302 lines
9.4 KiB
C
302 lines
9.4 KiB
C
/* Repeating a memory blob, with alias mapping optimization.
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Copyright (C) 2018-2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <errno.h>
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#include <fcntl.h>
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#include <stdbool.h>
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#include <stdlib.h>
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#include <string.h>
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#include <support/blob_repeat.h>
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#include <support/check.h>
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#include <support/test-driver.h>
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#include <support/support.h>
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#include <support/xunistd.h>
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#include <sys/mman.h>
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#include <unistd.h>
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#include <wchar.h>
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/* Small allocations should use malloc directly instead of the mmap
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optimization because mappings carry a lot of overhead. */
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static const size_t maximum_small_size = 4 * 1024 * 1024;
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/* Internal helper for fill. */
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static void
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fill0 (char *target, const char *element, size_t element_size,
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size_t count)
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{
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while (count > 0)
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{
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memcpy (target, element, element_size);
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target += element_size;
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--count;
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}
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}
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/* Fill the buffer at TARGET with COUNT copies of the ELEMENT_SIZE
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bytes starting at ELEMENT. */
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static void
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fill (char *target, const char *element, size_t element_size,
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size_t count)
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{
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if (element_size == 0 || count == 0)
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return;
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else if (element_size == 1)
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memset (target, element[0], count);
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else if (element_size == sizeof (wchar_t))
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{
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wchar_t wc;
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memcpy (&wc, element, sizeof (wc));
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wmemset ((wchar_t *) target, wc, count);
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}
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else if (element_size < 1024 && count > 4096)
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{
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/* Use larger copies for really small element sizes. */
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char buffer[8192];
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size_t buffer_count = sizeof (buffer) / element_size;
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fill0 (buffer, element, element_size, buffer_count);
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while (count > 0)
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{
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size_t copy_count = buffer_count;
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if (copy_count > count)
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copy_count = count;
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size_t copy_bytes = copy_count * element_size;
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memcpy (target, buffer, copy_bytes);
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target += copy_bytes;
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count -= copy_count;
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}
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}
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else
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fill0 (target, element, element_size, count);
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}
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/* Use malloc instead of mmap for small allocations and unusual size
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combinations. */
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static struct support_blob_repeat
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allocate_malloc (size_t total_size, const void *element, size_t element_size,
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size_t count)
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{
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void *buffer = malloc (total_size);
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if (buffer == NULL)
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return (struct support_blob_repeat) { 0 };
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fill (buffer, element, element_size, count);
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return (struct support_blob_repeat)
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{
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.start = buffer,
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.size = total_size,
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.use_malloc = true
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};
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}
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/* Return the least common multiple of PAGE_SIZE and ELEMENT_SIZE,
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avoiding overflow. This assumes that PAGE_SIZE is a power of
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two. */
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static size_t
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minimum_stride_size (size_t page_size, size_t element_size)
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{
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TEST_VERIFY_EXIT (page_size > 0);
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TEST_VERIFY_EXIT (element_size > 0);
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/* Compute the number of trailing zeros common to both sizes. */
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unsigned int common_zeros = __builtin_ctzll (page_size | element_size);
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/* In the product, this power of two appears twice, but in the least
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common multiple, it appears only once. Therefore, shift one
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factor. */
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size_t multiple;
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if (__builtin_mul_overflow (page_size >> common_zeros, element_size,
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&multiple))
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return 0;
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return multiple;
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}
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/* Allocations larger than maximum_small_size potentially use mmap
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with alias mappings. If SHARED, the alias mappings are created
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using MAP_SHARED instead of MAP_PRIVATE. */
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static struct support_blob_repeat
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allocate_big (size_t total_size, const void *element, size_t element_size,
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size_t count, bool shared)
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{
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unsigned long page_size = xsysconf (_SC_PAGESIZE);
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size_t stride_size = minimum_stride_size (page_size, element_size);
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if (stride_size == 0)
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{
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errno = EOVERFLOW;
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return (struct support_blob_repeat) { 0 };
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}
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/* Ensure that the stride size is at least maximum_small_size. This
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is necessary to reduce the number of distinct mappings. */
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if (stride_size < maximum_small_size)
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stride_size
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= ((maximum_small_size + stride_size - 1) / stride_size) * stride_size;
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if (stride_size > total_size)
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/* The mmap optimization would not save anything. */
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return allocate_malloc (total_size, element, element_size, count);
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/* Reserve the memory region. If we cannot create the mapping,
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there is no reason to set up the backing file. */
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void *target = mmap (NULL, total_size, PROT_NONE,
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MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
