Date: Thu, 13 Nov 2008 09:00:21 +0100 From: Markus Hoenicka <markus.hoenicka@mhoenicka.de> To: Jeremy Chadwick <koitsu@FreeBSD.org> Cc: freebsd-questions@FreeBSD.org Subject: Re: dlsym can't use handle returned by dlopen? Message-ID: <20081113090021.less3h5iwwsgwsg4@webmail.df.eu> In-Reply-To: <20081113042912.GA10018@icarus.home.lan> References: <18715.28127.306511.577084@yeti.mininet> <20081113042912.GA10018@icarus.home.lan>
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Quoting Jeremy Chadwick <koitsu@FreeBSD.org>: > I know that the .so's you're loading with dlopen() need to be built a > specific way/with certain arguments, otherwise they won't work (I > believe what I saw was dlsym() returning NULL). My symbol names were > getting stomped on, and there was a compiler flag that addressed that. > Is that a BSD-specific problem? As mentioned previously, I don't run =20 into trouble on other platforms. Is there any documentation available =20 which tells me how to build a dlopen()'able object in a portable way? >> function_pointer =3D dlsym(RTLD_DEFAULT, "function_name"); >> >> Why is that? Or rather: what am I doing wrong? > > This code right here is *completely* wrong. RTLD_DEFAULT is a mode bit > for dlopen(). I'm willing to bet a strict set of warnings would Citing the FreeBSD dlsym(3) man page: "If dlsym is called with the special handle RTLD_DEFAULT, the =20 search for the symbol follows the algorithm used for resolving =20 undefined symbols when objects are loaded." You probably had RTLD_LAZY and RTLD_NOW in mind which are dlopen() =20 flags. BTW RTLD_NEXT works just as well instead of RTLD_DEFAULT. regards, Markus --=20 Markus Hoenicka markus.hoenicka@cats.de (Spam-protected email: replace the quadrupeds with "mhoenicka") http://www.mhoenicka.de
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