[Bug 255191] Booting DragonFlyBSD results in Failed to emulate instruction sequence output

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=255191

Peter Grehan <grehan at FreeBSD.org> changed:

           What    |Removed                     |Added
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                 CC|                            |grehan at FreeBSD.org

--- Comment #3 from Peter Grehan <grehan at FreeBSD.org> ---
I looked into this a while back: there are 2 issues
 - DFly is accessing memory beyond 4G when there is < 4G configured. This
appears to be an array access in
sys/platform/pc64/x86_64/mptable.c:mptable_search_sig()
   However, in PC-land this is allowed and accesses beyond the end of RAM will
return 0xff's on a read.

 - bhyve does return 0xff's for reads beyond the end of memory, but doesn't
implement that particular instruction (cmpl   $0x5f504d5f,(%rax,%rcx,4))

Rather than having to implement that instruction for such an edge condition,
I'll try and resurrect the patch I once had (unfortunately lost) and get the
fix into DFly.

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