Index: linux-2.6.16-mcr/arch/powerpc/kernel/signal_64.c
===================================================================
--- linux-2.6.16-mcr.orig/arch/powerpc/kernel/signal_64.c	2006-03-27 11:09:02.000000000 +0200
+++ linux-2.6.16-mcr/arch/powerpc/kernel/signal_64.c	2006-03-27 11:14:16.986879573 +0200
@@ -213,7 +213,7 @@
         /* Default to using normal stack */
         newsp = regs->gpr[1];
 
-	if (ka->sa.sa_flags & SA_ONSTACK) {
+	if ((ka->sa.sa_flags & SA_ONSTACK) && current->sas_ss_size) {
 		if (! on_sig_stack(regs->gpr[1]))
 			newsp = (current->sas_ss_sp + current->sas_ss_size);
 	}