Hello, I bought the game today.
When I try to start the game I get a segmentation fault in the runner when running the start.sh.
I can see a small window frame popping up and then directly dying.

The last lines on the shell are (german system):
[...]
Anisotropic filtering supported, max aniso 16
This is where it would have set them fullscreen= 0, they are 640,480 displaywidth/h 1920,1200
Texture #1 16,16
Texture #2 16,16
./start.sh: Zeile 16: 6831 Speicherzugriffsfehler (Speicherabzug geschrieben) ./"runner"
(the last line means segmentation fault, core dumped)

When running the runner directly with gdb it says this (again the last lines):
This is where it would have set them fullscreen= 0, they are 640,480 displaywidth/h 1920,1200
Texture #1 16,16
Texture #2 16,16

Thread 8 "runner:sh1" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xe6dfeb40 (LWP 7030)]
0xed037d60 in llvm::PMTopLevelManager::schedulePass(llvm::Pass*) () from /usr/lib32/libLLVM-9.so

I tried it multiple times but the function where it dies seems to differ each run. I had also outputs like
0xed034c09 in llvm::PMDataManager::add(llvm::Pass*, bool) () from /usr/lib32/libLLVM-9.so
or 0xed034232 in llvm::PMDataManager::recordAvailableAnalysis(llvm::Pass*) () from /usr/lib32/libLLVM-9.so
in the debugger.

I also tried it with the play.it package but this also didn't help.

Any suggestions?
I am running arch linux with kernel linux 5.4.8.arch1-1 and the current mesa(19.3.1-1) and amdgpu(19.1.0) drivers.

SOLUTION
Ok, nevermind. I just found the answer in the AUR for the gog-undertale package (posted three days ago).
You just have to replace the ./runner row with
R600_DEBUG=check_vm ./runner

This should only affect amdgpu driver users.