Re: [Libreoffice] Different x86 ABI on BSDs and MaxOSX

Hi Caolan,

On 2010-12-09 at 09:43 +0000, Caolán McNamara wrote:

> > and from what I see on page 19, it seems to me that *BSD defaults to the
> > 'fastcall' variant, right?  
>
> We're looking at "Table 7. Methods for returning structure, class and
> union objects" right ? 
>
> > The table suggests that the small structs that combine int and float
> > are returned on stack
>
> Are you looking at "Table 6. Methods for passing structure..." ? I'm
> only looking at structure *returns*.

Yeah, sorry; I knew I should have been looking at the table 7, but was
not careful, and looked at 6 :-(

> calling_conventions.pdf baffles me a little in Table 7 anyway. System V
> Application Binary Interface (abi386-4.pdf) clearly says "If a function
> returns a structure or union, then the caller provides space for the
> return value and places its address on the stack as argument word zero",
> i.e. default Linux ABI x86 does not return structs in registers, despite
> the "I" in "simple structure, class or union" for "Gnu except Mac OS"
> where I is "Returned in integer registers". We clearly don't don't
> return small structs in regs on x86 Linux so I don't know what "Gnu
> except Mac OS" refers to there.
>
> Anyway, better info where Apple documents the diff they use on MacOSX
> from the classic SYSV ABI.
>
> http://developer.apple.com/library/mac/#documentation/DeveloperTools/Conceptual/LowLevelABI/130-IA-32_Function_Calling_Conventions/IA32.html#//apple_ref/doc/uid/TP40002492-SW4

This was actually why I was looking at other sources too - thanks to the
circular dependency 'See “Returning Results” for more information.' and
'See “Passing Arguments” for more information.', I was afraid there's
missing something there :-)

> Anyway, what I'll simply do is first add some tests to testtools for
> returning something comprised of two floats, and or something comprised
> of an integer + float and for something that is 3 bytes in size, etc to
> force clarification in practice.

Thank you - and sorry for the nitpicking.

Regards,
Kendy