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/**
* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
* SPDX-License-Identifier: Apache-2.0.
*/
/**
* FUNCTION: memcpy
*
* This function overrides the original implementation of the memcpy function
* from string.h. It copies the values of n bytes from the *src to the *dst.
* It also checks if the size of the arrays pointed to by both the *dst and
* *src parameters are at least n bytes and if they overlap.
*
* This takes advantage of the fact that 64bit operations require fewer array updates,
* which can make this version faster than the naive unrolling when used in CBMC.
* Benchmark your particular proof to know for sure.
*/
#include <stddef.h>
#include <stdint.h>
void *memcpy_using_uint64_impl(void *dst, const void *src, size_t n) {
__CPROVER_precondition(
__CPROVER_POINTER_OBJECT(dst) != __CPROVER_POINTER_OBJECT(src) ||
((const char *)src >= (const char *)dst + n) || ((const char *)dst >= (const char *)src + n),
"memcpy src/dst overlap");
__CPROVER_precondition(__CPROVER_r_ok(src, n), "memcpy source region readable");
__CPROVER_precondition(__CPROVER_w_ok(dst, n), "memcpy destination region writeable");
size_t num_uint64s = n >> 3;
size_t rem = n & 0x7;
uint8_t *d = (uint8_t *)dst;
const uint8_t *s = (const uint8_t *)src;
// Use fallthrough to unroll the remainder loop
switch (rem) {
case 7:
d[6] = s[6];
case 6:
d[5] = s[5];
case 5:
d[4] = s[4];
case 4:
d[3] = s[3];
case 3:
d[2] = s[2];
case 2:
d[1] = s[1];
case 1:
d[0] = s[0];
}
d += rem;
s += rem;
for (size_t i = 0; i < num_uint64s; ++i) {
((uint64_t *)d)[i] = ((const uint64_t *)s)[i];
}
return dst;
}
void *memcpy(void *dst, const void *src, size_t n) {
return memcpy_using_uint64_impl(dst, src, n);
}
void *__builtin___memcpy_chk(void *dst, const void *src, __CPROVER_size_t n, __CPROVER_size_t size) {
(void)size;
return memcpy_using_uint64_impl(dst, src, n);
}
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