Re: [PATCH v3 23/37] nptl: Move part of TCB initialization from libpthread to __tls_init_tp

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 16/03/2021 14:30, Florian Weimer via Libc-alpha wrote:
> This initalization should only happen once for the main thread's TCB.
> At present, auditors can achieve this by not linking against
> libpthread.  If libpthread becomes part of libc, doing this
> initialization in libc would happen for every audit namespace,
> or too late (if it happens from the main libc only).  That's why
> moving this code into ld.so seems the right thing to do, right after
> the TCB initialization.

Make sense.

> 
> For !__ASSUME_SET_ROBUST_LIST ports, this also moves the symbol
> __set_robust_list_avail into ld.so, as __nptl_set_robust_list_avail.
> It also turned into a proper boolean flag.
> 
> Inline the __pthread_initialize_pids function because it seems no
> longer useful as a separate function.

LGTM, with just a suggestion below.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>   nptl/Versions                          |  6 +++++
>   nptl/nptl-init.c                       | 36 ++-----------------------
>   nptl/pthread-pids.h                    | 29 --------------------
>   nptl/pthreadP.h                        |  6 +++--
>   nptl/pthread_create.c                  |  4 +--
>   nptl/pthread_mutex_init.c              |  2 +-
>   sysdeps/nptl/dl-tls_init_tp.c          | 37 ++++++++++++++++++++++++++
>   sysdeps/unix/sysv/linux/pthread-pids.h | 29 --------------------
>   8 files changed, 52 insertions(+), 97 deletions(-)
>   delete mode 100644 nptl/pthread-pids.h
>   delete mode 100644 sysdeps/unix/sysv/linux/pthread-pids.h
> 
> diff --git a/nptl/Versions b/nptl/Versions
> index b619df41fb..c50a5442af 100644
> --- a/nptl/Versions
> +++ b/nptl/Versions
> @@ -417,3 +417,9 @@ libpthread {
>       __pthread_initialize_minimal;
>     }
>   }
> +
> +ld {
> +  GLIBC_PRIVATE {
> +     __nptl_set_robust_list_avail;
> +  }
> +}
> \ No newline at end of file

Ok.

> diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
> index de64e34783..5913bf7272 100644
> --- a/nptl/nptl-init.c
> +++ b/nptl/nptl-init.c
> @@ -36,7 +36,6 @@
>   #include <futex-internal.h>
>   #include <kernel-features.h>
>   #include <libc-pointer-arith.h>
> -#include <pthread-pids.h>
>   #include <pthread_mutex_conf.h>
>   
>   #ifndef TLS_MULTIPLE_THREADS_IN_TCB
> @@ -48,15 +47,6 @@ int *__libc_multiple_threads_ptr attribute_hidden;
>   size_t __static_tls_size;
>   size_t __static_tls_align_m1;
>   
> -#ifndef __ASSUME_SET_ROBUST_LIST
> -/* Negative if we do not have the system call and we can use it.  */
> -int __set_robust_list_avail;
> -# define set_robust_list_not_avail() \
> -  __set_robust_list_avail = -1
> -#else
> -# define set_robust_list_not_avail() do { } while (0)
> -#endif
> -
>   /* Version of the library, used in libthread_db to detect mismatches.  */
>   static const char nptl_version[] __attribute_used__ = VERSION;
>   
> @@ -194,31 +184,9 @@ static bool __nptl_initial_report_events __attribute_used__;
>   void
>   __pthread_initialize_minimal_internal (void)
>   {
> -  /* Minimal initialization of the thread descriptor.  */
> +  /* Partial initialization of the TCB already happened in TLS_INIT_TP
> +     and __tls_init_tp.  */
>     struct pthread *pd = THREAD_SELF;
> -  __pthread_initialize_pids (pd);
> -  THREAD_SETMEM (pd, specific[0], &pd->specific_1stblock[0]);
> -  THREAD_SETMEM (pd, user_stack, true);
> -
> -  /* Initialize the robust mutex data.  */
> -  {
> -#if __PTHREAD_MUTEX_HAVE_PREV
> -    pd->robust_prev = &pd->robust_head;
> -#endif
> -    pd->robust_head.list = &pd->robust_head;
> -    pd->robust_head.futex_offset = (offsetof (pthread_mutex_t, __data.__lock)
> -				    - offsetof (pthread_mutex_t,
> -						__data.__list.__next));
> -    int res = INTERNAL_SYSCALL_CALL (set_robust_list, &pd->robust_head,
> -				     sizeof (struct robust_list_head));
> -    if (INTERNAL_SYSCALL_ERROR_P (res))
> -      set_robust_list_not_avail ();
> -  }
> -
> -  /* Set initial thread's stack block from 0 up to __libc_stack_end.
> -     It will be bigger than it actually is, but for unwind.c/pt-longjmp.c
> -     purposes this is good enough.  */
> -  THREAD_SETMEM (pd, stackblock_size, (size_t) __libc_stack_end);
>   
>     /* Before initializing GL (dl_stack_user), the debugger could not
>        find us and had to set __nptl_initial_report_events.  Propagate

Ok.

> diff --git a/nptl/pthread-pids.h b/nptl/pthread-pids.h
> deleted file mode 100644
> index 1a0e9ade41..0000000000
> --- a/nptl/pthread-pids.h
> +++ /dev/null
> @@ -1,29 +0,0 @@
> -/* Initialize pid and tid fields of struct pthread.  Stub version.
> -   Copyright (C) 2015-2021 Free Software Foundation, Inc.
> -   This file is part of the GNU C Library.
> -
> -   The GNU C Library is free software; you can redistribute it and/or
> -   modify it under the terms of the GNU Lesser General Public
> -   License as published by the Free Software Foundation; either
> -   version 2.1 of the License, or (at your option) any later version.
> -
> -   The GNU C Library is distributed in the hope that it will be useful,
> -   but WITHOUT ANY WARRANTY; without even the implied warranty of
> -   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> -   Lesser General Public License for more details.
> -
> -   You should have received a copy of the GNU Lesser General Public
> -   License along with the GNU C Library; if not, see
> -   <https://www.gnu.org/licenses/>.  */
> -
> -#include <pthreadP.h>
> -
> -/* Initialize PD->pid and PD->tid for the initial thread.  If there is
> -   setup required to arrange that __exit_thread causes PD->tid to be
> -   cleared and futex-woken, then this function should do that as well.  */
> -static inline void
> -__pthread_initialize_pids (struct pthread *pd)
> -{
> -#error "sysdeps pthread-pids.h file required"
> -  pd->pid = pd->tid = -1;
> -}

Ok.

> diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
> index 4b486b3577..68f8ef5aa1 100644
> --- a/nptl/pthreadP.h
> +++ b/nptl/pthreadP.h
> @@ -224,8 +224,10 @@ extern unsigned int __nptl_nthreads;
>   libc_hidden_proto (__nptl_nthreads)
>   
>   #ifndef __ASSUME_SET_ROBUST_LIST
> -/* Negative if we do not have the system call and we can use it.  */
> -extern int __set_robust_list_avail attribute_hidden;
> +/* True if the set_robust_list system call works.  Initialized in
> +   __tls_init_tp.  */
> +extern bool __nptl_set_robust_list_avail;
> +rtld_hidden_proto (__nptl_set_robust_list_avail)
>   #endif
>   
>   /* Thread Priority Protection.  */

Now that you are touching it, maybe it would be better to move the
__ASSUME_SET_ROBUST_LIST handling only to the dl-tls_init_tp.c and
always define __nptl_set_robust_list_avail (at least one initialization
case)?

> diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
> index 58e10e7741..51340acc4d 100644
> --- a/nptl/pthread_create.c
> +++ b/nptl/pthread_create.c
> @@ -289,7 +289,7 @@ START_THREAD_DEFN
>     __ctype_init ();
>   
>   #ifndef __ASSUME_SET_ROBUST_LIST
> -  if (__set_robust_list_avail >= 0)
> +  if (__nptl_set_robust_list_avail)
>   #endif
>       {
>         /* This call should never fail because the initial call in init.c
> @@ -439,7 +439,7 @@ START_THREAD_DEFN
>     /* We let the kernel do the notification if it is able to do so.
>        If we have to do it here there for sure are no PI mutexes involved
>        since the kernel support for them is even more recent.  */
> -  if (__set_robust_list_avail < 0
> +  if (!__nptl_set_robust_list_avail
>         && __builtin_expect (robust != (void *) &pd->robust_head, 0))
>       {
>         do

Ok.

> diff --git a/nptl/pthread_mutex_init.c b/nptl/pthread_mutex_init.c
> index 233cebc504..f5c3a4b464 100644
> --- a/nptl/pthread_mutex_init.c
> +++ b/nptl/pthread_mutex_init.c
> @@ -95,7 +95,7 @@ __pthread_mutex_init (pthread_mutex_t *mutex,
>       {
>   #ifndef __ASSUME_SET_ROBUST_LIST
>         if ((imutexattr->mutexkind & PTHREAD_MUTEXATTR_FLAG_PSHARED) != 0
> -	  && __set_robust_list_avail < 0)
> +	  && !__nptl_set_robust_list_avail)
>   	return ENOTSUP;
>   #endif
>   

Ok.

