One other thing I am interested in, what is the output of LWP's
  configure. I wonder which type of thread switching it picked. I think
  NetBSD deprecated makecontext and friends, so it might be using tricks
  with signal handlers (sigaltstack) to kickstart new threads, or it could
  be falling back on the old assembly code which might not realize that
  this is a 32-bit kernel/userspace. So it could be that the first thread
  switch is trying to perform a 64-bit read which triggers the bus error.

A very interesting possibility.

It would be cool to have a lwp-config program that outputs information
about what it chose.  I think ucontext is being used.

But with the NetBSD/sparc userland, the #defines in force should be as
for sparc (not sparc64).  (uname -m used?)


I built lwp on NetBSD/sparc64 (native, so 64-bit kernel and userland).

gdt-sparc64 86 ~/SOFTWARE/CODA/lwp/src > size *.o
   text    data     bss     dec     hex filename
    764      16       0     780     30c cswitch.o
    180       0       4     184      b8 liblwp_la-fasttime.o
   4272       0    2936    7208    1c28 liblwp_la-iomgr.o
   1292       0       0    1292     50c liblwp_la-lock.o
   9616      32    1504   11152    2b90 liblwp_la-lwp.o
      8       0       0       8       8 liblwp_la-lwp_stacktrace.o
      0       0       0       0       0 liblwp_la-lwp_ucontext.o
    948       0       4     952     3b8 liblwp_la-timer.o
      0       0       0       0       0 process.o
   1588     328       0    1916     77c rw.o
   1792       0       0    1792     700 tdb.o
    888      16       0     904     388 testlwp.o

testlwp and rw both work, and tdb crashes:

gdt 89 ~/SOFTWARE/CODA/lwp/src > libtool gdb tdb
*** Warning: inferring the mode of operation is deprecated.
*** Future versions of Libtool will require --mode=MODE be specified.
GNU gdb 5.3nb1
Copyright 2002 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "sparc64--netbsdelf"...
(gdb) run
Starting program: /usr/home/gdt/SOFTWARE/CODA/lwp/src/.libs/tdb 
Main thread going to create procA
Main thread going to create procB
Main thread going to create procC 
Main thread returned from creating procC  
procA starting ...

Program received signal SIGSEGV, Segmentation fault.
0x0000000040205cd8 in _rtld_symlook_list () from /usr/libexec/ld.elf_so




On NetBSD-current on i386, I get

/* config.h.  Generated by configure.  */
/* config.h.in.  Generated from configure.in by autoheader.  */

/* Define to 1 if you have the <dlfcn.h> header file. */
#define HAVE_DLFCN_H 1

/* Define to 1 if you have the `getpagesize' function. */
#define HAVE_GETPAGESIZE 1

/* Define to 1 if you have the <inttypes.h> header file. */
#define HAVE_INTTYPES_H 1

/* Define to 1 if you have the <memory.h> header file. */
#define HAVE_MEMORY_H 1

/* Define to 1 if you have a working `mmap' system call. */
#define HAVE_MMAP 1

/* Define to 1 if the system has the type `register_t'. */
#define HAVE_REGISTER_T 1

/* Define to 1 if you have the `sigaltstack' function. */
#define HAVE_SIGALTSTACK 1

/* Define to 1 if the system has the type `stack_t'. */
#define HAVE_STACK_T 1

/* Define to 1 if you have the <stdint.h> header file. */
#define HAVE_STDINT_H 1

/* Define to 1 if you have the <stdlib.h> header file. */
#define HAVE_STDLIB_H 1

/* Define to 1 if you have the <strings.h> header file. */
#define HAVE_STRINGS_H 1

/* Define to 1 if you have the <string.h> header file. */
#define HAVE_STRING_H 1

/* Define to 1 if you have the <sys/stat.h> header file. */
#define HAVE_SYS_STAT_H 1

/* Define to 1 if you have the <sys/types.h> header file. */
#define HAVE_SYS_TYPES_H 1

/* Define to 1 if you have the <ucontext.h> header file. */
#define HAVE_UCONTEXT_H 1

/* Define to 1 if you have the <unistd.h> header file. */
#define HAVE_UNISTD_H 1

/* Name of package */
#define PACKAGE "lwp"

/* Define to the address where bug reports for this package should be sent. */
#define PACKAGE_BUGREPORT ""

/* Define to the full name of this package. */
#define PACKAGE_NAME ""

/* Define to the full name and version of this package. */
#define PACKAGE_STRING ""

/* Define to the one symbol short name of this package. */
#define PACKAGE_TARNAME ""

/* Define to the version of this package. */
#define PACKAGE_VERSION ""

/* Define to 1 if you have the ANSI C header files. */
#define STDC_HEADERS 1

/* Version number of package */
#define VERSION "2.1"



-- 
        Greg Troxel <gdt_at_ir.bbn.com>