Normally, when a type 2, 3 or 4 SVC exit, the exit routine restores registers R2 through R14 from the RB. SVC 144 must be doing something weird.
-- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Discussion List <[email protected]> on behalf of Thomas David Rivers <[email protected]> Sent: Thursday, May 31, 2018 5:05 PM To: [email protected] Subject: ptrace + SVC 144 + R14 + dbx setting register values The doc on the BPX1PTR (ptrace) facility indicates that an SVC 144 should be used to set a break-point, but it very carefully then goes on to say this: Any modification that is made to register 14 with a PT_WRITE_GPR request is lost. This is because the SVC 144 routine uses register 14 to exit. which is a little surprising - because there might be really good reasons to want to change register 14 at a break-point. I tried to change $r14 in dbx at a break-pt and sure enough, couldn't do it. Then I tried setting $r0 to something - and that didn't work either... (using the dbx command: set $r0=5 for example - which got no complaints but also didn't perform the task.) I didn't find anything in the dbx documentation that says "oh - you can't set $r<n> (general register) values." So - this has led me to ask a question - can you set register values in dbx when you reach a break point? Or - is this a bug? Or - more likely - am I not doing something right? And - why would register 14 be so carefully carved-out? Seems like the SVC 144 could "return" without requiring R14, perhaps via some LOADPSW or similar approach within the bowels of the OS... Thoughts ?? - Thanks - - Dave R. - -- [email protected] Work: (919) 676-0847 Get your mainframe programming tools at http://secure-web.cisco.com/1CzGrAdWjXouncBLAMgEAPueYDApT9-f1uEuoLulXmy2splM8ZKR8OXMkqkQrbMigAXnOsCOp3rgUSrvuvWAzwY3msOgGPIHPtBFEkbXpMlWO1AneA1yUEcsP4qRLy1-W4Wy6PbMonzzeARd4hGq0NjENaiirlHgNWMxBz4dQqjDLgEi0bzml7283sIqZGZF20myW4ZlHsch57QERuTtnqqJgD-nCjuckYRlfEfEEtuK6YwCuOd8jNPHgAn8yn9H-6ct8Do2EsjSKabvOZ0m5jW_sW_loQQ-bNZsqZA709VyHKOc671p7RGJiiKlFHyx9ZxhAzTsW0I5oupDRvhNZlYdrDH7jYQhQHPH2xMc4VNJ48f0gP4W7tHFXm6c6Z37V/http%3A%2F%2Fwww.dignus.com ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
