stray warning from gcc's cpp

[Andriy Gapon <avg at FreeBSD dot org>]

I observe the following minor annoyance on FreeBSD systems where cpp is GCC's
cpp.  If a DTrace script has the following shebang line:
#!/usr/sbin/dtrace -Cs
then the following warning is produced when the script is run:
cc1: warning:  is shorter than expected

Some details.  dtrace(1) first forks. Then a child seeks on a file descriptor
associated with the script file, so that the shebang line is skipped (because
otherwise it would confuse cpp).  Then the child makes the file descriptor its
standard input and then it execs cpp.  cpp performs fstat(2) on its standard
input descriptor and determines that it points to a regular file.  Then it
verifies that a number of bytes it reads from the file is the same as a size of
the file.  The check makes sense if the file is opened by cpp itself, but it
does not always make sense for the stdin as described above.

The following patch seems to fix the issue, but perhaps there is a better /
smarter alternative.

--- a/libcpp/files.c
+++ b/libcpp/files.c
@@ -601,7 +601,8 @@ read_file_guts (cpp_reader *pfile, _cpp_file *file)
       return false;
     }

-  if (regular && total != size && STAT_SIZE_RELIABLE (file->st))
+  if (regular && total != size && file->fd != 0
+      && STAT_SIZE_RELIABLE (file->st))
     cpp_error (pfile, CPP_DL_WARNING,
 	       "%s is shorter than expected", file->path);


-- 
Andriy Gapon