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Postings from February 2008
On Wed, 30 Jan 2008, Jan Dubois wrote: > This is not really a core Perl bug; the problem is that VC++ and GCC > are incompatible as far as bit-fields are concerned. In Perl 5.10 > the BASEOP structure contains bitfields: > > unsigned op_type:9; \ > unsigned op_opt:1; \ > unsigned op_latefree:1; \ > unsigned op_latefreed:1; \ > unsigned op_attached:1; \ > unsigned op_spare:3; \ > > In VC++ the combined size of the fields above is 4 bytes, whereas > in GCC it is only 2. This also pushes the size of the complete > structure from 20 to 24 bytes for VC++. [...] > VC++ uses the base type (unsigned int, in this case) to determine > the alignment requirements and total size of the combined bit-field. > You can use the non-standard extension of using smaller integer sizes > to force the fields into a smaller size and different alignment. > In this case using "unsigned short" for the type of the bit-fields > should work. > > I guess for Perl 5.12 we need a way to let us use the smaller base > size for VC++ to keep the size of the OP structure down. I'll create > a patch for it eventually, when I get a bit more time. I also need > to check if there are other places where Perl is now using bit fields > in its structure definitions. I've attached a patch that defined PERL_BITFIELD8, PERL_BITFIELD16 and PERL_BITFIELD32 symbols to be used to specify bitfields whose base size and alignment requirements are 1, 2 or 4 bytes respectively. The "PERL_" prefix is a bit awkward, but these are names that must be defined even when PERL_CORE is not. These symbols are then being redefined for VC (and MinGW GCC) to use the corresponding smaller sizes as the base types. I've also added -mms-bitfields to the default options for MinGW in makefile.mk. That way building additional XS modules that interface to VC compatible libraries using bit-fields in their external APIs should be easier. Cheers, -JanThread Previous | Thread Next