I want to debug App2.exe, which is started by App1.exe. If App2.exe were a dll I could specify a host application, but this doesn't seem to work with an .exe.
I now use 'attach to process', but this is useless if App2.exe crashes before I do that.
Is there a way to do this with having to attach to the process manually?
No, but there might be a way to get it to attach properly. Find something that you know will happen in App2 soon before the crash point, and have it pop up a modal dialog box at that point. Then it won't continue until you dismiss it, giving you time to attach the debugger.
I guess you could launch app2.exe yourself and pass any necessary command line parameters to it.
If both apps are yours and you have the code than I propose the following:
I have a project where a server spawns multiple exe worker processes that host each its own dll module. I have a debug mode in which I can specify which dll will be loaded and I can have both processes running and communicationt in between from IDEs. It is the best way I have found so far.
Set the "debug spawned processes" debugging option. It is off by default. When App1 starts the new process, the debugger will pause. If the debugger isn't already attached to the new process automatically, attach to it, and then resume running it.
If you're using windows, there is a built in support for it. basically, you can tell the windows loader to launch some other process whenever a specific process is launched. for example, you can tell windows to always launch winword.exe whenever you click on notepad.exe
you can use this ability in order to automatically launch a debugger whenever you start your process (this is why this feature was originally introduced, however you are not restricted to launch only debuggers :))
You can read exactly how to do it here. You can also download the debugging tools for windows package and use GFlags to do it for you.