export LD_PRELOAD for matlab MEX files

Question

I created a MEX executable and this one can be executed as a matlab function only if I export LD_PRELOAD all the needed libraries.

I wanted to automate this procedure cause it is using a bunch of in house made libraries and it's a tedious task to write export LD_PRELOAD every time in the terminal.

So I did a bash script:

#!/bin/bash
echo "PRELOAD MATLAB SCRIPT"

# Specify the folder containing the .so files
so_folder="/path/to/lib"

# Check if the folder exists
if [ ! -d "$so_folder" ]; then
  echo "The folder '$so_folder' does not exist."
  exit 1
fi

echo "Searching in .so folder: $so_folder ..."

# STD library problem from LINUX users only
export LD_PRELOAD=$LD_PRELOAD:/lib/x86_64-linux-gnu/libstdc++.so.6 matlab

# Set DACE library
export LD_PRELOAD=$LD_PRELOAD:/path/to/dace/lib/libdace.so matlab

# Loop through .so files in the folder
for so_file in "$so_folder"/*.so; do
  if [ -f "$so_file" ]; then
    # Set LD_PRELOAD and launch MATLAB for each .so file
    export LD_PRELOAD="$LD_PRELOAD:$so_file" matlab
    echo "Preloading library $so_file to MATLAB..."
  fi
done

Then, I call this script from the root of the project, where I also launch matlab afterwards:

$ bash scripts/preload_matlab_libs.sh

After it, I launch MATLAB and the .so files are not found as the error shows.

>> mex_test
Invalid MEX-file '/path/to/project/mex/mex_vsod.mexa64': libdace.so.2: cannot open
shared object file: No such file or directory

Error in mex_test (line 13)
b = mex_vsod(input1, input2)

No error is happening if I do the export LD_PRELOAD...

I'm a bit new in MEX compiled files. Therefore my questions:

• Why is the bash script not working? How do I fix it?
• Is there any other better approach to solve this issue?

Thanks!

Answer 1

The problem here is one of shell scripting, not MATLAB. Your script exports those variables into the shell running that script, but the way you're calling it, it cannot modify the calling script, so the values are lost by the time you start MATLAB. You can fix this by "sourcing" the shell script, which executes the lines of the script as-if you'd typed them at the prompt. Like this:

$ . scripts/preload_matlab_libs.sh
$ matlab

It would still be better to link your MEX files correctly so this isn't necessary. (By setting an RPATH or whatever)