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SubjectRe: Changing argv[0] under Linux.
On Wed, Jan 15, 2003 at 12:41:30PM +0100, DervishD wrote:
> Hi JW :)
>
> > > > right after your envp. So, writing more info there would blow away
> > > > your stack.
> > > I can smell the next hack... memmove() the stack down to make room... :-)
> > No need. You can memcpy the environment. See setenv(3),
> > putenv(3) and related library routines.
>
> I'm afraid that the best solution, well, the one which involves
> less code and less problems (no need to relocate the environment or
> things like that) is to write to argv[0] a shorter string that the
> existing one, and overwrite with nulls the rest of arguments, just in
> case the stack layout is not what expected.
>
> Really, I'm thinking seriously about not rewritting argv[0] at
> all. The problem is that may confuse the user when issuing 'ps' or
> looking at /proc :((

What about

int main(int argc, char **argv) {
if (argc != 2 || (argv == 2 && !strcmp(argv[1], "--very-magic"))) {
char argv0[512];
memcpy(argv0, 'a', 511);
argv0[511] = 0;
char *const args[] = { argv0, "--very-magic", 0 };
execv(argv[0], args);
}
strcpy(argv[0], "my proggy");

/* your code here */
}

This should ensure that you have 511 bytes of argv[0] storage available,
if I read the previous posts correctly.

For the same effect without the --very-magic argument, you could simply
do an "if (argc != 2 || strlen(argv[0]) != 511)" instead.

Am I smoking crack, or could the above work?

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