Sender:	nate AT cartsys DOT com
Message-ID:	<35EB46EF.911D60A5@cartsys.com>
Date:	Mon, 31 Aug 1998 17:59:27 -0700
From:	Nate Eldredge <nate AT cartsys DOT com>
MIME-Version:	1.0
To:	GAMMELJL AT SLU DOT EDU
CC:	djgpp AT delorie DOT com
Subject:	Re: passing arguments in registers
References:	<01J19GJU8Q9U94JXNE AT SLU DOT EDU>

GAMMELJL AT SLU DOT EDU wrote:
> 
> The following C/C++ code when compiled:
>                 gxx example9.cc -S -O2
> results in the .s file below it.  It is plain that the arguments
> of zadd are passed on the stack.  Eli Zareteskii has told me that
> passing them in registers requires
>                  __attribute__((regparm=2))
> and that the information about this is in the GCC docs.  Please:
> someone expert in searching these docs tell me exactly where this
> attribute statement goes in the C++ code below and exactly what the
> correct syntax is.

>From GCC Manual, node "Function Attributes":

#    The keyword `__attribute__' allows you to specify special
attributes
# when making a declaration.  This keyword is followed by an attribute
# specification inside double parentheses. 
...
# `regparm (NUMBER)'
#      On the Intel 386, the `regparm' attribute causes the compiler to
#      pass up to NUMBER integer arguments in registers EAX, EDX, and
ECX
#      instead of on the stack.  Functions that take a variable number
of
#      arguments will continue to be passed all of their arguments on
the
#      stack.

So:

extern int zadd(int m, int n) __attribute__((regparm(2)));

Make sure this prototype is in scope when you define `zadd'!

(I added the explicit `int').
-- 

Nate Eldredge
nate AT cartsys DOT com

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