Date: Wed, 1 Jun 2011 11:44:12 -0400 From: Alexander Kabaev <kabaev@gmail.com> To: Marcel Moolenaar <marcel@xcllnt.net> Cc: mdf@freebsd.org, Evans <brde@optusnet.com.au>, Bruce@freebsd.org, freebsd-hackers <freebsd-hackers@freebsd.org> Subject: Re: sizeof(function pointer) Message-ID: <20110601114412.7de0b349@kan.dnsalias.net> In-Reply-To: <CC5909A8-5A5D-4859-9769-132BF88B559E@xcllnt.net> References: <BANLkTimctcBWRrYVLyc-WLgePyCXqaPTGA@mail.gmail.com> <D541877D-0EE5-4EC3-9197-E9F2A7A10AC1@bsdimp.com> <20110531200652.3fd6fcbe@kan.dnsalias.net> <CC5909A8-5A5D-4859-9769-132BF88B559E@xcllnt.net>
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[-- Attachment #1 --] On Tue, 31 May 2011 21:09:10 -0700 Marcel Moolenaar <marcel@xcllnt.net> wrote: > > On May 31, 2011, at 5:06 PM, Alexander Kabaev wrote: > >> Usually it is different only on segmented architectures like 16-bit > >> x86. > >> > > > > Not so on ia64, where they have special function descriptor type. > > Actually, no. On ia64 a function pointer has the same size as a > data pointer. It's just that a function pointer does not point > to the actual function (i.e. the first instruction of a function), > but to a function descriptor. The function descriptor contains the > address of the actual function and the value of the GP register > that needs to be set before entering the function. > > As such, only virtual functions in C++ are impacted by this. The > function descriptor needs to be stored in the object instead of > the function pointer in that case. > > FYI, > > -- Oh, you are correct. I forgot the double indirection we do to support that in dlsym, where we are maintain our own 'virtual table' of function descriptors within rtld itself. -- Alexander Kabaev [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.17 (FreeBSD) iD8DBQFN5l5QQ6z1jMm+XZYRAjgVAJ9KOZOAbApte9l7IAQS4DzNqVVsHACfXNfw mhWAgk2PlN+4EAtGt9wIf0U= =P2pN -----END PGP SIGNATURE-----
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