Introduce signal handling #157
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Introduce the basic facilities to implement UNIX process signal handling in ucode. The VM structure is extended by a bitmap keeping track of received signal numbers, a sigaction structure which holds a generic signal handler to update the bitmap, a pipe where the generic signal handler will send received signal numbers to and an array of managed signal handler functions, indexed by signal number. Additionally, three new C API functions are added to control signal delivery in the VM instance: - `uc_vm_signal_dispatch()` This function invokes signal handler callbacks for each received signal number, clears the bitmap and empties the pipe. The VM itself will invoke this function after each executed bytecode instruction. In some cases however it is useful for C code driving the VM to force immediate signal delivery, e.g. from within long running C functions that do not return to ucode (to the next bytecode instruction) in a timely manner. - `uc_vm_signal_raise()` This function will deliver the given signal number, so that it is picked up by the next call to `uc_vm_signal_dispatch()`. It is used by the generic C signal handler function to forward received signals to the VM instance. - `uc_vm_signal_notifyfd()` This functions returns the read end of the internal signal pipe. It is mainly useful for integration into select or poll based event loops, in order to be notified when there's pending signals for delivery into the VM instance. Signed-off-by: Jo-Philipp Wich <jo@mein.io>
In order to prevent a premature release of the managed ucode signal handler callbacks, ensure to treat the containing array as GC root to mark the function values as reachable. Signed-off-by: Jo-Philipp Wich <jo@mein.io>
Enable signal dispatching by default for standalone ucode programs. Also adjust the `gc()` testcase output as the default number of allocations with enabled signal dispatching changes slightly. Signed-off-by: Jo-Philipp Wich <jo@mein.io>
The `signal()` standard library function provides functionality for registering signal handler callbacks, restoring default signal behaviour or ignoring specific signals. Signed-off-by: Jo-Philipp Wich <jo@mein.io>
When the VM instance loading the uloop module has signal dispatching enabled, implicitly register the signal pipe as file descriptor in the global uloop and dispatch received signals to the VM instance. This ensures that the respective managed ucode signal handlers are invoked immediately and not just after `uloop_run()` returns. Also end the uloop in case any invoked signal handler threw an exception, to match the expected behaviour with other kinds of callbacks. Signed-off-by: Jo-Philipp Wich <jo@mein.io>
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This PR introduces the infrastructure for handling UNIX signals inside ucode.