Re: stray warning from gcc's cpp

[Gerald Pfeifer <gerald at pfeifer dot com>]

Hi David,

I found this older report (including patches for two approaches
even!) that it seems did not see any response despite the nice
analysis (and the patch).

Mind having a look?

Gerald

PS: If you prefer, I can put this into Bugzilla, too.

On Fri, 28 Mar 2014, Andriy Gapon wrote:
> on 19/03/2014 12:03 Andriy Gapon said the following:
>> 
>> 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 patch that implements a different approach has been committed in FreeBSD:
> https://github.com/freebsd/freebsd/commit/6ceec4444ddbc
> Please consider.  Thanks!
> 
>> --- 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);