diff --git a/userspace/libc.h b/userspace/libc.h
index 411ac0e..2b431c0 100644
--- a/userspace/libc.h
+++ b/userspace/libc.h
@@ -13,15 +13,15 @@
 #define EOF (-1)
 
 
-int memcmp(const void *s1, const void *s2, size_t n);
-void *memcpy(void *dest, const void *src, size_t n);
-void *memset(void *s, int c, size_t n);
+__attribute__ ((access (read_only, 1, 3), access (read_only, 2, 3))) int memcmp(const void *s1, const void *s2, size_t n);
+__attribute__ ((access (write_only, 1, 3), access (read_only, 2, 3))) void *memcpy(void *dest, const void *src, size_t n);
+__attribute__ ((access (write_only, 1, 3))) void *memset(void *s, int c, size_t n);
 char *itoa(long long int value, char *str, int base);
 void reverse(char s[]);
 int strlen(const char s[]);
-unsigned int strnlen(const char *s, size_t count);
+__attribute__ ((access (read_only, 1, 2))) unsigned int strnlen(const char *s, size_t count);
 int strcmp(const char s1[], const char s2[]);
-char *strzcpy(char *dst, const char *src, int len);
+__attribute__ ((access (read_only, 2), access (write_only, 1, 3))) char *strzcpy(char *dst, const char *src, int len);
 int puts(const char *str);
 int putc(const int c);
 int vsnprintf(char *str, size_t size, const char *format, va_list ap);