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Date: Wed, 06 Aug 2014 10:12:06 -0400
From: Eric van Gyzen <eric@vangyzen.net>
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Subject: Sanity Check:  Bogus(?) General Protection Fault
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Can someone give me a quick sanity check?  I'm debugging a General
Protection Fault on an amd64 system.  The faulting instruction appears
to be an immediate mov into %r11...right?  I ask because I can't imagine
how that instruction could cause a GPF.  Any ideas?

Thanks,

Eric

====

Fatal trap 9: general protection fault while in kernel mode
cpuid = 0; apic id = 00
instruction pointer     = 0x20:0xffffffff805d6e23
stack pointer           = 0x28:0xfffffe0463d45660
frame pointer           = 0x28:0xfffffe0463d456d0
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0


db> bt
Tracing pid 1017 tid 100169 td 0xfffff801d4500000
vm_reserv_alloc_contig() at vm_reserv_alloc_contig+0x3b3/frame
0xfffffe0463d456d0
vm_page_alloc_contig() at vm_page_alloc_contig+0x13b/frame
0xfffffe0463d45760
kmem_alloc_contig() at kmem_alloc_contig+0x12f/frame 0xfffffe0463d45810
contigmalloc() at contigmalloc+0x33/frame 0xfffffe0463d45850
[snip]


0xffffffff805d6e0f <vm_reserv_alloc_contig+927>:    mov    0x30(%rax),%r9
0xffffffff805d6e13 <vm_reserv_alloc_contig+931>:    shr    $0x15,%r9
0xffffffff805d6e17 <vm_reserv_alloc_contig+935>:    shl    $0x6,%r9
0xffffffff805d6e1b <vm_reserv_alloc_contig+939>:    mov  
 0xffffffff809bf7a8,%r11
0xffffffff805d6e23 <vm_reserv_alloc_contig+947>:    mov  
 %rcx,0x10(%r11,%r9,1)