port-i386/44078: port-i386 crash to BIOS on demand from user mode SIGTRAP

[jreiser%BitWagon.com@localhost]

>Number:         44078
>Category:       port-i386
>Synopsis:       i386 crash to BIOS on demand from user mode SIGTRAP
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    port-i386-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Nov 10 16:35:00 +0000 2010
>Originator:     John Reiser
>Release:        NetBSD 5.0.2
>Organization:
BitWagon Software LLC
>Environment:
System: NetBSD NetBSD32.local 5.0.2 NetBSD 5.0.2 (GENERIC) #0: Sat Feb 6 
17:53:27 UTC 2010 
builds%b7.netbsd.org@localhost:/home/builds/ab/netbsd-5-0-2-RELEASE/i386/201002061851Z-obj/home/builds/ab/netbsd-5-0-2-RELEASE/src/sys/arch/i386/compile/GENERIC
 i386
Architecture: i386
Machine: i386 (amd64 in i386 mode)
>Description:
        Executing a 3-instruction program causes a crash to BIOS about 70%
        of the time.  The other 30% the shell reports "SIGTRAP - core dumped"
        which is correct.  Sometimes gdb catches the SIGTRAP and reports pc
        == 0x80010033 with sp==0x0, despite no pages mapped at either address.
        Machine is amd64 running in i386 mode:
        processor       : 0
        vendor_id       : AuthenticAMD
        cpu family      : 15
        model           : 15
        model name      : AMD Athlon(tm) 64 Processor 3200+
        stepping        : 2
        cpu MHz         : 2010.35
        fdiv_bug        : no
        fpu             : yes
        fpu_exception   : yes
        cpuid level     : 1
        wp              : yes
        flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge 
mca cmov pat pse36 clflush mmx fxsr sse sse2 

>How-To-Repeat:
----- file nop.S
_start: .globl _start
        nop
        int3
        nop
-----
$ gcc -o nop -nostartfiles -nostdlib nop.S
$ ./nop
>Fix: