Re: ELF to COFF Convertor

jgj@ssd.csd.harris.com (Jeff Jackson) writes:


> > 5) V.4 uses r13 to point to the small data area, while PowerOpen uses it
> > as a normal caller save register, and NT reserves it for use by the
> > operating system. PowerOpen
>
> I'm not sure what the "small data area" is. If you mean aggregate
> return values, these are passed as a hidden first argument in
> Concurrent's implementation.


(Note, I'm using the gas syntax, since that's what I use and wrote).


A small data area points to a location in memory (+32768 from the
beginning of the .sdata sectionin the case of the Solaris/Linux
powerpc V.4/eabi). Small variables can be referenced in one
instruction:


lwz 0,foo@sdarel(13)


and the linker will automatically put the address of foo - the address
of _SDA_BASE_ into the address field. This is similar to the GP
register used in SGI/MIPS systems.


In eabi, there are two small data pointers, plus memory around
location 0 can used, and the asm looks like:


lwz 0,foo@sda21(0)


The linker then puts the appropriate register (0, 2, or 13) into the
index register field and the lower 16 bits.


--
Michael Meissner, Cygnus Solutions (East Coast)
4th floor, 955 Massachusetts Avenue, Cambridge, MA 02139, USA
meissner@cygnus.com, 617-354-5416 (office), 617-354-7161 (fax)
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