/* 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/test-driver.h>

#include <support/support.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.  Call mkstemp

     directly to remove the resources backing the temporary file

     immediately, once support_blob_repeat_free is called.  Using

     create_temp_file would result in a warning during post-test

     cleanup.  */

  int fd;

  {

    char *temppath = xasprintf ("%s/support_blob_repeat-XXXXXX", test_dir);

    fd = mkstemp (temppath);

    if (fd < 0)

      FAIL_EXIT1 ("mkstemp (\"%s\"): %m", temppath);

    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 };

}