#!/bin/sh

export LD_LIBRARY_PATH=
#export LD_SHOW_AUXV=1

cat>test.c<<'C'
#include <unistd.h>
#include <stdio.h>

int add(int x,int y);

int main(int argc,char** argv) {
    char buf[4096];
    int rd=readlink("/proc/self/exe",buf,sizeof(buf)-1); buf[rd]=0; // here is the problem
    printf("open link=%s\n",buf);
    return add(1,-1);
}

C

cat>add.c<<'C'
int add(int x,int y) { return x+y; }

C
#-m32
gcc -o libadd.so -shared add.c
gcc -o test test.c -L. -ladd -Xlinker '-rpath=$ORIGIN/libs'
mkdir -p libs
mv libadd.so libs

echo '--test in user fs--'
#ldd test
#strace ./test 2>&1 | grep open
./test

echo '--prepare fs archives--'
mkdir -p bin
sudo mount -t tmpfs -osize=1M none bin
cp test bin
mkdir -p bin/libs
cp libs/libadd.so bin/libs
rm -f bin.squashfs
mksquashfs bin bin.squashfs -comp xz 2>&1 > /dev/null
sudo umount bin

echo '--mount fs--'

sudo mount -t tmpfs -osize=1M none bin
mkdir bin/app bin/rom bin/diff
sudo mount -t squashfs -o ro,nouser bin.squashfs bin/rom
sudo mount -t overlayfs -o lowerdir=bin/rom,upperdir=bin/diff none bin/app
cd bin/app

echo '--test in mounted fs--'
./test
#strace ./test 2>&1 | grep open
echo '--work around--'
LD_LIBRARY_PATH=$PWD/libs ./test
#LD_ORIGIN_PATH=$PWD ./test 2>&1 | grep open
cd ../..
sudo umount bin/app
sudo umount bin/rom
sudo umount bin

--test in user fs--
open link=/home/kovserg/work/temp/readlink/test
--prepare fs archives--
--mount fs--
--test in mounted fs--
./test: error while loading shared libraries: libadd.so: cannot open shared object file: No such file or directory
--work around--
open link=/test

!/bin/sh

export LD_LIBRARY_PATH=
#export LD_SHOW_AUXV=1

cat>test.c<<'C'
#include <unistd.h>
#include <stdio.h>

int add(int x,int y);

int main(int argc,char** argv) {
    char buf[4096];
    int rd=readlink("/proc/self/exe",buf,sizeof(buf)-1); buf[rd]=0; // here is the problem
    printf("open link=%s\n",buf);
    return add(1,-1);
}

C

cat>add.c<<'C'
int add(int x,int y) { return x+y; }

C
#-m32
gcc -o libadd.so -shared add.c
gcc -o test test.c -L. -ladd -Xlinker '-rpath=$ORIGIN/libs'
mkdir -p libs
mv libadd.so libs

echo '--test in user fs--'
#ldd test
#strace ./test 2>&1 | grep open
./test

echo '--prepare fs archives--'
mkdir -p bin
sudo mount -t tmpfs -osize=1M none bin
cp test bin
mkdir -p bin/libs
cp libs/libadd.so bin/libs
rm -f bin.squashfs
mksquashfs bin bin.squashfs -comp xz 2>&1 > /dev/null
sudo umount bin

echo '--mount fs--'

sudo mount -t tmpfs -osize=1M none bin
mkdir bin/app bin/rom bin/diff bin/wrk
sudo mount -t squashfs -o ro,nouser bin.squashfs bin/rom
sudo mount -t overlay -o lowerdir=bin/rom,upperdir=bin/diff,workdir=bin/wrk none bin/app
cd bin/app

echo '--test in mounted fs--'
./test
#strace ./test 2>&1 | grep open
echo '--work around--'
LD_LIBRARY_PATH=$PWD/libs ./test
#LD_ORIGIN_PATH=$PWD ./test 2>&1 | grep open
cd ../..
sudo umount bin/app
sudo umount bin/rom
sudo umount bin

--test in user fs--
open link=/home/user/test/test
--prepare fs archives--
--mount fs--
--test in mounted fs--
open link=/home/user/test/bin/app/test
--work around--
open link=/home/user/test/bin/app/test

$ uname -a
Linux ubuntu 4.15.0-20-generic #21-Ubuntu SMP Tue Apr 24 06:16:15 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
$ lsb_release -a
No LSB modules are available.
Distributor ID:    Ubuntu
Description:    Ubuntu 18.04 LTS
Release:    18.04
Codename:    bionic