Problem linking archive file (libz.a) - could not read symbols: file format not recognized

I am working in Ubuntu 16.04. I am new to Linux and cross-compiling. I am using cmake and libwebsockets (LWS) to make a webserver that will be cross-compiled to a ARM and loaded on a TS-7800 dev board.

I have installed LWS and have compiled .exe files in gcc (Ubuntu's native compiler, I guess) and also in the cross-compiler (arm-linux-gcc). The problem comes in when I want to add "things" to the executables, like libuv, or openssl.

Adding a test webserver (lwsws) to cmake (-DLWS_WITH_LWSWS=1) allows me to build the LWS files, but when I try to compile (make && sudo make install), i get:

/usr/lib/x86_64-linux-gnu/libz.a: could not read symbols: File format not recognized
collect2: ld returned 1 exit status

If I compile without the lwsws flag, I can build and compile. To me, that would indicate that the archive is okay. I don't understand why it is a problem with the lwsws flag.

All of this stuff worked fine with the native gcc compiler.

I have been working incrementally to maximize my success, but I can't seem to get out of the continuous road blocks that Linux throws my way.

Thanks for any tips you might have.

for me it looks like you want to cross link libs, so you tried to link x86_64 libs to an arm application.
Another cause can be: 32bit/64bit mismatch.

I told you I was new to this. I didn't realize I had to build libraries for the cross-compiler. Thanks for letting me know!

Originally Posted by severed_bit I was new to this

I'm really sorry, but it does not mean anything. I mean it is really hard to guess what do you really know and what is your real problem.
Giving more detailed description of your problem (what did you really execute, what's happened ... - make && sudo make install without context is meaningless too) could help us to give you better help.

But finally you could find the reason. That is good. Glad to head that.
Please mark the thread solved if you think your problem is now solved.