[GCC-XML] Failure to handle __is_enum

Brad King brad.king at kitware.com
Mon Dec 22 14:22:01 EST 2008

Neal Becker wrote:
> On Monday 22 December 2008, Brad King wrote:
>> Neal Becker wrote:
>>> I have the current gcc_xml cvs.  It seems to choke on boost-1.37.0, where
>>> we use __is_enum if gcc is 4.3.
>>> Running on gccxml, it seems to identify itself as gcc4.3, but it doesn't
>>> seem to understand __is_enum builtin.
>>> What's the story here?  I think gccxml is really gcc4.2, and doesn't
>>> support this builtin?  In that case, how do I run gccxml and tell it to
>>> use the gcc4.2 config instead of gcc4.3?
>> gccxml uses a 4.2 parser internally.  It is non-trivial to update the
>> internal version so I do it only every few versions.
>> We simulate the preprocessing of the target compiler including its
>> system headers so that any code generation done based on the xml output
>> can compile with the target compiler.  In order to handle non-standard
>> code in native headers (including MSVC, Borland, and SGI) we copy them
>> into a gccxml support directory and patch them.  This approach has
>> worked well for years but gcc 4.3's headers use *alot* of
>> compiler-specific (4.3-only) extensions.
>> gccxml distinguishes itself from the preprocessor of the target compiler
>> by adding these definitions (documented in the man page):
>>   -D__GCCXML__=MMmmpp
>>          MM,  mm, and pp are the major, minor, and patch versions of GCC-
>>          XML.  This preprocessor symbol identifies GCC-XML to the  source
>>          code  as  it is preprocessed.  It can be used to enable GCC-XML-
>>          specific information.
>>   -D__GCCXML_GNUC__=M
>>          Defined to internal GCC parser major version.
>>          Defined to internal GCC parser minor version.
>>          Defined to internal GCC parser patchlevel.
>>  From boost's point of view gccxml is another compiler identified by the
>> above macros.  I know Boost.Config has some support for gccxml.  The
>> header in question needs to be updated to not use the builtin when the
>> compiler is identified as gccxml.  This is not the first time:
>>    https://svn.boost.org/trac/boost/ticket/907
>> For an immediate work-around you can install gcc 4.2 on your system and
>> tell gccxml to simulate it with the option "--gccxml-compiler g++4.2".
>> -Brad
> Wouldn't a simpler workaround be to patch the header, as you suggest above?

Yes.  That is actually a fix rather than a workaround :)

The reason I suggested the workaround is because you referred to a boost 
release version.  If you were working with others locked to that version 
then patching may not be an option.  Patch away, though.


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