GCC process not working as expected when called in Python (3.1.2) subprocess-shell, but OK otherwise

[Kingsley Turner]

  Hi,

I'm using GCC as a pre-processor for a C-like language (EDDL) to handle all 
the includes, macros, etc. producing a single source file for another 
compiler.  My python code massages the inputs (which arrive in a .zip file), 
then calls GCC.

I have a problem where if I call GCC from my python script some of the 
#defines are not processed in the output.  However if I paste the exact same 
GCC command-line into a shell, I get a correct output.

I'm calling GCC in this manner:

     ### Execute GCC, keep stdout & stderr
     err_out = open(error_filename,"wb")
     process = subprocess.Popen(gcc_command, stderr=err_out, bufsize=81920, 
cwd=global_options['tmp'])
     gcc_exit_code = process.wait()
     log("GCC Exit Code %u" % (gcc_exit_code))
     err_out.close()

where gcc_command is:

     "/usr/bin/gcc -I /tmp/dd-compile_1286930109.99 -I 
/home/foo/eddl-includes -D__TOKVER__=600 -ansi -nostdinc -v -x c -E -o 
/tmp/dd-compile_1286930109.99/11130201.ddl.OUT 
/tmp/dd-compile_1286930109.99/11130201.ddl"

So when this code spawns GCC, the compiler does not really work 100%, but if 
I paste this exact command line, the output is perfect.

I'm not really sure how to debug this.  I already checked the ulimits, and 
permissions shouldn't be a problem since it's all run by the same user, I 
also checked the environment - these were copied into the subshell.

GCC produces no warnings, or errors.  The output is mostly OK, some other 
macros have been processed.
If I diff the working output with the non-working one, the differences are 
only a bunch of skipped #defines.

gcc version 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu5)
Python 3.1.2 (release31-maint, Sep 17 2010, 20:27:33)
Linux 2.6.35-22-generic #34-Ubuntu SMP Sun Oct 10 09:26:05 UTC 2010 x86_64 
GNU/Linux

Any suggestions for helping me debug this would be much appreciated.

thanks,
-kt

PS> this query has also been posted to the GCC-help list