Kernel: Call exit_trap in AArch64 restore_context_and_eret

This matches x86_64's behaviour in common_trap_exit. (called from
thread_context_first_enter)
Currently thread_context_first_enter is only called when creating new
processes from scratch, in which case this doesn't change the actual
behaviour. But once thread_context_first_enter is called as part of
execve support, this will ensure the Thread's m_current_trap is set
correctly to the new trap frame.

Kernel/Arch/aarch64/TrapFrame.cpp

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2023, Idan Horowitz <idan.horowitz@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/Arch/Processor.h>
+#include <Kernel/Arch/aarch64/TrapFrame.h>
+#include <Kernel/InterruptDisabler.h>
+
+namespace Kernel {
+
+extern "C" void exit_trap(TrapFrame* trap)
+{
+    return Processor::current().exit_trap(*trap);
+}
+
+}

Kernel/Arch/aarch64/TrapFrame.h

@@ -24,4 +24,6 @@ struct TrapFrame {
     TrapFrame& operator=(TrapFrame&&) = delete;
 };
 
+extern "C" void exit_trap(TrapFrame*) __attribute__((used));
+
 }

Kernel/Arch/aarch64/vector_table.S

@@ -208,5 +208,7 @@ system_error_lower_el:
 
 .global restore_context_and_eret
 restore_context_and_eret:
+    mov x0, sp
+    bl exit_trap
     restore_previous_context
     eret

Kernel/CMakeLists.txt

@@ -471,6 +471,7 @@ elseif("${SERENITY_ARCH}" STREQUAL "aarch64")
         Arch/aarch64/Processor.cpp
         Arch/aarch64/SafeMem.cpp
         Arch/aarch64/SmapDisabler.cpp
+        Arch/aarch64/TrapFrame.cpp
         Arch/aarch64/vector_table.S
     )