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From: Tijl Coosemans <tijl@coosemans.org>
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Cc: mdf@freebsd.org, Bruce Evans <brde@optusnet.com.au>
Subject: Re: sizeof(function pointer)
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On Wednesday 01 June 2011 01:07:29 mdf@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.
>=20
> 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 *) =3D=3D sizeof(int(*)(void)), such that an MFC won't
> break binary compatibility for any supported architecture?

It's guaranteed by POSIX.

http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html
Section 2.12.3

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