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From: leech@alanine.cs.unc.edu
Newsgroups: comp.lang.c++
Subject: C++ on DECstation 3100
Message-ID: <7864@thorin.cs.unc.edu>
Date: 20 Apr 89 21:17:10 GMT
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Reply-To: leech@alanine.cs.unc.edu ()
Organization: University Of North Carolina, Chapel Hill
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    I just finished porting cfront 1.2.1 to our new DECstation 3100s
(MIPS CPU). This was a relatively easy port. The size/alignment file
is exactly the same as a Sun-4.  The only caveat is the treatment of
functions using <varargs.h>.  As usual for non-stack oriented
machines, there is magic in the C compiler which recognizes varadic
functions and generates different code sequences.  In this case, the
name 'va_alist' is recognized.	Since cfront trashes this name, it
must be restored in the intermediate C source before compiling.

    The only place this problem affects cfront directly is in
lib/stream/out.c:form().  First, form() must be modified to use
<varargs.h>.  Here's how this looks in our source:

	#if dgux | mips     /* form() requires varargs on some machines */
	#include <varargs.h>

	char *form(va_alist)
	va_dcl
	{
		char *format;
		register char* buf = bfree;
		if (max < buf+fld_size) buf = formbuf;

		va_list  args;
		va_start(args);
		format = va_arg(args, char *);
		register ll = vsprintf(buf, format, args);
		va_end(args);

		if (0<ll && ll<cb_size)				// length
			;
		else if (buf<(char*)ll && (char*)ll<buf+cb_size)// pointer to trailing 0
			ll = (char*)ll - buf;
		else
			ll = strlen(buf);
		if (fld_size < ll) exit(10);
		bfree = buf+ll+1;
		return buf;
	}
	#else
	// form() supplied with cfront goes here. Not included in this posting.
	#endif

    Second, the following patch should be made to lib/mk/makefile:
replace the standard actions for compiling out.c with

	# Kludged for DECstation 3100s (MIPS) so varargs works
	# MIPS compiler recognizes 'va_alist' and generates magic code
	#	 $(CC) $(CCFLAGS) -I../stream -c ../stream/out.c
	out.o:	../stream/out.c
		$(CC) $(CCFLAGS) -I../stream -Fc ../stream/out.c > out.c
		sed -e 's/_au0_va_alist/va_alist/g' < out.c > out..c
		cc -c out..c
		mv out..o out.o

    Similar code will be required for any user function using varargs.
Ideally, this patch would be made to the compiler, but this suffices
to get cfront & libC running.
--
    Jon Leech (leech@cs.unc.edu)    __@/
    "A compact set can be controlled by a finite police force no
     matter how dumb." H. Weyl ca. 1938