glibc/misc/sbrk.c

/* Copyright (C) 1991-2020 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 <errno.h>
#include <stdint.h>
#include <unistd.h>
#include <libc-internal.h>

/* Defined in brk.c.  */
extern void *__curbrk;
extern int __brk (void *addr);

/* Extend the process's data space by INCREMENT.
   If INCREMENT is negative, shrink data space by - INCREMENT.
   Return start of new space allocated, or -1 for errors.  */
void *
__sbrk (intptr_t increment)
{
  void *oldbrk;

  /* If this is not part of the dynamic library or the library is used
     via dynamic loading in a statically linked program update
     __curbrk from the kernel's brk value.  That way two separate
     instances of __brk and __sbrk can share the heap, returning
     interleaved pieces of it.  */
  if (__curbrk == NULL || __libc_multiple_libcs)
    if (__brk (0) < 0)		/* Initialize the break.  */
      return (void *) -1;

  if (increment == 0)
    return __curbrk;

  oldbrk = __curbrk;
  if (increment > 0
      ? ((uintptr_t) oldbrk + (uintptr_t) increment < (uintptr_t) oldbrk)
      : ((uintptr_t) oldbrk < (uintptr_t) -increment))
    {
      __set_errno (ENOMEM);
      return (void *) -1;
    }

  if (__brk (oldbrk + increment) < 0)
    return (void *) -1;

  return oldbrk;
}
libc_hidden_def (__sbrk)
weak_alias (__sbrk, sbrk)