port-xen/41401: pthreaded apps crash i386/xen kernel

[jakllsch%kollasch.net@localhost]

>Number:         41401
>Category:       port-xen
>Synopsis:       pthreaded apps crash i386/xen kernel
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    port-xen-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun May 10 14:20:01 +0000 2009
>Originator:     Jonathan A. Kollasch
>Release:        NetBSD 5.99.11 20090509
>Organization:
        
>Environment:
Architecture: i386
Machine: i386
>Description:

x86_set_sdbase() tries to directly write to the GDT, which isn't directly 
accesible in the xen case.

dhcpcd - - - xennet0: leased 172.27.42.245 for 86400 seconds
uvm_fault(0xc03e21c0, 0xc4a57000, 2) -> 0xe
fatal page fault in supervisor mode
trap type 6 code 3 eip c02aee73 cs 9 eflags 10282 cr2 c4a570b0 ilevel 0
kernel: supervisor trap page fault, code=0
Stopped in pid 348.1 (dig) at   netbsd:x86_set_sdbase+0xb7:     movl    
%edx,0(%eax)
db> bt
x86_set_sdbase(bfa00000,67,c57db820,1,0,1000,c591dcdc,c02aeab4,c57db820,bfa00000)
 at netbsd:x86_set_sdbase+0xb7
cpu_lwp_setprivate(c57db820,bfa00000,c57cb598,0,c03a8c98,c57db820,c591dd3c,c02b6115,c57db820,c591dd00)
 at netbsd:cpu_lwp_setprivate+0x15
sys__lwp_setprivate(c57db820,c591dd00,c591dd28,c591dd00,bfa00000,c57cb598,13d,bfa00000,1c,bfbfeb90)
 at netbsd:sys__lwp_setprivate+0x1c
syscall(c591dd48,1f,1f,1f,1f,1c,bfa00000,bfbfeb90,bba5b24c,0) at 
netbsd:syscall+0xf5
db>

the failing line is sys/arch/x86/x86/sys_machdep.c:1.18:628.

>How-To-Repeat:
boot a i386 XEN3 kernel, run dig, or try to build perl

>Fix:
maybe not try to modify the gdt on xen?