sysdeps/unix/sysv/linux/dl-early_allocate.c

   1 /* Early memory allocation for the dynamic loader.  Generic version.
   2    Copyright (C) 2022-2024 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 }