Date: Tue, 31 May 2011 21:09:10 -0700 From: Marcel Moolenaar <marcel@xcllnt.net> To: Alexander Kabaev <kabaev@gmail.com> 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: <CC5909A8-5A5D-4859-9769-132BF88B559E@xcllnt.net> In-Reply-To: <20110531200652.3fd6fcbe@kan.dnsalias.net> References: <BANLkTimctcBWRrYVLyc-WLgePyCXqaPTGA@mail.gmail.com> <D541877D-0EE5-4EC3-9197-E9F2A7A10AC1@bsdimp.com> <20110531200652.3fd6fcbe@kan.dnsalias.net>
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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, -- Marcel Moolenaar marcel@xcllnt.net
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