fix memmove large-length backward copy

F/1897

Author: danielinux

src/string.c

@@ -288,14 +288,14 @@ void RAMFUNCTION *memcpy(void *dst, const void *src, size_t n)
     !defined(__CCRX__)
 void *memmove(void *dst, const void *src, size_t n)
 {
-    int i;
+    size_t i;
     if (dst == src)
         return dst;
     if (src < dst)  {
         const char *s = (const char *)src;
         char *d = (char *)dst;
-        for (i = n - 1; i >= 0; i--) {
-            d[i] = s[i];
+        for (i = n; i > 0; i--) {
+            d[i - 1] = s[i - 1];
         }
         return dst;
     } else {

tools/unit-tests/unit-string.c

@@ -25,8 +25,12 @@
 #define FAST_MEMCPY
 
 #include <check.h>
+#include <limits.h>
 #include <stdint.h>
 #include <string.h>
+#ifdef __linux__
+#include <sys/mman.h>
+#endif
 
 #include "string.c"
 
@@ -325,6 +329,31 @@ START_TEST(test_memcpy_memmove)
 }
 END_TEST
 
+#if defined(__linux__) && (SIZE_MAX > INT_MAX)
+START_TEST(test_memmove_large_overlap_length)
+{
+    size_t n = (size_t)INT_MAX + 2U;
+    size_t len = n + 1U;
+    unsigned char *region = mmap(NULL, len, PROT_READ | PROT_WRITE,
+        MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+
+    ck_assert_ptr_ne(region, MAP_FAILED);
+
+    region[0] = 0x11;
+    region[1] = 0x22;
+    region[n - 1] = 0x33;
+    region[n] = 0x44;
+
+    memmove(region + 1, region, n);
+
+    ck_assert_uint_eq(region[1], 0x11);
+    ck_assert_uint_eq(region[n], 0x33);
+
+    ck_assert_int_eq(munmap(region, len), 0);
+}
+END_TEST
+#endif
+
 START_TEST(test_memcpy_aligned_buffers)
 {
     union {
@@ -443,6 +472,9 @@ Suite *string_suite(void)
     tcase_add_test(tcase_misc, test_strcpy_strncpy_strcat_strncat);
     tcase_add_test(tcase_misc, test_strncmp);
     tcase_add_test(tcase_misc, test_memcpy_memmove);
+#if defined(__linux__) && (SIZE_MAX > INT_MAX)
+    tcase_add_test(tcase_misc, test_memmove_large_overlap_length);
+#endif
     tcase_add_test(tcase_misc, test_memcpy_aligned_buffers);
     tcase_add_test(tcase_misc, test_uart_writenum_basic);
     tcase_add_test(tcase_misc, test_uart_printf_formats);