port-amd64/43835: ksh(1) regression under compat_netbsd32

[njoly%pasteur.fr@localhost]

>Number:         43835
>Category:       port-amd64
>Synopsis:       ksh(1) regression under compat_netbsd32
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-amd64-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Sep 03 13:50:01 +0000 2010
>Originator:     Nicolas Joly
>Release:        NetBSD 5.99.39
>Organization:
Intitut Pasteur
>Environment:
System: NetBSD lanfeust.sis.pasteur.fr 5.99.39 NetBSD 5.99.39 (LANFEUST) #14: 
Thu Sep 2 11:23:23 CEST 2010 
njoly%lanfeust.sis.pasteur.fr@localhost:/local/src/NetBSD/obj.amd64/sys/arch/amd64/compile/LANFEUST
 amd64
Architecture: x86_64
Machine: amd64
>Description:
i386 ksh(1) does not work anymore under compat_netbsd32 with the following
$HOME/.kshrc file ... No problem with native version.

njoly@lanfeust [~]> cat .kshrc
ARCH=$(uname -m)
echo $ARCH

njoly@lanfeust [~]> file /bin/ksh 
/bin/ksh: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically 
linked (uses shared libs), for NetBSD 5.99.39, not stripped
njoly@lanfeust [~]> /bin/ksh   
amd64
$ 

njoly@lanfeust [~]> file /misc/chroot/netbsd32/bin/ksh 
/misc/chroot/netbsd32/bin/ksh: ELF 32-bit LSB executable, Intel 80386, version 
1 (SYSV), dynamically linked (uses shared libs), for NetBSD 5.99.39, not 
stripped
njoly@lanfeust [~]> /misc/chroot/netbsd32/bin/ksh 
njoly@lanfeust [~]> echo $?
255

Tracing show that netbsd32_setcontext() syscall is failling:
[...]
 25351      1 ksh      RET   netbsd32___getrusage50 0
 25351      1 ksh      CALL  netbsd32___gettimeofday50(0xffffd2cc,0)
 25351      1 ksh      RET   netbsd32___gettimeofday50 0
 25351      1 ksh      CALL  netbsd32___wait450(0xffffffff,0xffffd348,3,0)
 25351      1 ksh      RET   netbsd32___wait450 -1 errno 10 No child processes
 25351      1 ksh      CALL  netbsd32_setcontext(0xffffd41c,0xffffd41c,0x14)
 25351      1 ksh      RET   netbsd32_setcontext -1 errno 22 Invalid argument
 25351      1 ksh      CALL  netbsd32_exit(0xffffffff)

>How-To-Repeat:
Run i386 ksh(1) under compat_netbsd32, with appropriate .kshrc file
>Fix: