Re: [musl] Shared library loading

[Rich Felker <dalias@libc.org>]

On Thu, Jun 04, 2020 at 10:37:40PM +0300, Alexander Scherbatiy wrote:
> On 25.05.2020 20:46, Rich Felker wrote:
> 
> >On Mon, May 25, 2020 at 08:26:51PM +0300, Alexander Scherbatiy wrote:
> >>   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.
> 
> OpenJDK can have several jvm variants (like server, client, minimal).
> Each of variants contains its own version of libjvm.so lib.
>   jdk/bin/java
>   jdk/lib/server/libjvm.so
>   jdk/lib/client/libjvm.so
>   jdk/lib/minimal/libjvm.so
> 
> When java is executed it first loads libjvm.so for the requested variant
> using dlopen() with RTLD_NOW | RTLD_GLOBAL flags [1] and then
> loads libraries from jdk/lib dir with dlopen() and RTLD_LAZY flag.
> 
> To make it works with musl JDK implements workaround where
> it puts libjvm.so into LD_LIBRARY_PATH [2] and re-executes itself.
> 
> Is there a better way to handle the case where an application
> with several lib variants can load common libraries
> without changing LD_LIBRARY_PATH?
> 
> [1] https://hg.openjdk.java.net/portola/portola/file/7ff60204a181/src/java.base/unix/native/libjli/java_md_solinux.c#l590
> [2] https://hg.openjdk.java.net/portola/portola/file/7ff60204a181/src/java.base/unix/native/libjli/java_md_solinux.c#l244

One way to do it would be to make dummy libraries libjvm_server.so,
libjvm_client.so, and libjvm_minimal.so that contain no code or data
but just a DT_NEEDED reference to libjvm.so and an appropriate
DT_RUNPATH to find it.

Rich