How do you make your UNIX crash ???

[Guy Harris]

>Awhile back, someone found that executing random data made quite
>a few RISC chips sieze up.

No, a while back, someone found that executing random data made some
operating systems running on machines with RISC chips crash, and
immediately charged ahead and, on the basis of that small bit of partial
data and a lot of assumptions about RISC chip design methodology,
speculated that this was caused by RISC-chip designers not being as
rigorous as CISC-chip designers in testing their chips.

Subsequent to this:

	1) the same program was found to crash the OS on at least one
	   machine running a *CISC* chip (a 80386 machine, I think);

	2) at least in one case, the problem was a bug in the *OS*'s
	   code to deal with, as I remember, illegal instructions in the
	   delay slots of illegal branches, or something like that (this
	   was in the MIPS version).

At some point, I may dive in and see what caused SunOS to barf; I
suspect it's a bug in the floating-point simulation code (which may get
invoked even on SPARCs with an FPU, as the FPU may not implement every
single floating-point instruction in the architecture).

If one wishes to consider the code that broke on the RISC machines to be
low-enough-level support code that it "should" be considered as much a
part of the architecture's implementation as would the chip itself, you
could, I guess, flame RISC - or, at least, the folks doing the software
part of the implementation.

Of course, given that, you can probably find plenty of microcode bugs to
damn CISC as well, if your goal is to bash some particular architecture
style (the posting in which the person revealed the results of his test
had a bit of a RISC-bashing flavor to it).

(Followups directed to "alt.religion.computers", if you really feel you
*MUST* make your 2 small monetary units worth known on the RISC vs. CISC
topic.)