Date: Mon, 21 Jul 2003 14:59:28 -0400 From: Leo Bicknell <bicknell@ufp.org> To: Tim Kientzle <kientzle@acm.org>, Chad David <davidc@issci.ca>, hackers@freebsd.org Subject: Re: Correct way to call execve? Message-ID: <20030721185928.GA61664@ussenterprise.ufp.org> In-Reply-To: <20030721185217.GA60600@ussenterprise.ufp.org> References: <3F1B0610.90803@acm.org> <20030720225041.GA26277@ussenterprise.ufp.org> <3F1C0C91.6050203@acm.org> <20030721165735.GA56766@ussenterprise.ufp.org> <20030721171538.GA21656@colnta.acns.ab.ca> <20030721172321.GA57666@ussenterprise.ufp.org> <20030721174206.GA21892@colnta.acns.ab.ca> <3F1C2FEB.4070801@acm.org> <20030721185217.GA60600@ussenterprise.ufp.org>
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You know, my own thinking made me figure this one out:
% cat exec.c
#include <unistd.h>
#include <paths.h>
#include <string.h>
int main(int argc, char *const argv[], char *const envp[]) {
char *const execargv[] =3D { _PATH_BSHELL, NULL };
execve(_PATH_BSHELL,execargv,NULL);
return 0;
}
% cc -fwritable-strings -Wcast-qual -Wwrite-strings exec.c
%
There you go. By default strings are read-only, and indeed smart
compilers use that to compress them and do other nifty tricks. However,
in this case you really want a string to be "char *", eg writable.
So, tell the compiler to do that with "-fwritable-strings", poof,
strings are now "char *", the cast away the cost problem goes away,
"-Wcast-qual" works fine.
It always seemed to me a lot of things included -fwritable-strings for
no good reason, maybe this is part of the reason. :)
--=20
Leo Bicknell - bicknell@ufp.org - CCIE 3440
PGP keys at http://www.ufp.org/~bicknell/
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