On 01/06/2011 00:07, m...@freebsd.org 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.
You could add a static-assert to check for this at compile-time: http://stackoverflow.com/questions/3385515/static-assert-in-c e.g. something like: STATIC_ASSERT(sizeof(void *) == sizeof(int(*)(void)),ptr_to_func_expected_to_be_same_size_as_data_ptr); I've only used static-assert-like constructs in C++, so don't know how well they behave in C... -- Sent from my <insert random gadget here> _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"
