On May 31, 2011, at 5:07 PM, [email protected] wrote: > I am looking into potentially MFC'ing r212367 and related, that adds > drains to sbufs. The reason for MFC is that several pieces of new > code in CURRENT are using the drain functionality and it would make > MFCing those changes much easier. > > The problem is that r212367 added a pointer to a drain function in the > sbuf (it replaced a pointer to void). The C standard doesn't > guarantee that a void * and a function pointer have the same size, > though its true on amd64, i386 and I believe PPC. What I'm wondering > is, though not guaranteed by the standard, is it *practically* true > that sizeof(void *) == sizeof(int(*)(void)), such that an MFC won't > break binary compatibility for any supported architecture? (The > standard does guarantee, though not in words, that all function > pointers have the same size, since it guarantees that pointers to > functions can be cast to other pointers to functions and back without > changing the value). > > Another possibility is to malloc a blob that is sizeof(int(*)(void)) > and store that in a renamed s_unused; this is a bit messier but > guaranteed to work. I'd just rather the code be an MCF instead of a > partial re-write.
It is the same on MIPS too for all three ABIs that we support (and all ABIs that I know about). It is true on ARM as well. Usually it is different only on segmented architectures like 16-bit x86. Warner_______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[email protected]"
