1  /* Early memory allocation for the dynamic loader.  Generic version.
       2     Copyright (C) 2022-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library; if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  /* Mark symbols hidden in static PIE for early self relocation to work.  */
      20  #if BUILD_PIE_DEFAULT
      21  # pragma GCC visibility push(hidden)
      22  #endif
      23  #include <startup.h>
      24  
      25  #include <ldsodefs.h>
      26  #include <stddef.h>
      27  #include <string.h>
      28  #include <sysdep.h>
      29  #include <unistd.h>
      30  
      31  #include <brk_call.h>
      32  #include <mmap_call.h>
      33  
      34  /* Defined in brk.c.  */
      35  extern void *__curbrk;
      36  
      37  void *
      38  _dl_early_allocate (size_t size)
      39  {
      40    void *result;
      41  
      42    if (__curbrk != NULL)
      43      /* If the break has been initialized, brk must have run before,
      44         so just call it once more.  */
      45      {
      46        result = __sbrk (size);
      47        if (result == (void *) -1)
      48          result = NULL;
      49      }
      50    else
      51      {
      52        /* If brk has not been invoked, there is no need to update
      53           __curbrk.  The first call to brk will take care of that.  */
      54        void *previous = __brk_call (0);
      55        result = __brk_call (previous + size);
      56        if (result == previous)
      57          result = NULL;
      58        else
      59          result = previous;
      60      }
      61  
      62    /* If brk fails, fall back to mmap.  This can happen due to
      63       unfortunate ASLR layout decisions and kernel bugs, particularly
      64       for static PIE.  */
      65    if (result == NULL)
      66      {
      67        long int ret;
      68        int prot = PROT_READ | PROT_WRITE;
      69        int flags = MAP_PRIVATE | MAP_ANONYMOUS;
      70  #ifdef __NR_mmap2
      71        ret = MMAP_CALL_INTERNAL (mmap2, 0, size, prot, flags, -1, 0);
      72  #else
      73        ret = MMAP_CALL_INTERNAL (mmap, 0, size, prot, flags, -1, 0);
      74  #endif
      75        if (INTERNAL_SYSCALL_ERROR_P (ret))
      76          result = NULL;
      77        else
      78          result = (void *) ret;
      79      }
      80  
      81    return result;
      82  }