On Tue, 31 May 2011 17:18:16 -0600 Warner Losh <i...@bsdimp.com> wrote:
> > On May 31, 2011, at 5:07 PM, 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. > > 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. > Not so on ia64, where they have special function descriptor type. -- Alexander Kabaev
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