1  /* Copyright (C) 1991-2023 Free Software Foundation, Inc.
       2     This file is part of the GNU C Library.
       3  
       4     The GNU C Library is free software; you can redistribute it and/or
       5     modify it under the terms of the GNU Lesser General Public
       6     License as published by the Free Software Foundation; either
       7     version 2.1 of the License, or (at your option) any later version.
       8  
       9     The GNU C Library is distributed in the hope that it will be useful,
      10     but WITHOUT ANY WARRANTY; without even the implied warranty of
      11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      12     Lesser General Public License for more details.
      13  
      14     You should have received a copy of the GNU Lesser General Public
      15     License along with the GNU C Library; if not, see
      16     <https://www.gnu.org/licenses/>.  */
      17  
      18  /* Mark symbols hidden in static PIE for early self relocation to work.  */
      19  #if BUILD_PIE_DEFAULT
      20  # pragma GCC visibility push(hidden)
      21  #endif
      22  #include <errno.h>
      23  #include <libc-internal.h>
      24  #include <stdbool.h>
      25  #include <stdint.h>
      26  #include <unistd.h>
      27  
      28  /* Defined in brk.c.  */
      29  extern void *__curbrk;
      30  extern int __brk (void *addr);
      31  
      32  /* Extend the process's data space by INCREMENT.
      33     If INCREMENT is negative, shrink data space by - INCREMENT.
      34     Return start of new space allocated, or -1 for errors.  */
      35  void *
      36  __sbrk (intptr_t increment)
      37  {
      38    /* Controls whether __brk (0) is called to read the brk value from
      39       the kernel.  */
      40    bool update_brk = __curbrk == NULL;
      41  
      42  #if defined (SHARED) && ! IS_IN (rtld)
      43    if (!__libc_initial)
      44      {
      45        if (increment != 0)
      46  	{
      47  	  /* Do not allow changing the brk from an inner libc because
      48  	     it cannot be synchronized with the outer libc's brk.  */
      49  	  __set_errno (ENOMEM);
      50  	  return (void *) -1;
      51  	}
      52        /* Querying the kernel's brk value from an inner namespace is
      53  	 fine.  */
      54        update_brk = true;
      55      }
      56  #endif
      57  
      58    if (update_brk)
      59      if (__brk (0) < 0)		/* Initialize the break.  */
      60        return (void *) -1;
      61  
      62    if (increment == 0)
      63      return __curbrk;
      64  
      65    void *oldbrk = __curbrk;
      66    if (increment > 0
      67        ? ((uintptr_t) oldbrk + (uintptr_t) increment < (uintptr_t) oldbrk)
      68        : ((uintptr_t) oldbrk < (uintptr_t) -increment))
      69      {
      70        __set_errno (ENOMEM);
      71        return (void *) -1;
      72      }
      73  
      74    if (__brk (oldbrk + increment) < 0)
      75      return (void *) -1;
      76  
      77    return oldbrk;
      78  }
      79  libc_hidden_def (__sbrk)
      80  weak_alias (__sbrk, sbrk)