kern/44432: cannot single-step over a call to sigprocmask()

[pooka%iki.fi@localhost]

>Number:         44432
>Category:       kern
>Synopsis:       cannot single-step over a call to sigprocmask()
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Jan 21 17:00:01 +0000 2011
>Originator:     Antti Kantee
>Release:        
>Organization:
>Environment:
NetBSD/i386 ~5.1
>Description:
gdb enters a loop eternal when single stepping over a call to
sigprocmask().
>How-To-Repeat:
#include <signal.h>
#include <stdio.h>

int
main()
{
        sigset_t set;

        sigfillset(&set);
        sigprocmask(SIG_SETMASK, &set, NULL);
        printf("hello, world!\n");

}

(gdb) break main
Breakpoint 1 at 0x8048761: file test.c, line 9.
(gdb) run
Starting program: /usr/home/pooka/a.out 

Breakpoint 1, main () at test.c:9
9               sigfillset(&set);
(gdb) next
10              sigprocmask(SIG_SETMASK, &set, NULL);
(gdb) 
*hang, a.out consumes 100% cpu*


Single stepping the same program on e.g. Linux works fine.
>Fix: