Re: Returning values from objc_msgSend etc
Re: Returning values from objc_msgSend etc
- Subject: Re: Returning values from objc_msgSend etc
- From: "Sherm Pendley" <email@hidden>
- Date: Mon, 3 Mar 2008 06:54:22 -0500
On Mon, Mar 3, 2008 at 6:10 AM, Ronald Oussoren <email@hidden>
wrote:
>
> On Monday, March 03, 2008, at 11:53AM, "Duncan McGregor" <
> email@hidden> wrote:
>
> >> I can simply check the calculated size after calling ffi_prep_cif(),
> and compare that to sizeof(void*) to see if the return value will fit in a
> register.
> >
> >Is that right? 8 byte structs are returned in EAX and EDX on IA-32, so
> >I'd expect to call objc_msgSend.
>
> The rules are a bit more complex than this (at least on x86). Small
> structs are returned in registers (upto 8 bytes), but only if the size of
> the struct is a power of 2. That is, a 6-byte struct will not be returned in
> registers. I haven't checked recently if the ABI documentation reflects
> reality, in 10.4 days it didn't.
Thanks for the tip. I shall have to go diving into libffi to see exactly
what the rules really are then. I suspect they might be different for PPC &
Intel, because the PPC32 docs still say that only r3 is used, for a limit of
4 bytes.
sherm--
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