Ref: Your note of Wed, 26 Jun 2019 09:43:30 -0400 If you have the linkage stack available and storage containing the information needed to resume (such as an SDWA or copy) then I think it is possible to create code to resume (at least in problem state) at a chosen address with all registers containing their original values, original PSW ASC mode, AMODE, condition code and program mask, using BAKR and PR.
I originally wrote some code like this in the 1990s to implement a sort of problem-state "must complete" where the original code could be resumed for a few instructions from the recovery routine, and when it turned off "must complete" it would return control to the recovery routine. However, it was never used in production, and I'm not sure whether it was even tested, so this method comes with no guarantees. Basically, you set up the registers that are returned by PR, put the resume address in a register that isn't returned by PR, issue BAKR to save the resume address, restore the other registers and issue PR to resume. However, if you want to do it properly with condition code, ASC mode and so on, it's quite tricky. - Start in primary mode with R1 pointing to the SDWA. - Load access registers 2 through 14 (using one of the other registers to address that SDWA section). - Load general registers R2 through R14. - Get the program mask (with CC) and ASC mode in R15. - Get the PSW address and AMODE indicator bits in R0 (because R1 and R15 are still needed). - Use SAC to set the ASC mode and SPM to set program mask. - Copy the PSW instruction address and AMODE from R0 to R15. - Issue BAKR R15,0 to stack the PSW and registers R2 to R14. - Switch back to primary mode to access SDWA again. - Get the program mask again in R15. - Repeat the SPM in case PR doesn't restore the condition code (it is undefined whether PR restores the condition code, but it seems reasonable to assume it either takes the stacked one or preserves the current one). - Load access registers 15 through 1 from the SDWA, using some other register to address the relevant part. - Load general registers R15 through R1. - Issue PR to resume execution with original state restored. I hope I've remembered that correctly! I probably have some code around somewhere to do that, but I can't remember where. Jonathan Scott, HLASM IBM Hursley, UK
