[20/26] Linux: set_robust_list syscall number is always available

  Due to the built-in tables, __NR_set_robust_list is always defined
(although it may not be available at run time).
---
 nptl/nptl-init.c      |  4 ----
 nptl/pthread_create.c |  6 ++----
 sysdeps/nptl/fork.c   | 10 ++++------
 3 files changed, 6 insertions(+), 14 deletions(-)
  

On 09/02/2020 17:21, Florian Weimer wrote:
> Due to the built-in tables, __NR_set_robust_list is always defined
> (although it may not be available at run time).

LGTM, thanks. 

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

> ---
>  nptl/nptl-init.c      |  4 ----
>  nptl/pthread_create.c |  6 ++----
>  sysdeps/nptl/fork.c   | 10 ++++------
>  3 files changed, 6 insertions(+), 14 deletions(-)
> 
> diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
> index 1877248014..373be89c95 100644
> --- a/nptl/nptl-init.c
> +++ b/nptl/nptl-init.c
> @@ -129,11 +129,9 @@ static
>  void
>  __nptl_set_robust (struct pthread *self)
>  {
> -#ifdef __NR_set_robust_list
>    INTERNAL_SYSCALL_DECL (err);
>    INTERNAL_SYSCALL (set_robust_list, err, 2, &self->robust_head,
>  		    sizeof (struct robust_list_head));
> -#endif
>  }
>  
>  
> @@ -254,7 +252,6 @@ __pthread_initialize_minimal_internal (void)
>      pd->robust_prev = &pd->robust_head;
>  #endif
>      pd->robust_head.list = &pd->robust_head;
> -#ifdef __NR_set_robust_list
>      pd->robust_head.futex_offset = (offsetof (pthread_mutex_t, __data.__lock)
>  				    - offsetof (pthread_mutex_t,
>  						__data.__list.__next));
> @@ -262,7 +259,6 @@ __pthread_initialize_minimal_internal (void)
>      int res = INTERNAL_SYSCALL (set_robust_list, err, 2, &pd->robust_head,
>  				sizeof (struct robust_list_head));
>      if (INTERNAL_SYSCALL_ERROR_P (res, err))
> -#endif
>        set_robust_list_not_avail ();
>    }
>  

I wonder if it would be better to refactor the __nptl_set_robust to
simplify the '__set_robust_list_avail' handling. Something like:

--
void
__nptl_set_robust (struct pthread *pd)
{
#ifdef __ASSUME_SET_ROBUST_LIST
  static int set_robust_supported = true;
  if (atomic_load_relaxed (&getdents64_supported))
    {
      int res = INTERNAL_SYSCALL_CALL (set_robust_list, &pd->robust_head,
				       sizeof (struct robust_list_head));
      if (INTERNAL_SYSCALL_ERROR_P (res))
	atomic_store_relaxed (&getdents64_supported, false);
    }
#endif
}
--

> diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
> index d3fd58730c..58706b4160 100644
> --- a/nptl/pthread_create.c
> +++ b/nptl/pthread_create.c
> @@ -389,10 +389,9 @@ START_THREAD_DEFN
>    if (__glibc_unlikely (atomic_exchange_acq (&pd->setxid_futex, 0) == -2))
>      futex_wake (&pd->setxid_futex, 1, FUTEX_PRIVATE);
>  
> -#ifdef __NR_set_robust_list
> -# ifndef __ASSUME_SET_ROBUST_LIST
> +#ifndef __ASSUME_SET_ROBUST_LIST
>    if (__set_robust_list_avail >= 0)
> -# endif
> +#endif
>      {
>        INTERNAL_SYSCALL_DECL (err);
>        /* This call should never fail because the initial call in init.c
> @@ -400,7 +399,6 @@ START_THREAD_DEFN
>        INTERNAL_SYSCALL (set_robust_list, err, 2, &pd->robust_head,
>  			sizeof (struct robust_list_head));
>      }
> -#endif
>  
>    /* If the parent was running cancellation handlers while creating
>       the thread the new thread inherited the signal mask.  Reset the

Ok.

> diff --git a/sysdeps/nptl/fork.c b/sysdeps/nptl/fork.c
> index f5cf88d68c..5091a000e3 100644
> --- a/sysdeps/nptl/fork.c
> +++ b/sysdeps/nptl/fork.c
> @@ -83,7 +83,6 @@ __libc_fork (void)
>        if (__fork_generation_pointer != NULL)
>  	*__fork_generation_pointer += __PTHREAD_ONCE_FORK_GEN_INCR;
>  
> -#ifdef __NR_set_robust_list
>        /* Initialize the robust mutex list setting in the kernel which has
>  	 been reset during the fork.  We do not check for errors because if
>  	 it fails here, it must have failed at process startup as well and
> @@ -94,19 +93,18 @@ __libc_fork (void)
>  	 inherit the correct value from the parent.  We do not need to clear
>  	 the pending operation because it must have been zero when fork was
>  	 called.  */
> -# if __PTHREAD_MUTEX_HAVE_PREV
> +#if __PTHREAD_MUTEX_HAVE_PREV
>        self->robust_prev = &self->robust_head;
> -# endif
> +#endif
>        self->robust_head.list = &self->robust_head;
> -# ifdef SHARED
> +#ifdef SHARED
>        if (__builtin_expect (__libc_pthread_functions_init, 0))
>  	PTHFCT_CALL (ptr_set_robust, (self));
> -# else
> +#else
>        extern __typeof (__nptl_set_robust) __nptl_set_robust
>  	__attribute__((weak));
>        if (__builtin_expect (__nptl_set_robust != NULL, 0))
>  	__nptl_set_robust (self);
> -# endif
>  #endif
>  
>        /* Reset the lock state in the multi-threaded case.  */
> 

Ok.