stdlib/test-bz22786: Avoid spurious test failures using alias mappings

On systems without enough random-access memory, stdlib/test-bz22786
will go deeply into swap and time out, even with a substantial
TIMEOUTFACTOR.  This commit adds a facility to construct repeating
strings with alias mappings, so that the requirement for physical
memory, and uses it in stdlib/test-bz22786.

ChangeLog

@@ -1,3 +1,14 @@
+2018-10-30  Florian Weimer  <fweimer@redhat.com>
+
+	Avoid spurious test failures in stdlib/test-bz22786.
+	* support/Makefile (libsupport-routines): Add blob_repeat.
+	(tests): Add tst-support_blob_repeat.
+	* support/blob_repeat.h: New file.
+	* support/blob_repeat.c: Likewise.
+	* support/tst-support_blob_repeat.c: Likewise.
+	* stdlib/test-bz22786.c (do_test): Replace malloc and memset with
+	support_blob_repeat_allocate.
+
 2018-10-30  Andreas Schwab  <schwab@suse.de>
 
 	[BZ #23125]

stdlib/test-bz22786.c

@@ -26,6 +26,7 @@
 #include <unistd.h>
 #include <sys/stat.h>
 #include <sys/types.h>
+#include <support/blob_repeat.h>
 #include <support/check.h>
 #include <support/support.h>
 #include <support/temp_file.h>
@@ -39,17 +40,12 @@ do_test (void)
   const char *lnk = xasprintf ("%s/symlink", dir);
   const size_t path_len = (size_t) INT_MAX + strlen (lnk) + 1;
 
-  DIAG_PUSH_NEEDS_COMMENT;
+  struct support_blob_repeat repeat
-#if __GNUC_PREREQ (7, 0)
+    = support_blob_repeat_allocate ("a", 1, path_len);
-  /* GCC 7 warns about too-large allocations; here we need such
+  char *path = repeat.start;
-     allocation to succeed for the test to work.  */
-  DIAG_IGNORE_NEEDS_COMMENT (7, "-Walloc-size-larger-than=");
-#endif
-  char *path = malloc (path_len);
-  DIAG_POP_NEEDS_COMMENT;
   if (path == NULL)
     {
-      printf ("malloc (%zu): %m\n", path_len);
+      printf ("Repeated allocation (%zu bytes): %m\n", path_len);
       /* On 31-bit s390 the malloc will always fail as we do not have
 	 so much memory, and we want to mark the test unsupported.
 	 Likewise on systems with little physical memory the test will
@@ -62,7 +58,6 @@ do_test (void)
   /* Construct very long path = "/tmp/bz22786.XXXX/symlink/aaaa....."  */
   char *p = mempcpy (path, lnk, strlen (lnk));
   *(p++) = '/';
-  memset (p, 'a', path_len - (p - path) - 2);
   p[path_len - (p - path) - 1] = '\0';
 
   /* This call crashes before the fix for bz22786 on 32-bit platforms.  */
@@ -76,6 +71,7 @@ do_test (void)
 
   /* Cleanup.  */
   unlink (lnk);
+  support_blob_repeat_free (&repeat);
 
   return 0;
 }

support/Makefile

@@ -25,6 +25,7 @@ extra-libs-others = $(extra-libs)
 extra-libs-noinstall := $(extra-libs)
 
 libsupport-routines = \
+  blob_repeat \
   check \
   check_addrinfo \
   check_dns_packet \
@@ -190,6 +191,7 @@ $(objpfx)true-container : $(libsupport)
 tests = \
   README-testing \
   tst-support-namespace \
+  tst-support_blob_repeat \
   tst-support_capture_subprocess \
   tst-support_format_dns_packet \
   tst-support_quote_blob \

