Support for signals

[RobertBendun]

Requires #53.

Example

C code showing naive implementation of signals support

#define _GNU_SOURCE
#include <unistd.h>
#include <signal.h>
#include <sys/syscall.h>

void handle(int v)
{
	(void)v;

	syscall(SYS_write, 0, "whatsuppp?\n", 11);
}


#define SA_RESTORER 0x04000000

void restorer()
{
	syscall(SYS_rt_sigreturn);
}

int main()
{
	struct sigaction sa = {};
	sa.sa_handler = handle;
	sigemptyset(&sa.sa_mask);

#if 0
	sigaction(SIGINT, &sa, (void*)0);
#else
	sa.sa_flags |= SA_RESTORER;
	sa.sa_restorer = restorer;
	syscall(SYS_rt_sigaction, SIGINT, &sa, (void*)0, 8);
#endif

	usleep(10 * 1000000);
}