Autzoo.879 net.v7bugs utzoo!henry Tue Aug 11 19:17:02 1981 non-I/D floating-point Mike Tilson of Human Computing Resources has uncovered a fairly serious bug in the machine-language assist for non-I/D machines. The code tests to see whether the machine has hardware floating-point, and sets the variable "fpp" appropriately; said variable is consulted at context-switch time to determine whether floating-point registers should be saved and restored. But in the version of this code for non-I/D machines, fpp is set just before the clearing of the kernel bss -- and fpp is IN THE BSS! Hence, on a non-I/D machine, fpp is always 0, floating-point registers are NEVER saved/restored, and if the machine has floating-point hardware and more than one process is trying to use it, chaos and madness will ensue. Fix is to move the six lines of code starting "/ test for floating point" and ending "clr nofault", at about line 55 of /usr/sys/40/m40.s, to just after the clearing of the bss (i.e. to about line 69). This bug is present in both the Bell m40.s and the Dec-Merrimack mch_i.s . The I/D versions get things right in both cases.