> diff --git a/sysdeps/nptl/dl-tls_init_tp.c b/sysdeps/nptl/dl-tls_init_tp.c
> index 8983808233..c5172b7613 100644
> --- a/sysdeps/nptl/dl-tls_init_tp.c
> +++ b/sysdeps/nptl/dl-tls_init_tp.c
> @@ -16,10 +16,17 @@
>      License along with the GNU C Library; if not, see
>      <https://www.gnu.org/licenses/>.  */
>   
> +#include <kernel-features.h>
>   #include <ldsodefs.h>
>   #include <list.h>
> +#include <nptl/pthreadP.h>
>   #include <tls.h>
>   
> +#ifndef __ASSUME_SET_ROBUST_LIST
> +bool __nptl_set_robust_list_avail;
> +rtld_hidden_data_def (__nptl_set_robust_list_avail)
> +#endif
> +
>   void
>   __tls_init_tp (void)
>   {
> @@ -27,4 +34,34 @@ __tls_init_tp (void)
>     INIT_LIST_HEAD (&GL (dl_stack_used));
>     INIT_LIST_HEAD (&GL (dl_stack_user));
>     list_add (&THREAD_SELF->list, &GL (dl_stack_user));
> +
> +   /* Early initialization of the TCB.   */
> +   struct pthread *pd = THREAD_SELF;
> +   pd->tid = INTERNAL_SYSCALL_CALL (set_tid_address, &pd->tid);
> +   THREAD_SETMEM (pd, specific[0], &pd->specific_1stblock[0]);
> +   THREAD_SETMEM (pd, user_stack, true);
> +
> +  /* Initialize the robust mutex data.  */
> +  {
> +#if __PTHREAD_MUTEX_HAVE_PREV
> +    pd->robust_prev = &pd->robust_head;
> +#endif
> +    pd->robust_head.list = &pd->robust_head;
> +    pd->robust_head.futex_offset = (offsetof (pthread_mutex_t, __data.__lock)
> +                                    - offsetof (pthread_mutex_t,
> +                                                __data.__list.__next));
> +    int res = INTERNAL_SYSCALL_CALL (set_robust_list, &pd->robust_head,
> +                                     sizeof (struct robust_list_head));
> +    if (!INTERNAL_SYSCALL_ERROR_P (res))
> +      {
> +#ifndef __ASSUME_SET_ROBUST_LIST
> +        __nptl_set_robust_list_avail = true;
> +#endif
> +      }
> +  }
> +
> +  /* Set initial thread's stack block from 0 up to __libc_stack_end.
> +     It will be bigger than it actually is, but for unwind.c/pt-longjmp.c
> +     purposes this is good enough.  */
> +  THREAD_SETMEM (pd, stackblock_size, (size_t) __libc_stack_end);
>   }

Ok.

> diff --git a/sysdeps/unix/sysv/linux/pthread-pids.h b/sysdeps/unix/sysv/linux/pthread-pids.h
> deleted file mode 100644
> index 10b58899f5..0000000000
> --- a/sysdeps/unix/sysv/linux/pthread-pids.h
> +++ /dev/null
> @@ -1,29 +0,0 @@
> -/* Initialize pid and tid fields of struct pthread.  Linux version.
> -   Copyright (C) 2015-2021 Free Software Foundation, Inc.
> -   This file is part of the GNU C Library.
> -
> -   The GNU C Library is free software; you can redistribute it and/or
> -   modify it under the terms of the GNU Lesser General Public
> -   License as published by the Free Software Foundation; either
> -   version 2.1 of the License, or (at your option) any later version.
> -
> -   The GNU C Library is distributed in the hope that it will be useful,
> -   but WITHOUT ANY WARRANTY; without even the implied warranty of
> -   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> -   Lesser General Public License for more details.
> -
> -   You should have received a copy of the GNU Lesser General Public
> -   License along with the GNU C Library; if not, see
> -   <https://www.gnu.org/licenses/>.  */
> -
> -#include <pthreadP.h>
> -#include <sysdep.h>
> -
> -/* Initialize PD->pid and PD->tid for the initial thread.  If there is
> -   setup required to arrange that __exit_thread causes PD->tid to be
> -   cleared and futex-woken, then this function should do that as well.  */
> -static inline void
> -__pthread_initialize_pids (struct pthread *pd)
> -{
> -  pd->tid = INTERNAL_SYSCALL_CALL (set_tid_address, &pd->tid);
> -}
> 

Ok.