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From: steve@maths.warwick.ac.uk (Steve Rumsby)
Newsgroups: comp.lang.c++
Subject: Re: stdarg on sparc
Message-ID: <2030@diamond.warwick.ac.uk>
Date: 12 Dec 89 16:33:42 GMT
Sender: news@warwick.ac.uk
Reply-To: steve@maths.warwick.ac.uk (Steve Rumsby)
Organization: Mathematics Institute, University of Warwick, UK.
Lines: 91


Yes, it's possible to make it work. There are two things you need to do,
one to the code itself, and one to the CC script (or to the output of
CC -Fc before feeding to cc itself if you can't hack CC).

1) To the code using stdargs:

First, add this to the beginning, or in a header file that you include,
or somewhere:

#ifdef	sparc
#define	SA(x)	__builtin_va_alist
#else
#define	SA(x)	x
#endif

Then change code like this:

void
foo(int x, char *p, ...)
{
	va_list ap;

	if(!p)
		return;

	va_start(ap, p);

	[...etc...]
}

To this:

void
foo(int x, char *SA(p), ...)
{
	va_list ap;

	if(!SA(p))
		return;

	va_start(ap, SA(p));

	[...etc...]
}

ie. change ALL occurances of the last named argument to SA(name).

2) Changes to CC itself:
   Cfront in going to mangle the __builtin_va_alist parameter name, so
   we need to unmangle it again so that the C compiler gets to see it.
   Do this to the output of cfront:

	sed -e 's/__0__builtin_va_alist/__builtin_va_alist/g'

   You can either do this in the CC script by changing all occurances of
   "cfront" to "cfront | sed", or you can do it to the output of CC -Fc
   and feed it to cc manually. This sed script can obviously be generalised
   to unmangle a larger set of identifiers (like all __builtin ones) if
   necessary (eg. to use gcc instead of cc as the C compiler).

Voila! You now have stdargs working on a sparc machine.

Note that there is a slightly more complex usage of stdargs in C++ which
breaks the above system. This is where arguments after the last named one
have default values, like so:

extern void foo(int, char *, int = 2, ...);

void
foo(int x, char *p, int, ...)
{
	va_list ap;

	va_start(ap, p);
}

[Is this legal? I found it in ET++]

Cfront will make up names for the unnamed arguments, and the Sun C compiler
complains about arguments after __builtin_va_alist. To make this work you
need to rip out these extra arguments (I don't understand why cfront puts them
there in the first place, actually). This is somewhat more difficult, but
not impossible. I haven't got around to fixing this yet...

					Hope all this helps,
					  Steve.


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