gp         = buildReg("AX CX DX BX BP SI DI R8 R9 R10 R11 R12 R13 R15")
		g          = buildReg("g")
		fp         = buildReg("X0 X1 X2 X3 X4 X5 X6 X7 X8 X9 X10 X11 X12 X13 X14")
		x15        = buildReg("X15")
		gpsp       = gp | buildReg("SP")
		gpspsb     = gpsp | buildReg("SB")
		gpspsbg    = gpspsb | g
		callerSave = gp | fp | g // runtime.setg (and anything calling it) may clobber g
	)

	// going to compile.
	goFile = objdir + goFile
	newGoFile := objdir + "_" + base + "_swig.go"
	if cfg.BuildX || cfg.BuildN {
		sh.ShowCmd("", "mv %s %s", goFile, newGoFile)
	}
	if !cfg.BuildN {
		if err := os.Rename(goFile, newGoFile); err != nil {
			return "", "", err
		}
	}
	return newGoFile, objdir + gccBase + gccExt, nil
}