support/blob_repeat.c

@@ -0,0 +1,278 @@
+/* Repeating a memory blob, with alias mapping optimization.
+   Copyright (C) 2018 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <support/blob_repeat.h>
+#include <support/check.h>
+#include <support/support.h>
+#include <support/temp_file.h>
+#include <support/xunistd.h>
+#include <sys/mman.h>
+#include <unistd.h>
+#include <wchar.h>
+
+/* Small allocations should use malloc directly instead of the mmap
+   optimization because mappings carry a lot of overhead.  */
+static const size_t maximum_small_size = 4 * 1024 * 1024;
+
+/* Internal helper for fill.  */
+static void
+fill0 (char *target, const char *element, size_t element_size,
+       size_t count)
+{
+  while (count > 0)
+    {
+      memcpy (target, element, element_size);
+      target += element_size;
+      --count;
+    }
+}
+
+/* Fill the buffer at TARGET with COUNT copies of the ELEMENT_SIZE
+   bytes starting at ELEMENT.  */
+static void
+fill (char *target, const char *element, size_t element_size,
+      size_t count)
+{
+  if (element_size == 0 || count == 0)
+    return;
+  else if (element_size == 1)
+    memset (target, element[0], count);
+  else if (element_size == sizeof (wchar_t))
+    {
+      wchar_t wc;
+      memcpy (&wc, element, sizeof (wc));
+      wmemset ((wchar_t *) target, wc, count);
+    }
+  else if (element_size < 1024 && count > 4096)
+    {
+      /* Use larger copies for really small element sizes.  */
+      char buffer[8192];
+      size_t buffer_count = sizeof (buffer) / element_size;
+      fill0 (buffer, element, element_size, buffer_count);
+      while (count > 0)
+        {
+          size_t copy_count = buffer_count;
+          if (copy_count > count)
+            copy_count = count;
+          size_t copy_bytes = copy_count * element_size;
+          memcpy (target, buffer, copy_bytes);
+          target += copy_bytes;
+          count -= copy_count;
+        }
+    }
+  else
+    fill0 (target, element, element_size, count);
+}
+
+/* Use malloc instead of mmap for small allocations and unusual size
+   combinations.  */
+static struct support_blob_repeat
+allocate_malloc (size_t total_size, const void *element, size_t element_size,
+                 size_t count)
+{
+  void *buffer = malloc (total_size);
+  if (buffer == NULL)
+    return (struct support_blob_repeat) { 0 };
+  fill (buffer, element, element_size, count);
+  return (struct support_blob_repeat)
+    {
+      .start = buffer,
+      .size = total_size,
+      .use_malloc = true
+    };
+}
+
+/* Return the least common multiple of PAGE_SIZE and ELEMENT_SIZE,
+   avoiding overflow.  This assumes that PAGE_SIZE is a power of
+   two.  */
+static size_t
+minimum_stride_size (size_t page_size, size_t element_size)
+{
+  TEST_VERIFY_EXIT (page_size > 0);
+  TEST_VERIFY_EXIT (element_size > 0);
+
+  /* Compute the number of trailing zeros common to both sizes.  */
+  unsigned int common_zeros = __builtin_ctzll (page_size | element_size);
+
+  /* In the product, this power of two appears twice, but in the least
+     common multiple, it appears only once.  Therefore, shift one
+     factor.  */
+  size_t multiple;
+  if (__builtin_mul_overflow (page_size >> common_zeros, element_size,
+                              &multiple))
+    return 0;
+  return multiple;
+}
+
+/* Allocations larger than maximum_small_size potentially use mmap
+   with alias mappings.  */
+static struct support_blob_repeat
+allocate_big (size_t total_size, const void *element, size_t element_size,
+              size_t count)
+{
+  unsigned long page_size = xsysconf (_SC_PAGESIZE);
+  size_t stride_size = minimum_stride_size (page_size, element_size);
+  if (stride_size == 0)
+    {
+      errno = EOVERFLOW;
+      return (struct support_blob_repeat) { 0 };
+    }
+
+  /* Ensure that the stride size is at least maximum_small_size.  This
+     is necessary to reduce the number of distinct mappings.  */
+  if (stride_size < maximum_small_size)
+    stride_size
+      = ((maximum_small_size + stride_size - 1) / stride_size) * stride_size;
+
+  if (stride_size > total_size)
+    /* The mmap optimization would not save anything.  */
