[Crash-utility] bt -f fix for s390(x)

Hi Dave, Here comes a fix for the bt -f command. The problem is that when the backchain is invalid on s390(x) we can get huge values for the stackframe size. This can lead to a termination of crash with a SIGSEGV. To fix this, we have to use in case of an invalid backchain the difference between the current backchain and the end of the stack as stackframe size. --- diff -Naur crash-4.0-2.31/s390.c crash-4.0-2.31-s390-bt-f.fix/s390.c --- crash-4.0-2.31/s390.c 2006-06-27 16:15:32.000000000 +0200 +++ crash-4.0-2.31-s390-bt-f.fix/s390.c 2006-07-03 16:37:34.000000000 +0200 @@ -714,7 +714,9 @@ frame_size = stack_base - old_backchain + KERNEL_STACK_SIZE; } else { - frame_size = backchain - old_backchain; + frame_size = MIN((backchain - old_backchain), + (stack_base - old_backchain + + KERNEL_STACK_SIZE)); } for(j=0; j< frame_size; j+=4){ if(j % 16 == 0){ diff -Naur crash-4.0-2.31/s390x.c crash-4.0-2.31-s390-bt-f.fix/s390x.c --- crash-4.0-2.31/s390x.c 2006-06-27 16:15:32.000000000 +0200 +++ crash-4.0-2.31-s390-bt-f.fix/s390x.c 2006-07-03 16:37:37.000000000 +0200 @@ -747,7 +747,9 @@ frame_size = stack_base - old_backchain + KERNEL_STACK_SIZE; } else { - frame_size = backchain - old_backchain; + frame_size = MIN((backchain - old_backchain), + (stack_base - old_backchain + + KERNEL_STACK_SIZE)); } for(j=0; j< frame_size; j+=4){ if(j % 16 == 0){