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if (target == MAP_FAILED)
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return (struct support_blob_repeat) { 0 };
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/* Create the backing file for the repeated mapping. Call mkstemp
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directly to remove the resources backing the temporary file
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immediately, once support_blob_repeat_free is called. Using
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create_temp_file would result in a warning during post-test
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cleanup. */
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int fd;
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{
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char *temppath = xasprintf ("%s/support_blob_repeat-XXXXXX", test_dir);
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fd = mkstemp (temppath);
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if (fd < 0)
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FAIL_EXIT1 ("mkstemp (\"%s\"): %m", temppath);
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xunlink (temppath);
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free (temppath);
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}
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/* Make sure that there is backing storage, so that the fill
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operation will not fault. */
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if (posix_fallocate (fd, 0, stride_size) != 0)
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FAIL_EXIT1 ("posix_fallocate (%zu): %m", stride_size);
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/* The stride size must still be a multiple of the page size and
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element size. */
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TEST_VERIFY_EXIT ((stride_size % page_size) == 0);
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TEST_VERIFY_EXIT ((stride_size % element_size) == 0);
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/* Fill the backing store. */
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{
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void *ptr = mmap (target, stride_size, PROT_READ | PROT_WRITE,
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MAP_FIXED | MAP_FILE | MAP_SHARED, fd, 0);
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if (ptr == MAP_FAILED)
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{
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int saved_errno = errno;
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xmunmap (target, total_size);
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xclose (fd);
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errno = saved_errno;
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return (struct support_blob_repeat) { 0 };
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}
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if (ptr != target)
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FAIL_EXIT1 ("mapping of %zu bytes moved from %p to %p",
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stride_size, target, ptr);
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/* Write the repeating data. */
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fill (target, element, element_size, stride_size / element_size);
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/* Return to a PROT_NONE mapping, just to be on the safe side. */
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ptr = mmap (target, stride_size, PROT_NONE,
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MAP_FIXED | MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
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if (ptr == MAP_FAILED)
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FAIL_EXIT1 ("Failed to reinstate PROT_NONE mapping: %m");
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if (ptr != target)
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FAIL_EXIT1 ("PROT_NONE mapping of %zu bytes moved from %p to %p",
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stride_size, target, ptr);
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}
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/* Create the alias mappings. */
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{
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size_t remaining_size = total_size;
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char *current = target;
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int flags = MAP_FIXED | MAP_FILE;
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if (shared)
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flags |= MAP_SHARED;
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else
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flags |= MAP_PRIVATE;
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#ifdef MAP_NORESERVE
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flags |= MAP_NORESERVE;
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#endif
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while (remaining_size > 0)
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{
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size_t to_map = stride_size;
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if (to_map > remaining_size)
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to_map = remaining_size;
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void *ptr = mmap (current, to_map, PROT_READ | PROT_WRITE,
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flags, fd, 0);
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if (ptr == MAP_FAILED)
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{
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int saved_errno = errno;
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xmunmap (target, total_size);
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xclose (fd);
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errno = saved_errno;
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return (struct support_blob_repeat) { 0 };
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}
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if (ptr != current)
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FAIL_EXIT1 ("MAP_PRIVATE mapping of %zu bytes moved from %p to %p",
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to_map, target, ptr);
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remaining_size -= to_map;
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current += to_map;
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}
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}
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xclose (fd);
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return (struct support_blob_repeat)
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{
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.start = target,
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.size = total_size,
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.use_malloc = false
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};
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}
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struct support_blob_repeat
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repeat_allocate (const void *element, size_t element_size,
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size_t count, bool shared)
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{
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size_t total_size;
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if (__builtin_mul_overflow (element_size, count, &total_size))
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{
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errno = EOVERFLOW;
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return (struct support_blob_repeat) { 0 };
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}
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if (total_size <= maximum_small_size)
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return allocate_malloc (total_size, element, element_size, count);
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else
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return allocate_big (total_size, element, element_size, count, shared);
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}
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struct support_blob_repeat
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support_blob_repeat_allocate (const void *element, size_t element_size,
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size_t count)
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{
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return repeat_allocate (element, element_size, count, false);
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}
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struct support_blob_repeat
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support_blob_repeat_allocate_shared (const void *element, size_t element_size,
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size_t count)
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{
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return repeat_allocate (element, element_size, count, true);
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}
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void
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support_blob_repeat_free (struct support_blob_repeat *blob)
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{
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if (blob->size > 0)
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{
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int saved_errno = errno;
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if (blob->use_malloc)
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free (blob->start);
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else
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xmunmap (blob->start, blob->size);
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errno = saved_errno;
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}
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*blob = (struct support_blob_repeat) { 0 };
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}
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