Date: Mon, 29 Oct 2001 04:05:37 -0800 (PST) From: Lamont Granquist <lamont@scriptkiddie.org> To: <freebsd-hackers@freebsd.org> Subject: Re: MT-Safe wrapper around memcpy()? Message-ID: <20011029040255.D27876-100000@coredump.scriptkiddie.org> In-Reply-To: <20011029005821.X15052@elvis.mu.org>
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On Mon, 29 Oct 2001, Alfred Perlstein wrote:
> * Alfred Perlstein <bright@mu.org> [011029 00:53] wrote:
> > * Lamont Granquist <lamont@scriptkiddie.org> [011029 00:43] wrote:
> > >
> > > I'm trying to figure out the best way to write a wrapper around memcpy()
> > > which can call fprintf() without winding up getting into a recursive
> > > loop. The problem is that fprintf() will call memcpy() and around and
> > > around we go.
> > >
> > > I can use a global variable to prevent this, but that usage isn't thread
> > > safe. I can make it thread safe by using pthread keys, but then i have to
> > > link in libc_r, and for non-pthreaded programs i don't want to do that.
> > >
> > > Anyone have any suggestions? Right now I'm almost thinking that I just
> > > need to directly patch libc and libc_r. It might be an ugly patch though,
> > > and I'd rather not have this patch mandate recompiling all of libc.
> >
> > Where do you see mem* calling printf?
>
> Uh, nevermind. :)
>
> Ok, what you want to do is use a nested flag in memcpy so you
> don't recurse, there's some code in libc that's conditionally
> compiled when compiling libc_r, _THREAD_SAFE or something is
> defined, once you find that then just simply use the global
> for non threaded programs and keys for threaded ones.
you mean like localtime.c:
#ifdef _THREAD_SAFE
pthread_mutex_lock(&lcl_mutex);
#endif
and such?
problem is that i could do that if i was dropping it into libc itself, but
as a single .so that i want to LD_PRELOAD, i need a run-time conditional
rather than a precompiler conditional. i think i may be asking for a
lot...
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