string_override.c

// SPDX-License-Identifier: GPL-2.0-only
#include <stddef.h>

/*
 * Override the "basic" built-in string helpers so that they can be used in
 * guest code.  KVM selftests don't support dynamic loading in guest code and
 * will jump into the weeds if the compiler decides to insert an out-of-line
 * call via the PLT.
 */
int memcmp(const void *cs, const void *ct, size_t count)
{
	const unsigned char *su1, *su2;
	int res = 0;

	for (su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--) {
		if ((res = *su1 - *su2) != 0)
			break;
	}
	return res;
}

void *memcpy(void *dest, const void *src, size_t count)
{
	char *tmp = dest;
	const char *s = src;

	while (count--)
		*tmp++ = *s++;
	return dest;
}

void *memset(void *s, int c, size_t count)
{
	char *xs = s;

	while (count--)
		*xs++ = c;
	return s;
}

size_t strnlen(const char *s, size_t count)
{
	const char *sc;

	for (sc = s; count-- && *sc != '\0'; ++sc)
		/* nothing */;
	return sc - s;
}