The below reply is copied from the google groups interface, looks like it was not sent to this list but just to the web interface.
On Thursday, June 20, 2019 at 11:08:16 PM UTC-4, robert...@yahoo.com wrote: > On 20 Jun 2019 06:16:47 -0700, john...@gmail.com (John > McKown) wrote: > > >This is purely speculation, but I like what I've read about the "trap" > >facility. I think it is too bad that z/OS doesn't support the use of TRAP2, > >TRAP4, as well as the compare-and-trap and load-and-trap. I agree that they > >are not _necessary_ since the code can do basically the same thing. The > >only reason that I even bring it up is that the paper "IBM Z / LinuxONE > >System Processor Optimization Primer" by C. Kevin Shum on page 51 > >"Optimization - Instruction Selection (1)" recommends using > >"compare-and-trap" where practical, in particular, for null-pointer > >checking. > > > >Perhaps I should have waited for Friday to post this since it is only > >wishful thinking. > > > Unlike the TRAP2/4 instructions, compare-and-trap and load-and-trap > generate perfectly ordinary data exception, and require no particular > support from the OS. They do set a different DXC, although ignoring > that isn't going to impact much. Yes, but that "perfectly ordinary data exception" requires quite a long code path through z/OS services to handle. That is all well and good for one-off trapped conditions, but what about (for an instance) being able to use TRAP and friends to implement instruction-level debugging software or to implement hardware instruction emulators for instruction tracing of complex programs? For such applications a much more efficient mechanism implementing TRAP processing is needed. Since the low-level TRAP interface is hardware-based it SHOULD be far more efficient to use for such purposes than depending on the existing data-exception-catching services. Of course, any formal z/OS support will likely make that reasonably efficient interface far more complicated and expensive. Just my $0.02USD worth. Peter -- This message and any attachments are intended only for the use of the addressee and may contain information that is privileged and confidential. If the reader of the message is not the intended recipient or an authorized representative of the intended recipient, you are hereby notified that any dissemination of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by e-mail and delete the message and any attachments from your system. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
