Kernel/LibC: Add bareboness signals

You can now call raise() to raise a signal. Signal handlers are
not yet supported, but the handling works :)

kernel/kernel/Process.cpp

@@ -14,6 +14,9 @@
 #include <stdio.h>
 #include <sys/sysmacros.h>
 
+extern "C" void signal_trampoline();
+extern "C" void test_signal();
+
 namespace Kernel
 {
 
@@ -788,6 +791,27 @@ namespace Kernel
 		return 0;
 	}
 
+	BAN::ErrorOr<long> Process::sys_raise(int signal, uintptr_t& return_rsp, uintptr_t& return_rip)
+	{
+		if (signal < _SIGMIN || signal > _SIGMAX)
+			return BAN::Error::from_errno(EINVAL);
+
+		ASSERT(&Process::current() == this);
+
+		LockGuard lock_guard(m_lock);
+		asm volatile("cli");
+
+		uintptr_t* return_rsp_ptr = (uintptr_t*)return_rsp;
+		*--return_rsp_ptr = return_rip;
+		*--return_rsp_ptr = signal;
+		*--return_rsp_ptr = (uintptr_t)test_signal;
+
+		return_rsp = (uintptr_t)return_rsp_ptr;
+		return_rip = (uintptr_t)signal_trampoline;
+
+		return 0;
+	}
+
 	BAN::ErrorOr<long> Process::sys_setuid(uid_t uid)
 	{
 		if (uid < 0 || uid >= 1'000'000'000)

kernel/kernel/Syscall.cpp

@@ -140,6 +140,9 @@ namespace Kernel
 		case SYS_DUP2:
 			ret = Process::current().sys_dup2((int)arg1, (int)arg2);
 			break;
+		case SYS_RAISE:
+			ret = Process::current().sys_raise((int)arg1, interrupt_stack.rsp, interrupt_stack.rip);
+			break;
 		default:
 			dwarnln("Unknown syscall {}", syscall);
 			break;

kernel/kernel/kernel.cpp

@@ -98,8 +98,8 @@ namespace BAN::Formatter
 
 }
 
-extern "C" uintptr_t g_kernel_start;
-extern "C" uintptr_t g_kernel_end;
+extern "C" uint8_t g_userspace_start[];
+extern "C" uint8_t g_userspace_end[];
 
 static void init2(void*);