So, you will have a load module marked AM32. All instructions use only the lower half of the registers, no grande or high portion instructions. The program loader gets memory at x'0000 0000 80000 0000' (or the next location not in use) and loads your program, sets AM64 and calls your entry point. Any interrupts or calls save all 64 bits and when your program is resumed all 64 bits until it exits. Should work just fine if the starting address is x'0000 0001 0000 0000' or x'0000 0002 0000 0000' since all calls should be in the 4GiB area. Any instruction that loads an address into a register is controlled by the AMODE.
On Sun, May 6, 2018 at 5:15 PM, Paul Edwards <[email protected]> wrote: > On Sun, 6 May 2018 15:08:24 -0700, Charles Mills <[email protected]> wrote: > >>What exactly would the benefit be? > > Any 32-bit program currently coming up > against the 2 GiB barrier can have its life > extended by bumping the limit up to 4 GiB. > >> Currently, if one wants to address more than >> 2GiB of memory one has to be a full AMODE 64 >> program. > > Executing in AMODE 64 is fine. Rewriting a > 32-bit program to be 64-bit, using 64-bit > data pointers, is *not*. > >> This would let a program address 4GiB while only >> using 32-bit registers and addresses in storage -- >> is that the point? > > Yes, this is the point. > >> Or am I confused? Is that the whole point? > > The point is that 32-bit programs can access > 4 GiB of memory as programmers would > normally hope is possible. > >> If so, I see the benefit, but not the benefit to >> effort ratio. > > What effort? Depending on how the existing > 32-bit code is written, all you need to do is > change a LOC=31 to LOC=32. > >> Or putting it differently, aren't three addressing >> modes enough for a system service to have to >> deal with? > > 3 is fine. I'm not asking for a new addressing > mode. AM64 is fine. So long as the top 32 > bits of 64-bit registers remain as zero (a 32-bit > program is never going to change that), AM64 > is just as good as an AM32, so there's no need > to create an AM32, so there's very little effort > involved. > > BFN. Paul. > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to [email protected] with the message: INFO IBM-MAIN -- Mike A Schwab, Springfield IL USA Where do Forest Rangers go to get away from it all? ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
