Date: Mon, 25 May 2020 13:46:33 -0400 From: Rich Felker <dalias@...c.org> To: Alexander Scherbatiy <alexander.scherbatiy@...l-sw.com> Cc: musl@...ts.openwall.com, Markus Wichmann <nullplan@....net> Subject: Re: Shared library loading On Mon, May 25, 2020 at 08:26:51PM +0300, Alexander Scherbatiy wrote: > On 22.05.2020 21:25, Rich Felker wrote: > > >The concept here is that non-pathname library names should be loaded > >from the library path and not replaced by something (typically a > >"module" or "plug-in") in a different, explicitly-loaded location that > >happens to have a colliding base filename. > > > >For example suppose your application loads modules from $libdir/myapp/ > >and has a module named "libfoo.so". Unbeknownst to you, there's also a > >"libfoo.so" in the system paths, and some library you potentially load > >indirectly (maybe the GPU driver for some video hardware you've never > >heard of) depends on "libfoo.so". > > > >If dlopen("$libdir/myapp/libfoo.so") had put "libfoo.so" in the > >namespace such that it would satisfy future load requests for the name > >"libfoo.so", the subsequent load would break due to getting the wrong > >(unrelated) library. > Is it correct that RTLD_GLOBAL flag is in some kind of obsolete in > musl because calling > dlopen("$libdir/myapp/libfoo.so", RTLD_NOW | RTLD_GLOBAL); > dlopen("$libdir2/myapp2/libbar.so", RTLD_LAZY); > > does not allow libbar.so to find library $libdir/myapp/libfoo.so > which it is depend on? This is not what RTLD_GLOBAL means. RTLD_GLOBAL is a matter of whether the library's symbols appear in the global symbol namespace to resolve relocations in future-loaded libraries and dlsym with RTLD_DEFAULT. It has nothing to do with whether the library is visible for satisfying DT_NEEDED. The library is *always* visible for this purpose. > What is the suggested way in musl to load $libdir/myapp/libfoo.so > from a custom directory so libbar.so can find it? Probably putting the dir in your application's rpath (or in the rpath of libbar). dlopen is not a tool for (effectively) adding additional directories to the library search path. Rich
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