[Bug 1892540] Re: qemu can no longer boot NetBSD/sparc

[Laurent Vivier]

This happens because openbios accesses unassigned memory during the SBus
scan:

Probing SBus slot 0 offset 0
invalid accepts: (null)  addr 20000000 size: 1
Probing SBus slot 1 offset 0
invalid accepts: (null)  addr 30000000 size: 1
Probing SBus slot 2 offset 0
invalid accepts: (null)  addr 40000000 size: 1
Probing SBus slot 3 offset 0
Probing SBus slot 4 offset 0
invalid accepts: (null)  addr 60000000 size: 1
Probing SBus slot 5 offset 0

Thread 4 "qemu-system-spa" hit Breakpoint 1, memory_region_access_valid 
(mr=0x555555df20c0 <io_mem_unassigned>, 
    addr=536870912, size=1, is_write=<optimized out>, attrs=...)
    at .../softmmu/memory.c:1358
1358            return false;

(gdb) list

1355        if (mr->ops->valid.accepts
1356            && !mr->ops->valid.accepts(mr->opaque, addr, size, is_write, 
attrs)) {
1357            fprintf(stderr, "invalid accepts: %s  addr %"PRIx64 " size: 
%d\n", mr->name, addr, size);
1358            return false;
1359        }

(gdb) p mr->ops->valid.accepts
$1 = (_Bool (*)(void *, hwaddr, unsigned int, _Bool, MemTxAttrs)) 
0x555555736f10 <unassigned_mem_accepts>

(gdb) list unassigned_mem_accepts
1271
1272    static bool unassigned_mem_accepts(void *opaque, hwaddr addr,
1273                                       unsigned size, bool is_write,
1274                                       MemTxAttrs attrs)
1275    {
1276        return false;
1277    }

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https://bugs.launchpad.net/bugs/1892540

Title:
  qemu can no longer boot NetBSD/sparc

Status in QEMU:
  New

Bug description:
  Booting NetBSD/sparc in qemu no longer works.  It broke between qemu
  version 5.0.0 and 5.1.0, and a bisection identified the following as
  the offending commit:

    [5d971f9e672507210e77d020d89e0e89165c8fc9] memory: Revert "memory:
  accept mismatching sizes in memory_region_access_valid"

  It's still broken as of 7fd51e68c34fcefdb4d6fd646ed3346f780f89f4.

  To reproduce, run

    wget http://ftp.netbsd.org/pub/NetBSD/NetBSD-9.0/images/NetBSD-9.0-sparc.iso
    qemu-system-sparc -nographic -cdrom NetBSD-9.0-sparc.iso -boot d

  The expected behavior is that the guest boots to the prompt

    Installation medium to load the additional utilities from:

  The observed behavior is a panic:

    [   1.0000050] system[0]: trap 0x29: pc=0xf0046b14 sfsr=0xb6 sfva=0x54000000
    [   1.0000050] cpu0: data fault: pc=0xf0046b14 addr=0x54000000 
sfsr=0xb6<PERR=0x0,LVL=0x0,AT=0x5,FT=0x5,FAV,OW>
    [   1.0000050] panic: kernel fault
    [   1.0000050] halted

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