Re: rs6000 struct returns

[Michael Meissner <meissner at cygnus dot com>]

On Mon, Mar 19, 2001 at 05:48:03PM -0800, Geoff Keating wrote:
> "James L. Dein" <jdein@windriver.com> writes:
> 
> > According to the SVR4 ABI for rs6000, which is subsumed by the EABI, small 
> > structs should be returned in r3/r4, if they fit.  However, gcc is not doing 
> > that: instead, all structs are being returned just like large structs, i.e., via 
> > a secret pointer arg to an area allocated by the caller.
> > 
> > Can anyone suggest how to implement the correct behavior?  It appears that 
> > returning structs in single regs is easy to implement, but there is no support 
> > for returning in more than one reg.
> 
> Have you tried -mcall-solaris?  That should add this behaviour,
> although that's straight SVR4 not EABI.
> 
> For EABI, this is probably a straight bug.  Look at RETURN_IN_MEMORY
> in rs6000.c.  The gotcha is that this can't immediately be changed for
> linux; it's on my to-do-when-next-breaking-abi list.

Yeah, its been a bug for 5 years ago, and as Geoff mentions, fixing it will
break linking objects compiled with previous compilers (particularly the dbm_*
functions under Linux).  As I recall, structure returns is the one thing that
is different on Solaris than System V (of course PowerPC Solaris is long since
dead).

-- 
Michael Meissner, Red Hat, Inc.  (GCC group)
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