Ewgenij Gawrilow wrote:
Hello, is somebody out there who has consciously used the asynchronous unwind tables? The GCC documentation does not reveal much more about this feature than the mere statement of its existence. What I eventually need is the possibility to catch certain signals and unwind a part of the stack down to a certain frame in a mixed C / C++ program. A naive approach of throwing an exception from the signal handler does not work, neither does a siglongjump from the handler unwind the stack frames between it and the frame where sigsetjump was executed (although some C++ ABI drafts suggested this behaviour). The main problem is probably the kernel-generated frame of the signal handler, lying between the frame where unwinding starts and the catching frame. If I set up the signal handler to use the alternative stack, this frame won't be an obstacle any more; but I didn't find any clue how to tell the unwinding machinery (_Unwind_RaiseException and the relatives) as it is implemented in libgcc, that it has to scan over a different stack. I'd deeply appreciate any helpful advice and tips. The solution needn't be universally portable; I'll be overly glad to get it running under Linux on i386 and x86_64, and in the further future, if possible, under MacOS.
libgcj (GCC's java runtime library) does exactly what you describe for synchronous signals (SIGSEGV, SIGFPE). Throwing exceptions through such signal frames does work for both i386 and x86_64 (as well as many other architectures) on linux. Unwinding from arbitrary asynchronous signals (SIGUSR1 etc.) is not supported.
The code that does it can be found in libjava/prims.cc David Daney
