Date: Fri, 22 May 2020 21:07:20 +0300 From: Alexander Scherbatiy <alexander.scherbatiy@...l-sw.com> To: musl@...ts.openwall.com, Markus Wichmann <nullplan@....net> Subject: Re: Shared library loading On 21.05.2020 18:21, Markus Wichmann wrote: > On Thu, May 21, 2020 at 02:27:24PM +0300, Alexander Scherbatiy wrote: >> Hello, >> >> I use Alpine Linux 3.11.6 with musl libc (x86_64) version 1.1.24. >> >> I have two shared libraries "a" and "b" each of which is placed in its own >> directory and lib "b" depends on "a". >> First, I use dlopen to load lib "a" with "RTLD_NOW | RTLD_GLOBAL" flags. >> Second, I load lib "b" with flag "RTLD_LAZY". >> >> The "b" library loading works on my Ubuntu 19.10 and fails on Alpine 3.11.6 >> with message: >> dlopen failed: Error loading shared library liba.so: No such file or >> directory (needed by /root/load-lib-sample/bin/b/libb.so) >> Should it work on Alpine with musl libc as well? > [...] > > I shall leave the "Should it work" to others who know more about this > than me. But I will tackle the "Why doesn't it work". It appears however > the behavior is intentional (whether the consequences are as well > remains to be seen). Namely in line 1140f. of dynlink.c (revision > 72658c65): > > > |/* Add a shortname only if name arg was not an explicit pathname. */ > |if (pathname != name) p->shortname = strrchr(p->name, '/')+1; It would be interesting to know which task this check is supposed to solve. Thanks, Alexander. > > This means, in your case, the DSO handle for liba does not get a short > name, so when libb is loaded, it is not detected that liba has already > been loaded (only the shortname is used for that purpose). And since > your files are in different directories, liba is also not found to be > loaded again. To work around this, you can set LD_LIBRARY_PATH to the > directory containing liba. In that case, when loading libb, the > dependency will be found with the environment search, and since liba was > already loaded, the loop in lines 1085ff. will find the handle and even > assign a shortname. The shortname is only used for checking of > duplicates. > > Ciao, > Markus
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