OpenE2K
/
glibc
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity
glibc/support/blob_repeat.c

283 lines
8.9 KiB
C
Raw Permalink Blame History

/* Repeating a memory blob, with alias mapping optimization.
Copyright (C) 2018-2019 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 };
}
Reference in New Issue View Git Blame Copy Permalink