Where is that trap coming from?

[Emmanuel Dreyfus <manu%netbsd.org@localhost>]

Hello     

I am still working on LTFS, and during a dump to the tape, the
ltfs process got a SIGSEGV. crash(8) tells me that one of its thread 
has this kernel backtracee:

db{0}>  bt/a cc1d2aa0
trace: pid 5109 lid 3 at 0xdd696e9c 
sigswitch(0,b,1,c112be2c,ffffffff,c7c59dd0,c7c59f08,0,cc1d2c58,cc1d2c58) at
+netbsd:sigswitch+0xa5
issignal(cc1d2aa0,0,400,0,caa745c8,dd696f54,c7c59df4,cc1d2aa0,dd696fa8,104) at
+netbsd:issignal+0x1fc
lwp_userret(cc1d2aa0,dd696f54,dd694000,b52220e0,c,91093,c6027b2c,0,c131ec40,dd69
+6f60) at netbsd:lwp_userret+0x1c3
trap() at netbsd:trap+0x96e
--- trap (number 4) ---
b7c21459:
  
But how can I tell where the trap comes frop? All threads are in system
calls, hence I assume the thing comes from kernel, but the I should
have a backtrace beyond trap(), shoudn't I?
(gdb) info threads
  Id   Target Id         Frame
* 1    LWP 1             0xb7bc0937 in _ksem_wait () from /lib/libc.so.12
  2    LWP 5             0xb7c21457 in ___lwp_park60 () from /lib/libc.so.12
  3    LWP 4             0xb7c21457 in ___lwp_park60 () from /lib/libc.so.12
  4    LWP 3             0xb7c21459 in ___lwp_park60 () from /lib/libc.so.12
  5    LWP 2             0xb7bbfdd7 in read () from /lib/libc.so.12
  6    LWP 6             0xb7bbfdd7 in read () from /lib/libc.so.12



-- 
Emmanuel Dreyfus
manu%netbsd.org@localhost