[Bug 811683] Re: 7400, 7410, 7450 cpus vector have wrong exception prefix at reset

[till]

I no longer have the test readily available. So I tried to print the
initial MSR and IP register contents from the QEMU monitor:

qemu-system-ppc -machine none -cpu 7400 -S -monitor stdio
QEMU 5.0.93 monitor - type 'help' for more information
(qemu) info registers
NIP 00000000   LR 00000000 CTR 00000000 XER 00000000 CPU#0
MSR 00000000 HID0 00000000  HF 00000000 iidx 0 didx 0
Segmentation fault (core dumped)

Unfortunately this lets qemu (tried 2.11.1(Debian 1:2.11+dfsg-
1ubuntu7.29) as well as 5.1.0-rc3) segfault; apparently the time-base is
not initialized but still accessed when -machine == none. Yet another
bug, it seems. The NIP and MSR seem wrong, however.

I can generate an empty ppc_rom.bin and fool a prep machine under
2.11.1:

till@tillp1  $ ls -l empty.bin
-rw-r--r-- 1 till till 0 Aug  8 12:03 empty.bin

till@tillp1  $ qemu-system-ppc -bios ./empty.bin -cpu 7400 -machine prep -S 
-monitor stdio
QEMU 2.11.1 monitor - type 'help' for more information
(qemu) info registers
NIP fff00100   LR 00000000 CTR 00000000 XER 00000000 CPU#0
MSR 00000040 HID0 00000000  HF 00000000 iidx 3 didx 3

Here, the issue is fixed! Apparently it is fixed for the 'prep' machine
but not 'none'. Unfortunately 'prep' is gone from 5.3.0 and 'none' is
buggy; wait - it seems I can emulate 'prep' with '40p':

till@tillp1  $ build/ppc-softmmu/qemu-system-ppc -machine 40p -cpu 7400 -S 
-monitor stdio
QEMU 5.0.93 monitor - type 'help' for more information
(qemu) info registers
NIP fff00100   LR 00000000 CTR 00000000 XER 00000000 CPU#0
MSR 00000040 HID0 00000000  HF 00000000 iidx 3 didx 3

This looks good, so I suppose it is OK to close this bug.

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https://bugs.launchpad.net/bugs/811683

Title:
  7400,7410,7450 cpus vector have wrong exception prefix at reset

Status in QEMU:
  Incomplete

Bug description:
  I have a proprietary ROM implementing system calls that are executed
  via the 'SC' instruction.

  I use qemu-0.14.1,

  qemu-system-ppc -M prep -cpu $CPU -bios my_bios -kernel my_kernel

  That works fine on a 604 (CPU=0x00040103) - but does not on an emulated 7400 
(CPU=0x000c0209) or 7450 (CPU=0x80000201). I found that the emulator jumps to 
0x00000c00 instead of 0xfff00c00.
  Probably this is due to a wrong setting in target-ppc/translate_init.c:

  init_excp_604() correctly sets env->hreset_vector=0xfff00000UL;

  but

  init_excp_7400() says env->hreset_vector=0x00000000UL;

  which seems wrong. (the 7400 manual says a hard-reset jumps initializes the
  prefix to 0xfff00000.)

  Likewise, init_excp_7450() (and probably other, related CPUs) are
  wrong.

  Indeed, when I change the value in init_excp_7400() to 0xfff00000UL then
  everything works as expected for me.

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