Index: gcc/gcov.c
===================================================================
--- gcc/gcov.c	(revision 206281)
+++ gcc/gcov.c	(working copy)
@@ -2382,12 +2382,25 @@ read_line (FILE *file)
     {
       size_t len = strlen (string + pos);
 
+      /* If fgets returns non-zero but the string has zero length,
+	 we have a line that starts with a NUL character.
+	 Return NULL in this case.  */
+      if (len == 0)
+	return NULL;
       if (string[pos + len - 1] == '\n')
 	{
 	  string[pos + len - 1] = 0;
 	  return string;
 	}
       pos += len;
+      /* If fgets returns a short line without NL at the end, and the
+	 file pointer is at EOF, we might have an incomplete last line,
+	 or we have a NUL character on the last line.
+	 Return the string as usual in this case.
+	 However if the file is not at EOF we have a line with an
+	 embedded NUL character.  Return NULL in this case.  */
+      if (pos < string_len - 1)
+	return feof (file) ? string : NULL;
       string = XRESIZEVEC (char, string, string_len * 2);
       string_len *= 2;
     }
Index: gcc/input.c
===================================================================
--- gcc/input.c	(revision 206281)
+++ gcc/input.c	(working copy)
@@ -106,12 +106,25 @@ read_line (FILE *file)
     {
       size_t len = strlen (string + pos);
 
+      /* If fgets returns non-zero but the string has zero length,
+	 we have a line that starts with a NUL character.
+	 Return NULL in this case.  */
+      if (len == 0)
+	return NULL;
       if (string[pos + len - 1] == '\n')
 	{
 	  string[pos + len - 1] = 0;
 	  return string;
 	}
       pos += len;
+      /* If fgets returns a short line without NL at the end, and the
+	 file pointer is at EOF, we might have an incomplete last line,
+	 or we have a NUL character on the last line.
+	 Return the string as usual in this case.
+	 However if the file is not at EOF we have a line with an
+	 embedded NUL character.  Return NULL in this case.  */
+      if (pos < string_len - 1)
+	return feof (file) ? string : NULL;
       string = XRESIZEVEC (char, string, string_len * 2);
       string_len *= 2;
     }