On Wed, Jun 20, 2018 at 8:59 AM Don Poitras <poit...@pobox.com> wrote:
> In article <CAAJSdjjjH6CZfpbbKdJCZbKnj0A9bjypHoOPqfAcfTyJ4_= > u...@mail.gmail.com> you wrote: > > On Tue, Jun 19, 2018 at 3:18 PM Farley, Peter x23353 < > > peter.far...@broadridge.com> wrote: > > > The recent discussion about the ability (or not) of setting R14 values > in > > > dbx at a break point while debugging brought me back to an old and > (for me) > > > somewhat sore subject. > > > > > > The z/Architecture hardware designers graced us with TRAP and TRAP4 and > > > then with compare-and-trap instructions in the hardware. > > > > > > z/OS has yet to provide ordinary application-mode programmers (or for > that > > > matter compiler and debugger writers) with the tools to use these > hardware > > > features. Because updates to the DUCT are needed to properly utilize > the > > > TRAP features, only supervisor-state code (and therefore only > > > APF-authorized code) can use these facilities in current z/OS versions, > > > leaving ordinary application programmers with no way to use any of > these > > > hardware features.. > > > > > > When will z/OS provide application programmers (and others) the tools > to > > > utilize TRAP and friends? > > > > > > Inquiring minds would love to know. > > > > > ???I totally agree. This would make it easy to "trap" a C language style > > "null pointer" dereferencing. A simple " CIT Rn,0,0" after doing a load > of > > the pointer. Or, after looking, a LAT or LGAT, which does an automatic > > compare against 0, would make the C language much safer! All at "no cost" > > to the compiler writers. However, this is assuming that the use of the > TRAP > > facility is relatively "cost free". I know that in the past, the SLIP IF > > function was strongly discouraged because it use PER (Program Event > > Recording?) which caused _significant_ CPU overhead. But that was back in > > the 3090 days. I don't know as much about the z13+ internals. In fact, > > perhaps CPU/performance impact is the reason that IBM doesn't make this > > GUPI. Because GUPI implies "yes, feel free to use this anywhere you think > > it makes sense" and if you get a 20% CPU hit, people will respond by > > hitting back. > > > > > > Peter > > > > > -- > > There is no such thing as the Cloud. It is just somebody else???s > computer. > > Maranatha! <>< > > John McKown > > You'd also want to have some language feature that _wouldn't_ trap if > you _intend_ to do a "null pointer" dereference. After all, the first > page of memory is where lots of good stuff lives. :) > True. I guess that it would be helpful to have compile option to "globally" enable or disable this ability. Along with a #pragma to turn this particular code generation option on & off "in line" as required. Another, worse?, option would be a C language modifier similar to __volatile__ declaration modifier. Or maybe a suboption to __attribute__. > > Also, I'm not sure how widely this is used, but we've gotten a lot of use > out of it. "SLIP zero address detection (ZAD)" > > > https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.3.0/com.ibm.zos.v2r3.ieag100/zaduse.htm > > -- > Don Poitras - SAS Development - SAS Institute Inc. - SAS Campus Drive > sas...@sas.com (919) 531-5637 Cary, NC 27513 > -- There is no such thing as the Cloud. It is just somebody else’s computer. Maranatha! <>< John McKown ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
