malloc/tst-free-errno.c

   1 /* Test that free preserves errno.
   2    Copyright (C) 2020-2022 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 #include <errno.h>
  20 #include <stdlib.h>
  21 #include <string.h>
  22 #include <unistd.h>
  23 #include <fcntl.h>
  24 #include <stdint.h>
  25 #include <string.h>
  26 #include <sys/mman.h>
  27 #include <support/check.h>
  28 #include <support/support.h>
  29 #include <support/temp_file.h>
  30 #include <support/xunistd.h>
  31
  32 /* The __attribute__ ((weak)) prevents a GCC optimization.  Without
  33    it, GCC would "know" that errno is unchanged by calling free (ptr),
  34    when ptr was the result of a malloc call in the same function.  */
  35 int __attribute__ ((weak))
  36 get_errno (void)
  37 {
  38   return errno;
  39 }
  40
  41 static int
  42 do_test (void)
  43 {
  44   /* Check that free() preserves errno.  */
  45   {
  46     errno = 1789; /* Liberté, égalité, fraternité.  */
  47     free (NULL);
  48     TEST_VERIFY (get_errno () == 1789);
  49   }
  50   { /* Large memory allocations, to force mmap.  */
  51     enum { N = 2 };
  52     void * volatile ptrs[N];
  53     size_t i;
  54     for (i = 0; i < N; i++)
  55       ptrs[i] = xmalloc (5318153);
  56     for (i = 0; i < N; i++)
  57       {
  58         errno = 1789;
  59         free (ptrs[i]);
  60         TEST_VERIFY (get_errno () == 1789);
  61       }
  62   }
  63
  64   /* Test a less common code path.
  65      When malloc() is based on mmap(), free() can sometimes call munmap().
  66      munmap() usually succeeds, but fails in a particular situation: when
  67        - it has to unmap the middle part of a VMA, and
  68        - the number of VMAs of a process is limited and the limit is
  69          already reached.
  70      The latter condition is fulfilled on Linux, when the file
  71      /proc/sys/vm/max_map_count exists.  For all known Linux versions
  72      the default limit is at most 65536.
  73    */
  74   #if defined __linux__
  75   if (xopen ("/proc/sys/vm/max_map_count", O_RDONLY, 0) >= 0)
  76     {
  77       /* Preparations.  */
  78       size_t pagesize = getpagesize ();
  79       void *firstpage_backup = xmalloc (pagesize);
  80       void *lastpage_backup = xmalloc (pagesize);
  81       /* Allocate a large memory area, as a bumper, so that the MAP_FIXED
  82          allocation later will not overwrite parts of the memory areas
  83          allocated to ld.so or libc.so.  */
  84       xmmap (NULL, 0x1000000, PROT_READ, MAP_ANONYMOUS | MAP_PRIVATE, -1);
  85       /* A file descriptor pointing to a regular file.  */
  86       int fd = create_temp_file ("tst-free-errno", NULL);
  87       if (fd < 0)
  88         FAIL_EXIT1 ("cannot create temporary file");
  89
  90       /* Do a large memory allocation.  */
  91       size_t big_size = 0x1000000;
  92       void * volatile ptr = xmalloc (big_size - 0x100);
  93       char *ptr_aligned = (char *) ((uintptr_t) ptr & ~(pagesize - 1));
  94       /* This large memory allocation allocated a memory area
  95          from ptr_aligned to ptr_aligned + big_size.
  96          Enlarge this memory area by adding a page before and a page
  97          after it.  */
  98       memcpy (firstpage_backup, ptr_aligned, pagesize);
  99       memcpy (lastpage_backup, ptr_aligned + big_size - pagesize,
 100               pagesize);
 101       xmmap (ptr_aligned - pagesize, pagesize + big_size + pagesize,
 102              PROT_READ | PROT_WRITE,
 103              MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1);
 104       memcpy (ptr_aligned, firstpage_backup, pagesize);
 105       memcpy (ptr_aligned + big_size - pagesize, lastpage_backup,
 106               pagesize);
 107
 108       /* Now add as many mappings as we can.
 109          Stop at 65536, in order not to crash the machine (in case the
 110          limit has been increased by the system administrator).  */
 111       for (int i = 0; i < 65536; i++)
 112         if (mmap (NULL, pagesize, PROT_READ, MAP_FILE | MAP_PRIVATE, fd, 0)
 113             == MAP_FAILED)
 114           break;
 115       /* Now the number of VMAs of this process has hopefully attained
 116          its limit.  */
 117
 118       errno = 1789;
 119       /* This call to free() is supposed to call
 120            munmap (ptr_aligned, big_size);
 121          which increases the number of VMAs by 1, which is supposed
 122          to fail.  */
 123       free (ptr);
 124       TEST_VERIFY (get_errno () == 1789);
 125     }
 126   #endif
 127
 128   return 0;
 129 }
 130
 131 #include <support/test-driver.c>