD_GSCOPE_IN_TCB
>    GL(dl_init_static_tls) = &_dl_nothread_init_static_tls;
> +#endif
>
>  #if defined SHARED && defined _LIBC_REENTRANT \
>      && defined __rtld_lock_default_lock_recursive
> diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
> index f1270c3109..8aaba088b1 100644
> --- a/nptl/allocatestack.c
> +++ b/nptl/allocatestack.c
> @@ -951,38 +951,3 @@ __reclaim_stacks (void)
>    GL (dl_stack_cache_lock) = LLL_LOCK_INITIALIZER;
>    __default_pthread_attr_lock = LLL_LOCK_INITIALIZER;
>  }
> -
> -
> -static inline void __attribute__((always_inline))
> -init_one_static_tls (struct pthread *curp, struct link_map *map)
> -{
> -# if TLS_TCB_AT_TP
> -  void *dest = (char *) curp - map->l_tls_offset;
> -# elif TLS_DTV_AT_TP
> -  void *dest = (char *) curp + map->l_tls_offset + TLS_PRE_TCB_SIZE;
> -# else
> -#  error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
> -# endif
> -
> -  /* 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);
> -}
> -
> -void
> -attribute_hidden
> -__pthread_init_static_tls (struct link_map *map)
> -{
> -  lll_lock (GL (dl_stack_cache_lock), LLL_PRIVATE);
> -
> -  /* Iterate over the list with system-allocated threads first.  */
> -  list_t *runp;
> -  list_for_each (runp, &GL (dl_stack_used))
> -    init_one_static_tls (list_entry (runp, struct pthread, list), map);
> -
> -  /* Now the list with threads using user-allocated stacks.  */
> -  list_for_each (runp, &GL (dl_stack_user))
> -    init_one_static_tls (list_entry (runp, struct pthread, list), map);
> -
> -  lll_unlock (GL (dl_stack_cache_lock), LLL_PRIVATE);
> -}
> diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
> index b0879bd87e..fcab5a0904 100644
> --- a/nptl/nptl-init.c
> +++ b/nptl/nptl-init.c
> @@ -191,8 +191,6 @@ __pthread_initialize_minimal_internal (void)
>    GL(dl_make_stack_executable_hook) = &__make_stacks_executable;
>  #endif
>
> -  GL(dl_init_static_tls) = &__pthread_init_static_tls;
> -
>    /* Register the fork generation counter with the libc.  */
>  #ifndef TLS_MULTIPLE_THREADS_IN_TCB
>    __libc_multiple_threads_ptr =
> diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
> index 00d2cfe764..0ce63672c4 100644
> --- a/nptl/pthreadP.h
> +++ b/nptl/pthreadP.h
> @@ -381,8 +381,6 @@ extern int __pthread_multiple_threads attribute_hidden;
>  extern int *__libc_multiple_threads_ptr attribute_hidden;
>  #endif
>
> -extern void __pthread_init_static_tls (struct link_map *) attribute_hidden;
> -
>  extern size_t __pthread_get_minstack (const pthread_attr_t *attr);
>
>  /* Namespace save aliases.  */
> diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
> index 67c6686015..1b064c5894 100644
> --- a/sysdeps/generic/ldsodefs.h
> +++ b/sysdeps/generic/ldsodefs.h
> @@ -464,7 +464,9 @@ struct rtld_global
>    /* Generation counter for the dtv.  */
>    EXTERN size_t _dl_tls_generation;
>
> +#if !THREAD_GSCOPE_IN_TCB
>    EXTERN void (*_dl_init_static_tls) (struct link_map *);
> +#endif
>
>    /* Scopes to free after next THREAD_GSCOPE_WAIT ().  */
>    EXTERN struct dl_scope_free_list
> @@ -1270,6 +1272,23 @@ extern void _dl_non_dynamic_init (void)
>  extern void _dl_aux_init (ElfW(auxv_t) *av)
>       attribute_hidden;
>
> +/* Initialize the static TLS space for the link map in all existing
> +   threads. */
> +#if THREAD_GSCOPE_IN_TCB
> +void _dl_init_static_tls (struct link_map *map) attribute_hidden;
> +#endif
> +static inline void
> +dl_init_static_tls (struct link_map *map)
> +{
> +#if THREAD_GSCOPE_IN_TCB
> +  /* The stack list is available to ld.so, so the initialization can
> +     be handled within ld.so directly.  */
> +  _dl_init_static_tls (map);
> +#else
> +  GL (dl_init_static_tls) (map);
> +#endif
> +}
> +
>  /* Return true if the ld.so copy in this namespace is actually active
>     and working.  If false, the dl_open/dlfcn hooks have to be used to
>     call into the outer dynamic linker (which happens after static
>

LGTM.

Thanks.

-- 
H.J.