Date: Tue, 2 Jul 2019 12:56:39 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Baptiste Daroussin <bapt@FreeBSD.org> Cc: Yuri <yuri@rawbw.com>, Freebsd hackers list <freebsd-hackers@freebsd.org>, Shawn Webb <shawn.webb@hardenedbsd.org> Subject: Re: Question: Is there a way to get the list of all dynamic libraries needed by a given elf through API? Message-ID: <20190702095639.GA47193@kib.kiev.ua> In-Reply-To: <20190702071200.qy6hr5yhaczhj6wx@ivaldir.net> References: <dfac779f-fa4f-a292-1a76-a9e7db5e024a@rawbw.com> <20190702031523.lhlrqnlo7pxccl42@mutt-hbsd> <c04b30b9-8f1f-15dc-f93d-e3d8cd1f5fa0@rawbw.com> <20190702071200.qy6hr5yhaczhj6wx@ivaldir.net>
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On Tue, Jul 02, 2019 at 09:12:00AM +0200, Baptiste Daroussin wrote: > On Mon, Jul 01, 2019 at 10:27:25PM -0700, Yuri wrote: > > On 2019-07-01 20:15, Shawn Webb wrote: > > > $ ldd -f '%p\n' /bin/ls > > > > > > Hi Shawn, > > > > > > ldd doesn't do what I need. It sets one specific environment variable, then > > forks and calls execl(3). > > > > And I am looking for the API function like: char* > > find_shared_library_mapping(const char *so_lib, char *buf_out, size_t > > buf_out_sz); // or something like this. > > > Use libelf, and read the dynamic section which will give you everything you > want: > > readelf -d which uses libelf, will give you this with all the NEEDED tag. > The same way you can get the runpath and rpath > > Tag Type Name/Value > 0x0000000000000001 NEEDED Shared library: [libutil.so.9] > 0x0000000000000001 NEEDED Shared library: [libncursesw.so.8] > 0x0000000000000001 NEEDED Shared library: [libc.so.7] > > The good thing about it is that you will you will only get the direct > dependency. > > This is through this lib that pkg extract the list of required libraries Rtld rules for search paths preferences are very convoluted. Look at the ld-elf.so.1 man page about it, rpath vs. runpath, and the effects of the environment variables, and the caller settings, and tags expansion which rewrites DT_NEEDED and rpath. The question 'which file is used to satisfy this DT_NEEDED tag' can be only correctly answered in context of the image activation or dlopen(3) call, due to all the factors affecting the selection. Even the location of the code which called dlopen(3) is important. The consequence is that such API cannot exist in reliable form.
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