OK, consensus seems to be that this would be unnecessary.
On Tue, 2011-12-27 at 16:08 -0600, McKown, John wrote: > I've been coding up a UNIX program in HLASM. One thing that I'm doing > is "chain chasing" using pointers. The end of chain is indicated by a > pointer of binary zeros: A(0). The code basically loops by doing an LT > instruction of the next pointer, followed by a JNZ. Works quite well. > Now my mind is churning a bit. I seen this type of thing in a lot of C > code as well. But it depends on the programmer remembering to check > the next pointer for NULL. So what occurred to me was: "Why doesn't > the hardware do this?". That spawned an idea that I would like your > feedback on. What do you think of a hardware feature, selectable via a > bit in a control register, so that addresses in "low core" can only be > referenced via GPR0? When using GPR0 as either a base or index > register, the actual contents are actually and F'0' is used as the > value. I don't know of any exception to this rule. So why not extend > it? I.e. if you use any register as a base register in an instruction, > and that register contains F'0' (or D'0' in AMODE 64) or x'80000000', > then a program interrupt occurs. Granted, this could cause a "false > positive" for those people who reverse the meaning of the "base" and > "index" registers. This could cause a "false positive". Which is why > it should be governed by a bit in a control register. Perhaps with > some way in the binder to indicate that the "interrupt if base > register contents are NULL" switch should be ON for a particular > module. I wonder if this would help with program bugs. It would > definately stop the branch to location 0 when a VCON is unsatisfied. > And the interrupt would be on the branch instruction instead of being > in low memory. > > Good idea? Or stupid? > > John McKown > Systems Engineer IV > IT > > Administrative Services Group > > HealthMarkets(r) > > 9151 Boulevard 26 * N. Richland Hills * TX 76010 > (817) 255-3225 phone * > [email protected] * www.HealthMarkets.com > > Confidentiality Notice: This e-mail message may contain confidential or > proprietary information. If you are not the intended recipient, please > contact the sender by reply e-mail and destroy all copies of the original > message. HealthMarkets(r) is the brand name for products underwritten and > issued by the insurance subsidiaries of HealthMarkets, Inc. -The Chesapeake > Life Insurance Company(r), Mid-West National Life Insurance Company of > TennesseeSM and The MEGA Life and Health Insurance Company.SM -- John McKown Maranatha! <><
