Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!clyde!rutgers!sri-spam!mordor!lll-tis!ptsfa!ihnp4!cuae2!ltuxa!ttrdc!levy
From: levy@ttrdc.UUCP
Newsgroups: comp.unix.questions
Subject: Re: Destroying arguments
Message-ID: <1717@ttrdc.UUCP>
Date: Tue, 19-May-87 20:00:16 EDT
Article-I.D.: ttrdc.1717
Posted: Tue May 19 20:00:16 1987
Date-Received: Fri, 22-May-87 01:02:45 EDT
References: <292@osupyr.UUCP> <239@polyof.UUCP> <485@bene.UUCP> <6723@mimsy.UUCP> <19131@sun.uucp>
Distribution: comp.unix.questions
Organization: AT&T, Skokie, IL
Lines: 52

In article <19131@sun.uucp>, guy%gorodish@Sun.COM (Guy Harris) writes:
> The 3B2 version of "ps" does it
> differently; the kernel stashes a string away in the U area that
> contains the original arguments used to invoke the program.  (I have
> no idea whether this was done because somebody thought this was the
> right way to do things, or because they couldn't figure out how to
> snarf the arguments up on a machine whose stack grows upward in
> memory....)  On this machine, you *can't* smash your argument list.
> Period.
> The answer is "forget it".  In general, it can't be done.

This may well be true on some machines and implementations, but don't
unjustly blacken the 3B2, please.  I tried this code on a 3B2/400
running System V Release 2.0.4 swapping:

main(argc,argv)
int argc;
char *argv[];
{
	int i;
	char *c;
	void perror();

	for (i=0; i<argc; i++)
		for (c=argv[i]; *c; c++)
			*c = 'X';	/* stomp all over argv */

	if (fork() == 0) {
		(void) execl("/bin/ps", "ps", "-f", (char *) 0);
		perror("Can't execute /bin/ps");
	}
	else
		(void) wait((int *)0);	/* hang around till ps finishes */

	return 0;
}

The results (call the program stompargv):

$ stompargv arg_one arg_two arg_three
     UID   PID  PPID  C    STIME TTY      TIME COMMAND
    levy  1603     1  0 16:30:04 tty11    0:03 -sh
    levy  1605  1603  7 18:40:18 tty11    0:00 XXXXXXXXX XXXXXXX XXXXXXX XXXXXXXXX
    levy  1606  1605 44 18:40:18 tty11    0:00 ps -f

(Could someone please try this on SVR3 3B2 and tell me if it works the
same way?)
-- 
|------------dan levy------------|  Path: ..!{akgua,homxb,ihnp4,ltuxa,mvuxa,
|         an engihacker @        |		vax135}!ttrdc!ttrda!levy
|    at&t data systems division  |  Disclaimer:  try datclaimer.
|--------skokie, illinois--------|