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Postings from May 2008
On Tue, 27 May 2008, Dave Mitchell wrote: > On Fri, Feb 01, 2008 at 01:40:41PM -0800, Jan Dubois wrote: > > 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. > > > Jan, is this patch safe for 5.10.1 - specifically is it binary compatible? No, it is not. :( For 5.10 we'll have to live with the slightly bloated OP structures. Cheers, -JanThread Previous | Thread Next