6 files changed, 33 insertions, 31 deletions

diff --git a/include/string.h b/include/string.h
index 9cb0598..75dadab 100644
--- a/include/string.h
+++ b/include/string.h
@@ -189,19 +189,17 @@ _FORTIFY_FN(stpncpy) char *stpncpy(char * _FORTIFY_POS0 __d, const char *__s,
 #if __has_builtin(__builtin___stpncpy_chk) && USE_NATIVE_CHK
         return __builtin___stpncpy_chk(__d, __s, __n, __fh_bos(__d, 0));
 #else
-#if 0
-        // They check overlap across the whole range of the given length, but
-        // the given length is not what will actually be copied, rather it's
-        // the maximum length (if src is shorter, only length of src will be
-        // copied). This triggers false positives and traps where it shouldn't
-        // (e.g. in ICU tests).
-        if (__fh_overlap(__d, __s, __n))
+        __fh_size_t max_len_s = strnlen(__s, __n);
+        if (__fh_overlap(__d, max_len_s, __s, max_len_s))
                 __builtin_trap();
-#endif
 
+        // If the length strlen(src) is smaller than n, the remaining
+        // characters in the array pointed to by dest are filled with null
+        // bytes ('\0')
         __fh_size_t __b = __fh_bos(__d, 0);
-        if (__n > __b && strlen(__s) + 1 > __b)
+        if (__n > __b)
                 __builtin_trap();
+
         return __orig_stpncpy(__d, __s, __n);
 #endif
 }
@@ -297,19 +295,16 @@ _FORTIFY_FN(strncpy) char *strncpy(char * _FORTIFY_POS0 __d,
 #if __has_builtin(__builtin___strncpy_chk) && USE_NATIVE_CHK
         return __builtin___strncpy_chk(__d, __s, __n, __fh_bos(__d, 0));
 #else
-#if 0
-        // They check overlap across the whole range of the given length, but
-        // the given length is not what will actually be copied, rather it's
-        // the maximum length (if src is shorter, only length of src will be
-        // copied). This triggers false positives and traps where it shouldn't
-        // (e.g. in ICU tests).
-        if (__fh_overlap(__d, __s, __n))
+        __fh_size_t max_len_s = strnlen(__s, __n);
+        if (__fh_overlap(__d, max_len_s, __s, max_len_s))
                 __builtin_trap();
-#endif
 
+        // If the length of src is less than n, strncpy() writes additional
+        // null bytes to dest to ensure that a total of n bytes are written.
         __fh_size_t __b = __fh_bos(__d, 0);
         if (__n > __b)
                 __builtin_trap();
+
         return __orig_strncpy(__d, __s, __n);
 #endif
 }
diff --git a/tests/test_stpncpy_dynamic_write.c b/tests/test_stpncpy_dynamic_write.c
index 8fbfe7e..14f6fd9 100644
--- a/tests/test_stpncpy_dynamic_write.c
+++ b/tests/test_stpncpy_dynamic_write.c
@@ -3,8 +3,9 @@
 #include <string.h>
 
 int main(int argc, char** argv) {
-  char buffer[8] = {0};
-  stpncpy(buffer, "1234567", 5);
+  char buffer[] = {'A', 'B', 'C', 'D', 'E', 'F', '\0'};
+
+  stpncpy(buffer, "1234567", 3);
   puts(buffer);
 
   CHK_FAIL_START
diff --git a/tests/test_stpncpy_overwrite_over.c b/tests/test_stpncpy_overwrite_over.c
index 004e2b8..21c88ce 100644
--- a/tests/test_stpncpy_overwrite_over.c
+++ b/tests/test_stpncpy_overwrite_over.c
@@ -3,15 +3,16 @@
 #include <string.h>
 
 int main(int argc, char** argv) {
-#if 0
   char buffer[9] = {'A', 'A', 'A', 'A', 'B', 'B', 'B', 'B', '\0'};
   puts(buffer);
 
+  stpncpy(buffer, buffer+5, 2);
+  puts(buffer);
+
   CHK_FAIL_START
   stpncpy(buffer+1, buffer, 5);
   CHK_FAIL_END
 
   puts(buffer);
-#endif
   return ret;
 }
diff --git a/tests/test_stpncpy_overwrite_under.c b/tests/test_stpncpy_overwrite_under.c
index 845ae29..3b435de 100644
--- a/tests/test_stpncpy_overwrite_under.c
+++ b/tests/test_stpncpy_overwrite_under.c
@@ -3,15 +3,17 @@
 #include <string.h>
 
 int main(int argc, char** argv) {
-#if 0
   char buffer[9] = {'A', 'A', 'A', 'A', 'B', 'B', 'B', 'B', '\0'};
   puts(buffer);
 
+  stpncpy(buffer+5, buffer, 2);
+  puts(buffer);
+
+  char buffer2[] = {'A', 'A', 'A', 'A', 'B', 'B', 'B', 'B', '\0'};
   CHK_FAIL_START
-  stpncpy(buffer-1, buffer, 5);
+  stpncpy(buffer2-1, buffer2, 5);
   CHK_FAIL_END
 
-  puts(buffer);
-#endif
+  puts(buffer2);
   return ret;
 }
diff --git a/tests/test_strncpy_overwrite_over.c b/tests/test_strncpy_overwrite_over.c
index 94b6d2b..d99d270 100644
--- a/tests/test_strncpy_overwrite_over.c
+++ b/tests/test_strncpy_overwrite_over.c
@@ -3,15 +3,20 @@
 #include <string.h>
 
 int main(int argc, char** argv) {
-#if 0
   char buffer[9] = {'A', 'A', 'A', 'A', 'B', 'B', 'B', 'B', '\0'};
   puts(buffer);
 
+  strncpy(buffer, buffer+4, 1);
+  puts(buffer);
+
+  strncpy(buffer+6, buffer, 1);
+  puts(buffer);
+
+  char buffer2[9] = {'A', 'A', 'A', 'A', 'B', 'B', 'B', 'B', '\0'};
   CHK_FAIL_START
-  strncpy(buffer+1, buffer, 5);
+  strncpy(buffer2+1, buffer2, 5);
   CHK_FAIL_END
 
-  puts(buffer);
-#endif
+  puts(buffer2);
   return ret;
 }
diff --git a/tests/test_strncpy_overwrite_under.c b/tests/test_strncpy_overwrite_under.c
index 8a0a4af..f554b28 100644
--- a/tests/test_strncpy_overwrite_under.c
+++ b/tests/test_strncpy_overwrite_under.c
@@ -3,7 +3,6 @@
 #include <string.h>
 
 int main(int argc, char** argv) {
-#if 0
   char buffer[9] = {'A', 'A', 'A', 'A', 'B', 'B', 'B', 'B', '\0'};
   puts(buffer);
 
@@ -12,6 +11,5 @@ int main(int argc, char** argv) {
   CHK_FAIL_END
 
   puts(buffer);
-#endif
   return ret;
 }