Add missing .register declarations.
Load the saved callback data from the stack into %g5, see the
  trampoline.c patch for more info.
Initalize __va_alist->anum to 0.

--- callback/vacall_r/vacall-sparc64.S.orig	Fri Nov 26 12:35:23 1999
+++ callback/vacall_r/vacall-sparc64.S	Sat Apr 25 13:58:31 2009
@@ -4,10 +4,14 @@
 .section	".text"
 	.align 4
 	.global __vacall_r
+	.register %g2, #scratch
+	.register %g3, #scratch
 	DECLARE_FUNCTION(__vacall_r)
 	.type	 __vacall_r,$function
 	.proc	020
 __vacall_r:
+	ldx	[%sp+2239], %g5
+	add	%sp, 32, %sp
 	!$PROLOGUE$ 0
 	save	%sp, -448, %sp
 	!$PROLOGUE$ 1
@@ -55,6 +59,7 @@ __vacall_r:
 	st	%f31, [%fp+1895]
 	st	%g0, [%fp+1775]
 	stx	%g0, [%fp+1791]
+	st	%g0, [%fp+1831]
 	st	%g0, [%fp+1799]
 	ldx	[%g5], %o2
 	call	%o2, 0