[PATCH] Fix signull test case

[Ulrich Weigand <weigand at i1 dot informatik dot uni-erlangen dot de>]

Hello,

the signull.exp test case fails when running under a 2.6 kernel,
because it uses longjmp to leave a SIGSEGV handler.  This results
in the signal remaining blocked for the rest of program execution,
and the second segmentation violation triggered by the test case
simply terminates the program.  The fix is to use siglongjmp.

Also, the test case uses 'signal' to install the signal handler;
according to POSIX it is undefined whether this routine installs
the handler with the 'one-shot' property or not.  (Apparently,
on BSD-like systems 'one-shot' is the default.)

Thus, I've also changed the test case to use sigaction instead,
to make sure the handler remains active across multiple invocations.
(This isn't currently an actual problem on Linux systems -- if you
prefer I can remove this part.)

Tested on s390-ibm-linux and s390x-ibm-linux, fixes one test suite
failure.

OK?


ChangeLog:

	* gdb.bas/signull.c: Use sigsetjmp/siglongjmp instead of 
	setjmp/longjmp.  Use sigaction instead of signal.

Index: gdb/testsuite/gdb.base/signull.c
===================================================================
RCS file: /cvs/src/src/gdb/testsuite/gdb.base/signull.c,v
retrieving revision 1.1
diff -c -p -r1.1 signull.c
*** gdb/testsuite/gdb.base/signull.c	13 May 2004 18:12:07 -0000	1.1
--- gdb/testsuite/gdb.base/signull.c	20 May 2004 13:10:52 -0000
***************
*** 19,24 ****
--- 19,25 ----
  
  #include <signal.h>
  #include <setjmp.h>
+ #include <stdlib.h>
  
  enum tests {
    code_entry_point, code_descriptor, data_pointer
*************** jmp_buf env;
*** 38,44 ****
  extern void
  keeper (int sig)
  {
!   longjmp (env, 0);
  }
  
  extern long
--- 39,45 ----
  extern void
  keeper (int sig)
  {
!   siglongjmp (env, 0);
  }
  
  extern long
*************** int
*** 59,68 ****
  main ()
  {
    static volatile int i;
!   signal (SIGSEGV, keeper);
    for (i = 0; i < 10; i++)
      {
!       setjmp (env);
        bowler ();
      }
  }
--- 60,74 ----
  main ()
  {
    static volatile int i;
! 
!   struct sigaction act;
!   memset (&act, 0, sizeof act);
!   act.sa_handler = keeper;
!   sigaction (SIGSEGV, &act, NULL);
! 
    for (i = 0; i < 10; i++)
      {
!       sigsetjmp (env, 1);
        bowler ();
      }
  }
-- 
  Dr. Ulrich Weigand
  weigand@informatik.uni-erlangen.de