Date: Sun, 11 Oct 1998 15:20:55 +0800 From: Peter Wemm <peter@netplex.com.au> To: Bruce Evans <bde@zeta.org.au> Cc: bde@FreeBSD.ORG, cvs-all@FreeBSD.ORG, cvs-committers@FreeBSD.ORG Subject: Re: cvs commit: src/lib/libc/gen popen.c Message-ID: <199810110720.PAA19559@spinner.netplex.com.au> In-Reply-To: Your message of "Sun, 11 Oct 1998 16:24:52 %2B1000." <199810110624.QAA13368@godzilla.zeta.org.au>
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Bruce Evans wrote:
> >> More vfork breakage: vfork is used in about 50 programs in /usr/src.
> >> It is misused in all 7 programs that I looked at:
> >...
> >I suspect this has come about because of a change of implementation in
> >exec*(). I suspect they used to do something like:
> >
> >execl(arg1, arg2)
> >{
> > execve(arg1, &arg1, environ);
> >}
> >
> >... but since prototypes has been changed to use malloc etc and build an
> >array by sucking in args via va_arg() etc.
>
> ANSI should tell you that you can't do the above if a correct (varadic)
> prototype is in scope. NetBSD has ifdefs to do it anyway on arches where
> the varadic args are known to be on the stack.
Well, can we do it too? Or move it to the MD part of libc source
(eg: libc/i386/gen/execl.c) and the same on other systems that can do it?
If we "define" execl*() as not having side effects, it would help.
> >execl()
> >{
> > int count;
> > char **argv;
> >
> > count = (args by walking through the va_list with va_arg());
> > .. and rest of exec processing..
> > {
> > char *newargv[count + 1];
>
> This extension (variable length arrays) will be in C9x. I expect C9x
> will take longer to become normal than C89 (30 years instead of only
> 20? :-().
Heh. Somehow I suspect that language features are going to trickle
through much sooner. C++ supports this, doesn't it?
> We could just allocate ARG_MAX bytes on the stack. This has the same
> problems as alloca() and VLAs - stack memory isn't quite free. It
> may be better because it crashes more deterministically.
We could use this method as a fallback for systems that we can't pull
varadic args off the stack.
> Bruce
Cheers,
-Peter
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