Switch to using exceptions for guest exiting

Guest-driven exiting could cause objects left on the heap due to a `std::longjmp` from high up in the host call stack, this has been fixed by introducing `ExitException` which implicitly unrolls the stack with the exception handling mechanism.

app/src/main/cpp/skyline/kernel/svc.cpp

@@ -2,6 +2,7 @@
 // Copyright © 2020 Skyline Team and Contributors (https://github.com/skyline-emu/)
 
 #include <os.h>
+#include <nce.h>
 #include <kernel/types/KProcess.h>
 #include <common/trace.h>
 #include <vfs/npdm.h>
@@ -218,9 +219,7 @@ namespace skyline::kernel::svc {
 
     void ExitProcess(const DeviceState &state) {
         state.logger->Debug("Exiting process");
-        if (state.thread->id)
+        throw nce::NCE::ExitException(true);
-            state.process->Kill(false);
-        std::longjmp(state.thread->originalCtx, true);
     }
 
     constexpr i32 IdealCoreDontCare{-1};
@@ -279,7 +278,7 @@ namespace skyline::kernel::svc {
 
     void ExitThread(const DeviceState &state) {
         state.logger->Debug("Exiting current thread");
-        std::longjmp(state.thread->originalCtx, true);
+        throw nce::NCE::ExitException(false);
     }
 
     void SleepThread(const DeviceState &state) {

app/src/main/cpp/skyline/nce.cpp

@@ -14,6 +14,12 @@
 #include "nce.h"
 
 namespace skyline::nce {
+    NCE::ExitException::ExitException(bool killAllThreads) : killAllThreads(killAllThreads) {}
+
+    const char *NCE::ExitException::what() const noexcept {
+        return killAllThreads ? "ExitProcess" : "ExitThread";
+    }
+
     void NCE::SvcHandler(u16 svcId, ThreadContext *ctx) {
         TRACE_EVENT_END("guest");
 
@@ -42,6 +48,12 @@ namespace skyline::nce {
             }
             abi::__cxa_end_catch(); // We call this prior to the longjmp to cause the exception object to be destroyed
             std::longjmp(state.thread->originalCtx, true);
+        } catch (const ExitException &e) {
+            if (e.killAllThreads && state.thread->id) {
+                signal::BlockSignal({SIGINT});
+                state.process->Kill(false);
+            }
+            std::longjmp(state.thread->originalCtx, true);
         } catch (const std::exception &e) {
             if (svc)
                 state.logger->ErrorNoPrefix("{} (SVC: {})\nStack Trace:{}", e.what(), svc.name, state.loader->GetStackTrace());
@@ -94,7 +106,7 @@ namespace skyline::nce {
                     std::ifstream status("/proc/self/status");
                     constexpr std::string_view TracerPidTag = "TracerPid:";
 
-                    for (std::string line; std::getline(status, line); ) {
+                    for (std::string line; std::getline(status, line);) {
                         if (line.starts_with(TracerPidTag)) {
                             line = line.substr(TracerPidTag.size());
 

app/src/main/cpp/skyline/nce.h

@@ -17,6 +17,21 @@ namespace skyline::nce {
         static void SvcHandler(u16 svcId, ThreadContext *ctx);
 
       public:
+        /**
+         * @brief An exception which causes the throwing thread to exit alongside all threads optionally
+         * @note Exiting must not be performed directly as it could leak temporary objects on the stack by not calling their destructors
+         */
+        struct ExitException : std::exception {
+            bool killAllThreads; //!< If to kill all threads or just the throwing thread
+
+            ExitException(bool killAllThreads = true);
+
+            virtual const char* what() const noexcept;
+        };
+
+        /**
+         * @brief Handles any signals in the NCE threads
+         */
         static void SignalHandler(int signal, siginfo *info, ucontext *ctx, void **tls);
 
         NCE(const DeviceState &state);

app/src/main/cpp/skyline/services/am/controller/ISelfController.cpp

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: MPL-2.0
 // Copyright © 2020 Skyline Team and Contributors (https://github.com/skyline-emu/)
 
+#include <nce.h>
 #include <kernel/types/KProcess.h>
 #include <services/hosbinder/IHOSBinderDriver.h>
 #include "ISelfController.h"
@@ -9,10 +10,7 @@ namespace skyline::service::am {
     ISelfController::ISelfController(const DeviceState &state, ServiceManager &manager) : libraryAppletLaunchableEvent(std::make_shared<type::KEvent>(state, false)), accumulatedSuspendedTickChangedEvent(std::make_shared<type::KEvent>(state, false)), hosbinder(manager.CreateOrGetService<hosbinder::IHOSBinderDriver>("dispdrv")), BaseService(state, manager) {}
 
     Result ISelfController::Exit(type::KSession &session, ipc::IpcRequest &request, ipc::IpcResponse &response) {
-        if (state.thread->id)
+        throw nce::NCE::ExitException(true);
-            state.process->Kill(false);
-        std::longjmp(state.thread->originalCtx, true);
-        return {};
     }
 
     Result ISelfController::LockExit(type::KSession &session, ipc::IpcRequest &request, ipc::IpcResponse &response) {