Firstly, why the fuck are you passing in a pointer to the shader handle? Just pass the int directly. Not that it will change anything here but come on now.

Also, don't use types like 'int' and 'unsigned int'. Use the unistd types instead.

Anyway, the debugging steps are pretty simple: start by inlining the function at the call site and see what happens, then see what happens with an empty shader, then play with the parameters, etc.

10 years ago I could have helped more directly but unfortunately I haven't touched opengl in quite a while

Do you know how to use gdb?

Good luck