null pointers

What confuses me here is the date - Unixware had "nullptr", but did Linux have it ? And if it did, was it really what Jonathan mentions or was it just a replacement for comparing null pointers?

From: jls@sco.com (J. L. Schilling)
Newsgroups: comp.unix.sco.misc
Subject: Re: pointer sisters ...ah...question
Date: 22 Jun 2000 18:40:11 GMT
Message-ID: <8itmib$m5r$1@hobbes.sco.com> 
References: <8it7pl$tjk$1@rohrpostix.uta4you.at> 

Wolf Grossi (wg-news@magro-soft.com) wrote:
: Hi folks,
:     doing a port of a complex C-written software from svr4/unixware7.1 to
: linux/irix
: I'm running into the problem that UW7 does allow references to addresses
: pointing to 0X00, whereas Linux/IRIX gives sig 11 accessing an 0X00 address.

See nullptr(1).  By default the behavior is as you describe, but you can
change it to what you want.  You can also change it from within a running
program; see sysi86(2).

--
Jonathan Schilling              SCO, Inc.               jls@sco.com

From - Thu Jun 22 15:04:42 2000
From: Frank Langelage <langel@st-oneline.de>
Newsgroups: comp.unix.sco.misc
Subject: Re: pointer sisters ...ah...question
Date: Thu, 22 Jun 2000 20:26:33 +0200
Message-ID: <39525A59.EDD056A6@st-oneline.de> 
References: <8it7pl$tjk$1@rohrpostix.uta4you.at> 
X-Server-Date: 22 Jun 2000 18:32:07 GMT

On UW there is an Kernel Parameter called NULLPTR which controls this.
Default is 1: null-ptr reads are allowed
Set this to 0, if you want to get SIG 11 in your case.

Wolf Grossi schrieb:

> Hi folks,
>     doing a port of a complex C-written software from svr4/unixware7.1 to
> linux/irix
> I'm running into the problem that UW7 does allow references to addresses
> pointing to 0X00, whereas Linux/IRIX gives sig 11 accessing an 0X00 address.
>
> When accessing
> sub01(2....
> i expect sig 11, but UW7 just gives a null-string.
>
> I have attached a sample c-prog (tst01) to examine this case.
>
> UW7 output
> tst01 on UnixWare7, UNIX SVR4
> -----------------------------------
> 1: 08049658 NOT NULL... ''  <> px=0
> 2: 00000000 NULL...     0   <> px=0                          this should
> sig11 !!!!
> 3: FFFFFFFF NOT NULL...
> Pos=3, Sig 11 trapped...                                          good, -1
> is recognized...
>
> Linux result
> tst01 on Linux and IRIX
> -----------------------------------------
> 1: 0804858C NOT NULL... ''  <> px=2565888
> 2: 00000000 NULL...     0   <(null)>                            caught by
> printf
> Pos=20, Sig 11 trapped...                                         ok,
> reference to 0X00
>
> sample test "tst01.c"
> --------------------------
> #include <stdio.h>
> #include <signal.h>
> int pos=0;
> void sub01();
> void sig_trap();
> /* ************************************************************* */
> main()
> {
>   signal (SIGSEGV, sig_trap);
>   sub01(1, "''", (char *)"");
>   sub01(2, "0 ", (char *)0);
>   sub01(3, "-1", (char *)-1);
>   printf("terminating...\n");
>   return(0);
> }
> /* ************************************************************* */
> void sub01(int i1, char *s1, char *p1)
> { int px;
>
>   pos=i1;
>   printf("%d: ", pos);
>   if (p1 == (char *)0)
>      printf("%.8X NULL...     ", (long)p1);
>   else
>      printf("%.8X NOT NULL... ", (long)p1);
>   printf("%s  <%s>", s1, p1);                /* null is caught in printf
> (Linux, Irix) */
>   pos*=10;
>   memcpy((char *)&px, p1, sizeof(px)); /* dirty, I know, but must give sig11
> */
>   printf(" px=%d\n", px);
>   return;
> }
> /* ************************************************************** */
> void sig_trap(int sig)
> {
>   signal (SIGSEGV, sig_trap);
>   printf("\nPos=%d, Sig %d trapped...\n", pos, sig);
>   exit();
> }
> /* ************************************************************** */

From - Fri Jun 23 06:37:57 2000
From: jls@sco.com (J. L. Schilling)
Newsgroups: comp.unix.sco.programmer,comp.unix.sco.misc
Subject: Re: pointer sisters ...ah...question
Date: 23 Jun 2000 00:54:34 GMT
Message-ID: <8iucga$2ti$1@hobbes.sco.com> 
References: <8it7pl$tjk$1@rohrpostix.uta4you.at>
<sl4v52l3e7f24@corp.supernews.com> 

Robert Lipe (robertlipe@usa.net) wrote:

: by doing a 'nullptr disable'.  [...]

: There's the minor little detail that many core OS utilities become
: unstable when the system runs in this mode.  (Yes, I'm on a jihad to get
: the OS fixed, too....)

Yes, that's true, alas.  But it's important to note that the UnixWare 7 
system *libraries* are safe to run with the null pointer kludge disabled.  
That's why I pointed out that one can turn off the kludge from within one's
program as well as from the command line, by making a sysi86(SI86NULLPTR,...)
call.  The SCO JVM JIT compiler does this, for example, in order to 
efficiently implement Java's null reference checks by trapping null
pointer dereferences.

--
Jonathan Schilling              SCO, Inc.               jls@sco.com

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