+    return allocate_malloc (total_size, element, element_size, count);
+
+  /* Reserve the memory region.  If we cannot create the mapping,
+     there is no reason to set up the backing file.  */
+  void *target = mmap (NULL, total_size, PROT_NONE,
+                       MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+  if (target == MAP_FAILED)
+    return (struct support_blob_repeat) { 0 };
+
+  /* Create the backing file for the repeated mapping.  */
+  int fd;
+  {
+    char *temppath;
+    fd = create_temp_file ("support_blob_repeat-", &temppath);
+    if (fd < 0)
+      FAIL_EXIT1 ("create_temp_file: %m");
+    xunlink (temppath);
+    free (temppath);
+  }
+
+  /* Make sure that there is backing storage, so that the fill
+     operation will not fault.  */
+  if (posix_fallocate (fd, 0, stride_size) != 0)
+    FAIL_EXIT1 ("posix_fallocate (%zu): %m", stride_size);
+
+  /* The stride size must still be a multiple of the page size and
+     element size.  */
+  TEST_VERIFY_EXIT ((stride_size % page_size) == 0);
+  TEST_VERIFY_EXIT ((stride_size % element_size) == 0);
+
+  /* Fill the backing store.  */
+  {
+    void *ptr = mmap (target, stride_size, PROT_READ | PROT_WRITE,
+                      MAP_FIXED | MAP_FILE | MAP_SHARED, fd, 0);
+    if (ptr == MAP_FAILED)
+      {
+        int saved_errno = errno;
+        xmunmap (target, total_size);
+        xclose (fd);
+        errno = saved_errno;
+        return (struct support_blob_repeat) { 0 };
+      }
+    if (ptr != target)
+      FAIL_EXIT1 ("mapping of %zu bytes moved from %p to %p",
+                  stride_size, target, ptr);
+
+    /* Write the repeating data.  */
+    fill (target, element, element_size, stride_size / element_size);
+
+    /* Return to a PROT_NONE mapping, just to be on the safe side.  */
+    ptr = mmap (target, stride_size, PROT_NONE,
+                MAP_FIXED | MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+    if (ptr == MAP_FAILED)
+      FAIL_EXIT1 ("Failed to reinstate PROT_NONE mapping: %m");
+    if (ptr != target)
+      FAIL_EXIT1 ("PROT_NONE mapping of %zu bytes moved from %p to %p",
+                  stride_size, target, ptr);
+  }
+
+  /* Create the alias mappings.  */
+  {
+    size_t remaining_size = total_size;
+    char *current = target;
+    int flags = MAP_FIXED | MAP_FILE | MAP_PRIVATE;
+#ifdef MAP_NORESERVE
+    flags |= MAP_NORESERVE;
+#endif
+    while (remaining_size > 0)
+      {
+        size_t to_map = stride_size;
+        if (to_map > remaining_size)
+          to_map = remaining_size;
+        void *ptr = mmap (current, to_map, PROT_READ | PROT_WRITE,
+                          flags, fd, 0);
+        if (ptr == MAP_FAILED)
+          {
+            int saved_errno = errno;
+            xmunmap (target, total_size);
+            xclose (fd);
+            errno = saved_errno;
+            return (struct support_blob_repeat) { 0 };
+          }
+        if (ptr != current)
+          FAIL_EXIT1 ("MAP_PRIVATE mapping of %zu bytes moved from %p to %p",
+                      to_map, target, ptr);
+        remaining_size -= to_map;
+        current += to_map;
+      }
+  }
+
+  xclose (fd);
+
+  return (struct support_blob_repeat)
+    {
+      .start = target,
+      .size = total_size,
+      .use_malloc = false
+    };
+}
+
+struct support_blob_repeat
+support_blob_repeat_allocate (const void *element, size_t element_size,
+                              size_t count)
+{
+  size_t total_size;
+  if (__builtin_mul_overflow (element_size, count, &total_size))
+    {
+      errno = EOVERFLOW;
+      return (struct support_blob_repeat) { 0 };
+    }
+  if (total_size <= maximum_small_size)
+    return allocate_malloc (total_size, element, element_size, count);
+  else
+    return allocate_big (total_size, element, element_size, count);
+}
+
+void
+support_blob_repeat_free (struct support_blob_repeat *blob)
+{
+  if (blob->size > 0)
+    {
+      int saved_errno = errno;
+      if (blob->use_malloc)
+        free (blob->start);
+      else
+        xmunmap (blob->start, blob->size);
+      errno = saved_errno;
+    }
+  *blob = (struct support_blob_repeat) { 0 };
+}

support/blob_repeat.h

@@ -0,0 +1,44 @@
+/* Repeating a memory blob, with alias mapping optimization.
+   Copyright (C) 2018 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
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef SUPPORT_BLOB_REPEAT_H
+#define SUPPORT_BLOB_REPEAT_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+struct support_blob_repeat
+{
+  void *start;
+  size_t size;
+  bool use_malloc;
+};
+
+/* Return an allocation of COUNT elements, each of ELEMENT_SIZE bytes,
+   initialized with the bytes starting at ELEMENT.  The memory is
+   writable (and thus counts towards the commit charge).  In case of
+   on error, all members of the return struct are zero-initialized,
+   and errno is set accordingly.  */
+struct support_blob_repeat support_blob_repeat_allocate (const void *element,
+                                                         size_t element_size,
+                                                         size_t count);
+
+/* Deallocate the blob created by support_blob_repeat_allocate.  */
+void support_blob_repeat_free (struct support_blob_repeat *);
+
+#endif /* SUPPORT_BLOB_REPEAT_H */

support/tst-support_blob_repeat.c

@@ -0,0 +1,85 @@
+/* Tests for <support/blob_repeat.h>
+   Copyright (C) 2018 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <support/blob_repeat.h>
+#include <support/check.h>
+
+static int
+do_test (void)
+{
+  struct support_blob_repeat repeat
+    = support_blob_repeat_allocate ("5", 1, 5);
+  TEST_COMPARE_BLOB (repeat.start, repeat.size, "55555", 5);
+  support_blob_repeat_free (&repeat);
+
+  repeat = support_blob_repeat_allocate ("ABC", 3, 3);
+  TEST_COMPARE_BLOB (repeat.start, repeat.size, "ABCABCABC", 9);
+  support_blob_repeat_free (&repeat);
+
+  repeat = support_blob_repeat_allocate ("abc", 4, 3);
+  TEST_COMPARE_BLOB (repeat.start, repeat.size, "abc\0abc\0abc", 12);
+  support_blob_repeat_free (&repeat);
+
+  size_t gigabyte = 1U << 30;
+  repeat = support_blob_repeat_allocate ("X", 1, gigabyte + 1);
+  if (repeat.start == NULL)
+    puts ("warning: not enough memory for 1 GiB mapping");
+  else
+    {
+      TEST_COMPARE (repeat.size, gigabyte + 1);
+      {
+        unsigned char *p = repeat.start;
+        for (size_t i = 0; i < gigabyte + 1; ++i)
+          if (p[i] != 'X')
+            FAIL_EXIT1 ("invalid byte 0x%02x at %zu", p[i], i);
+
+        /* Check that there is no sharing across the mapping.  */
+        p[0] = 'Y';
+        p[1U << 24] = 'Z';
+        for (size_t i = 0; i < gigabyte + 1; ++i)
+          if (i == 0)
+            TEST_COMPARE (p[i], 'Y');
+          else if (i == 1U << 24)
+            TEST_COMPARE (p[i], 'Z');
+          else if (p[i] != 'X')
+            FAIL_EXIT1 ("invalid byte 0x%02x at %zu", p[i], i);
+      }
+    }
+  support_blob_repeat_free (&repeat);
+
+  repeat = support_blob_repeat_allocate ("012345678", 9, 10 * 1000 * 1000);
+  if (repeat.start == NULL)
+    puts ("warning: not enough memory for large mapping");
+  else
+    {
+      unsigned char *p = repeat.start;
+      for (int i = 0; i < 10 * 1000 * 1000; ++i)
+        for (int j = 0; j <= 8; ++j)
+          if (p[i * 9 + j] != '0' + j)
+            {
+              printf ("error: element %d index %d\n", i, j);
+              TEST_COMPARE (p[i * 9 + j], '0' + j);
+            }
+    }
+  support_blob_repeat_free (&repeat);
+
+  return 0;
+}
+
+#include <support/test-driver.c>