How to use dynamic linking to implement missing symbol in shared library with additional shared library

Question

I have a shared library in linux that was compiled using glibc and I want to run it in Alpine linux without recompiling it against Alpaine C libraries.

I found that there is solution to install gcompat - which is wrapper to Alpine C library to glibc and than with

patchelf --add-needed libgcompat.so.0 /var/lib/libdyn_MyLib.so

I can add the gcompat library into the my own library without compilation and it will tell the dynamic loader to look for symbols also in libgcompat.so

It worked partially and the ldd output of the shared library is:

ldd /var/lib/libdyn_MyLib.so
        /lib/ld-musl-x86_64.so.1 (0x7f79007cc000)
        libgcompat.so.0 => /lib/libgcompat.so.0 (0x7f78ff278000)
        libicudata.so.50 => /lib/libicudata.so.50 (0x7f78fdca4000)
        libicui18n.so.50 => /lib/libicui18n.so.50 (0x7f78fd8a6000)
        libicuuc.so.50 => /lib/libicuuc.so.50 (0x7f78fd52d000)
        libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x7f78fd2df000)
        libm.so.6 => /lib/ld-musl-x86_64.so.1 (0x7f79007cc000)
        libgomp.so.1 => /usr/lib/libgomp.so.1 (0x7f78fd298000)
        libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0x7f78fd27a000)
        libpthread.so.0 => /lib/ld-musl-x86_64.so.1 (0x7f79007cc000)
        libc.so.6 => /lib/ld-musl-x86_64.so.1 (0x7f79007cc000)
        ld-linux-x86-64.so.2 => /lib/ld-linux-x86-64.so.2 (0x7f78fd274000)
        libucontext.so.1 => /lib/libucontext.so.1 (0x7f78fd26f000)
        libobstack.so.1 => /usr/lib/libobstack.so.1 (0x7f78fd26a000)
        libdl.so.2 => /lib/ld-musl-x86_64.so.1 (0x7f79007cc000)
Error relocating libdyn_MyLib.so: feenableexcept: symbol not found

I can see that libgcompat.so is listed and there are no "not found" libraries.

All the "symbol not found" disappeared except for "feenableexecpt".

After referring to documentation, feenableexecpt is extension of glibc and not supported in gcompat package and I can understand why it's hard to support it.

I want to ignore this function call so I tried to implement "feenableexecpt" that does nothing and add this library to libdyn_MyLib.so (like implementing my own feenableexecpt that does nothing as they implement glibc library using different library).

Here is my code:

glibc_extension.h:

#ifndef __ALPINE_GLIBC__
#define __ALPINE_GLIBC__
extern int feenableexcept(int __excepts) throw ();
#endif

lib_ext.cpp:
#include "glibc_extension.h"

int feenableexcept(int e) throw () {
    return 0;
}

complied it as share library:

gcc -Wall -Werror -shared -o libalpine.so lib_ext.cpp

I can see feenableexecpt in the symbols table using nm.

I had also used patchelf to add this library to my shared library, here is the output of the shared library again:

ldd /var/lib/libdyn_MyLib.so
        /lib/ld-musl-x86_64.so.1 (0x7f79007cc000)
        libalpine.so => /lib/libalpine.so (0x7f78ff28b000)
        libgcompat.so.0 => /lib/libgcompat.so.0 (0x7f78ff278000)
        libicudata.so.50 => /lib/libicudata.so.50 (0x7f78fdca4000)
        libicui18n.so.50 => /lib/libicui18n.so.50 (0x7f78fd8a6000)
        libicuuc.so.50 => /lib/libicuuc.so.50 (0x7f78fd52d000)
        libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x7f78fd2df000)
        libm.so.6 => /lib/ld-musl-x86_64.so.1 (0x7f79007cc000)
        libgomp.so.1 => /usr/lib/libgomp.so.1 (0x7f78fd298000)
        libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0x7f78fd27a000)
        libpthread.so.0 => /lib/ld-musl-x86_64.so.1 (0x7f79007cc000)
        libc.so.6 => /lib/ld-musl-x86_64.so.1 (0x7f79007cc000)
        ld-linux-x86-64.so.2 => /lib/ld-linux-x86-64.so.2 (0x7f78fd274000)
        libucontext.so.1 => /lib/libucontext.so.1 (0x7f78fd26f000)
        libobstack.so.1 => /usr/lib/libobstack.so.1 (0x7f78fd26a000)
        libdl.so.2 => /lib/ld-musl-x86_64.so.1 (0x7f79007cc000)
Error relocating libdyn_MyLib.so: feenableexcept: symbol not found

I can see libalpaine.so in the ldd output but still "feenableexecpt" is missing.

What have I done wrong?

Thanks

I was expecting the feenableexecpt symbol to be found by the dynamic program executer.