Henry S. Thompson writes: This looks like a stack overflow, something that is easily triggered by the regular expression search code and its use of alloca() to grab large blocks of memory off the stack. If you can increase your stacksize under Cygwin, try doubling it and see if it makes the problem go away. XEmacs could be made to do this for the user, or XEmacs could be compiled with REGEX_MALLOC by default in environments that have an insuffieciently large default stack size.

Henry S. Thompson writes: When you see the error "Stack overflow in regexp matcher" this refers to a number of errors that might occur in the regex code, one of which is the overflow of the matcher's failure stack. It doesn't refer to the operating system controlled stack, which is what I think is being exhaused by alloca() calls. Your Solaris build most likely was not using alloca() for the failure stack. If your XEmacs was compiled with the relocating allocator enabled, then that allocator rather than alloca() is used for the failure stack. The relocating allocator allocates off the heap rather than the stack so you won't see a stack overflow from its use. The relocating allocator is enabled by default for most operating systems. But under Cygwin the relocating allocator is disabled by default, so when you moved from Solaris to Cygwin, you likely started using alloca() and so your previously benign internal stack overflow became a hard OS level stack overflow which crashed the editor. There's no way that I know of to determine whether an alloca() call is going to succeed or generate a SIGSEGV. So in order to handle OS level stack overflows XEmacs will have to wrap alloca() calls somehow, probably with a signal handler that longjmp()'s back to some known safe place and then signals an error. Arguably it is, if the problem is rare. This is not a buffer overrun sort of problem with the attendant security vulnerability. What happens is XEmacs asks for more stack space than the process is allowed to use, and the kernel's response is to send a SIGSEGV. I think XEmacs should handle it if it can, since crashes are obviously to be avoided.