panic with 'vmstat -e' on -current kernel with 9.1 userland

[Jared McNeill <jmcneill%invisible.ca@localhost>]

I hit this panic (repeatable 100%) trying to run 'vmstat -e' with a 
-current kernel and 9.1 userland:

[  78.8000072] panic: Trap: Data Abort (EL1): Translation Fault L1 with read access for 0000000000000000, PAN Set: pc ffffc00000806d68: ldrb w2, [x1]

[  78.8104731] cpu0: Begin traceback...
[  78.8104731] trace fp ffffc0004c767720
[  78.8104731] fp ffffc0004c767750 vpanic() at ffffc000004e3b0c netbsd:vpanic+0x14c
[  78.8104731] fp ffffc0004c7677b0 panic() at ffffc000004e3c04 netbsd:panic+0x44
[  78.8104731] fp ffffc0004c767840 data_abort_handler() at ffffc00000090d8c netbsd:data_abort_handler+0x1ec
[  78.8104731] tf ffffc0004c7678b0 el1_trap() at ffffc00000092784 netbsd:el1_trap
[  78.8104731] ---- trapframe 0xffffc0004c7678b0 (304 bytes) ----
[  78.8104731]     pc=ffffc00000806d68,   spsr=0000000060400005
[  78.8104731]    esr=0000000096000005,    far=0000000000000000
[  78.8104731]     x0=ffff00005de9a11c,     x1=0000000000000000
[  78.8104731]     x2=ffff00005de9a11c,     x3=0000000000000003
[  78.8206028]     x4=000000000000000f,     x5=0000000000000000
[  78.8206028]     x6=0000000000000000,     x7=000000000000002f
[  78.8206028]     x8=ffff00005b3b6400,     x9=0000000000000001
[  78.8206028]    x10=ffff00005593f900,    x11=000000000000003f
[  78.8206028]    x12=fffffc000177a684,    x13=fffffc000177a68c
[  78.8206028]    x14=00000000000003bd,    x15=ffff00005de9a320
[  78.8206028]    x16=0000f27a428708b0,    x17=0000f27a428089e4
[  78.8206028]    x18=0000000000000000,    x19=000000000000000b
[  78.8206028]    x20=00000000ffffffff,    x21=00000000000009a0
[  78.8206028]    x22=00000000000008a0,    x23=0000f27a42ab8970
[  78.8206028]    x24=ffffc000011a9780,    x25=0000000000000001
[  78.8206028]    x26=ffffc000037baaf0,    x27=0000000000000030
[  78.8206028]    x28=ffff00005de9a100, fp=x29=ffffc0004c767be0
[  78.8305824] lr=x30=ffffc000004d0da8,     sp=ffffc0004c767be0
[  78.8305824] ------------------------------------------------
[  78.8305824] fp ffffc0004c767be0 strcpy() at ffffc00000806d68 netbsd:strcpy+0x8
[  78.8305824] fp ffffc0004c767c00 sysctl_doevcnt() at ffffc000004d0da4 netbsd:sysctl_doevcnt+0x13c
[  78.8305824] fp ffffc0004c767cc0 sysctl_dispatch() at ffffc000004b6ff4 netbsd:sysctl_dispatch+0xb4
[  78.8305824] fp ffffc0004c767d30 sys___sysctl() at ffffc000004b7248 netbsd:sys___sysctl+0xb0
[  78.8305824] fp ffffc0004c767db0 syscall() at ffffc0000008ed94 netbsd:syscall+0x18c
[  78.8305824] fp ffffc0004c767e60 trap_el0_sync() at ffffc00000090240 netbsd:trap_el0_sync+0x378
[  78.8407101] tf ffffc0004c767ed0 el0_trap() at ffffc000000927f0 netbsd:el0_trap
[  78.8407101] ---- trapframe 0xffffc0004c767ed0 (304 bytes) ----
[  78.8407101]     pc=0000f27a428089e8,   spsr=0000000080000000
[  78.8407101]    esr=00000000560000ca,    far=0000f27a4273ca10
[  78.8407101]     x0=0000ffffffbfb440,     x1=0000000000000004
[  78.8407101]     x2=0000f27a42ab8000,     x3=0000ffffffbfb540
[  78.8407101]     x4=0000000000000000,     x5=0000000000000000
[  78.8407101]     x6=0000000000002220,     x7=0000000000000001
[  78.8407101]     x8=0000f27a42885e40,     x9=00000000000003e4
[  78.8407101]    x10=0000000000000000,    x11=000000700874f000
[  78.8407101]    x12=0000f27a42ac53e8,    x13=000000000000001d
[  78.8407101]    x14=00000000000003bd,    x15=0000f27a42202768
[  78.8407101]    x16=0000f27a428708b0,    x17=0000f27a428089e4
[  78.8510494]    x18=0000000000000000,    x19=0000f27a4286f000
[  78.8510494]    x20=0000f27a42ab8000,    x21=00000000ffffffff
[  78.8510494]    x22=000000000000004f,    x23=0000000000001210
[  78.8510494]    x24=000000020011a000,    x25=0000000000000000
[  78.8510494]    x26=0000000000000000,    x27=000000020011aca8
[  78.8510494]    x28=0000000000000000, fp=x29=0000ffffffbfb220
[  78.8510494] lr=x30=0000f27a428084dc,     sp=0000ffffffbfb220
[  78.8510494] ------------------------------------------------
[  78.8510494] cpu0: End traceback...

[  78.8510494] dump to dev 92,33 not possible
[  78.8775739] rebooting...