I really appreciate your detailed reply Brian. Having read your response I realised that creating a dll in cygwin is way over my head especially as I am limited on how much (more)time I can spend on this problem. I have since switched to using a linux platform and am having much more success.
Thanks a million :) Brian Dessent wrote: > > Brian Dessent wrote: > >> [...] your own initialization procedure that >> saves a copy of the bottom 4k, initializes Cygwin, and then restores the >> saved parts. > > Just to be clear, I don't mean that it should initialize Cygwin and then > restore those parts of the stack. > > To put it differently, when Cygwin initializes it expects to have free > reign of the bottom X bytes of the stack for its own use. You can > accomplish this two ways: > > The designed way - have code that runs very early in the sequence of > process initialization that simply allocates these bytes on the stack > like a standard C auto variable, and since the stack is nearly empty > they will be at the bottom. This is what the Cygwin startup code > (crt0.o) does when you run a Cygwin binary, and how it is designed to > work. > > The "fake it" way - Assume that you want to load the Cygwin DLL > dynamically at runtime, and the stack has already been robustly > allocated/populated by whatever application is already running. You > have no control over the bottom X bytes, so you're kind of screwed. The > best you can hope to do is make a copy of those X bytes, then initialize > Cygwin (which now "owns" that area and will overwrite whatever's there > with its own data) and hope that the control flow of the application is > such that you will be able to unload the Cygwin DLL and restore those > saved bytes before program flow reaches a point where the stack gets > unwound down to that earliest frame. > > If you don't take care of the deinitialization and restoration part then > everything will seem right but your application will probably crash and > die horribly when it terminates. > > Obviously the key here is that you need to run this initialization code > as early in the process init as possible. If I recall right the cygload > code tries to do this right at the beginning of main() and at that point > there is only a small amount of data at the bottom of the stack to > save/restore, which also means the best chances of that data not being > referenced/used before it is restored. > > [ X is sizeof(_cygtls) which has traditionally been less than 4K so 4K > is a nice round number but the current cygload actually uses 32k for a > safety margin, so the docs should be updated. ] > > Brian > > -- > Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple > Problem reports: http://cygwin.com/problems.html > Documentation: http://cygwin.com/docs.html > FAQ: http://cygwin.com/faq/ > > > -- View this message in context: http://www.nabble.com/Creating-a-dll-in-cygwin-for-use-with-jni-without--mno-cygwin-tf4238762.html#a12074866 Sent from the Cygwin Users mailing list archive at Nabble.com. -- Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple Problem reports: http://cygwin.com/problems.html Documentation: http://cygwin.com/docs.html FAQ: http://cygwin.com/faq/
