malloc/tst-malloc-alternate-path.c

   1 /* Test that malloc uses mmap when sbrk or brk fails.
   2    Copyright (C) 2024-2025 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 /* This test sets up an obstruction to ensure that brk/sbrk fails to
  20    grow the heap, then verifies that malloc uses mmap for allocations
  21    instead.  */
  22
  23 #include <unistd.h>
  24 #include <sys/mman.h>
  25 #include <stdlib.h>
  26 #include <libc-pointer-arith.h>
  27 #include <support/check.h>
  28 #include <stddef.h>
  29 #include <stdalign.h>
  30
  31 #define LARGE_SIZE (10 * (1 << 20)) // 10 MB
  32 static long page_size;
  33
  34 static int
  35 do_test (void)
  36 {
  37   /* Get current program break.  */
  38   void *current_brk = sbrk (0);
  39
  40   page_size = sysconf (_SC_PAGESIZE);
  41
  42   /* Round up to the next page boundary.  */
  43   void *next_page_boundary = PTR_ALIGN_UP (current_brk, page_size);
  44
  45   /* Place a mapping using mmap at the next page boundary.  */
  46   void *obstruction_addr
  47   = mmap (next_page_boundary, page_size, PROT_READ,
  48     MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
  49
  50   /* Check if memory obstruction is set up correctly.  */
  51   TEST_VERIFY_EXIT (obstruction_addr == next_page_boundary);
  52
  53   /* Try to extend the heap beyond the obstruction using sbrk */
  54   int *ptr = sbrk (page_size);
  55   TEST_VERIFY_EXIT (ptr == (void *) -1);
  56
  57   /* Attempt multiple small allocations using malloc.  */
  58   for (size_t i = 0; i < page_size / alignof (max_align_t); i++)
  59     {
  60       TEST_VERIFY (malloc (alignof (max_align_t)));
  61     }
  62
  63   /* Attempt to allocate a large block of memory using malloc.  */
  64   TEST_VERIFY_EXIT (malloc (LARGE_SIZE) != NULL);
  65
  66   /* Check if malloc changed current program break.  */
  67   TEST_VERIFY_EXIT (current_brk == sbrk (0));
  68
  69   return 0;
  70 }
  71
  72 #include <support/test-driver.c>