fix(libc): run guest exit handlers before the host exit handlers

LibcExit called std::exit, which ran the static destructors of the libraries
before the guest exit handlers. A guest handler that freed memory then locked
a destroyed std::mutex, which throws, and a noexcept guest destructor ended in
std::terminate. The guest handlers now run first, while the library objects
are alive.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

core/libs/prx/libc/CMakeLists.txt

@@ -296,6 +296,10 @@ if(BUILD_TESTING)
         target_include_directories(exception_personality_tests PRIVATE ${LIBS_INCLUDE_DIR})
         target_link_libraries(exception_personality_tests PRIVATE libc)
         add_test(NAME exception_personality COMMAND exception_personality_tests)
+        add_test_executable(guest_exit_order_tests ${LIBS_INCLUDE_DIR}/tests/GuestExitOrder.cpp)
+        target_include_directories(guest_exit_order_tests PRIVATE ${LIBS_INCLUDE_DIR})
+        target_link_libraries(guest_exit_order_tests PRIVATE libc)
+        add_test(NAME guest_exit_order COMMAND guest_exit_order_tests)
         if(NOT APPLE)
             enable_language(C)
             add_test_executable(exception_c_cleanup_tests ${LIBS_INCLUDE_DIR}/tests/ExceptionCCleanup.cpp ${LIBS_INCLUDE_DIR}/tests/ExceptionCCleanup.c)

core/libs/prx/libc/src/Process.cpp

@@ -113,6 +113,7 @@ extern "C" {
     exitRequested.store(true);
     if (exitStarted.exchange(true)) LibcAwaitExit_nid_postfix();
     LibcRunShutdown_nid_postfix();
+    CxaFinalize_nid_no_patch(nullptr);
     std::exit(code);
 }
 

core/libs/tests/GuestExitOrder.cpp

@@ -0,0 +1,53 @@
+#include "prx/libc/include/Shutdown.hpp"
+#include "prx/libc/include/general/VabiMacros.hpp"
+#include <cstdio>
+#include <cstdlib>
+#include <sys/wait.h>
+#include <unistd.h>
+
+extern "C" int APS5_VABI __cxa_atexit_nid_postfix(void (APS5_VABI *func)(void*), void* arg, void* dsoHandle);
+
+namespace {
+
+int events[2];
+
+void Record(char value) {
+    static_cast<void>(!write(events[1], &value, 1));
+}
+
+void APS5_VABI GuestHandler(void*) { Record('G'); }
+
+void HostHandler() { Record('H'); }
+
+bool GuestHandlersRunFirst() {
+    if (pipe(events) != 0) return false;
+    const pid_t child = fork();
+    if (child < 0) return false;
+    if (child == 0) {
+        close(events[0]);
+        __cxa_atexit_nid_postfix(GuestHandler, nullptr, nullptr);
+        std::atexit(HostHandler);
+        LibcExit_nid_no_patch(0);
+    }
+    close(events[1]);
+    char order[3] = {};
+    ssize_t length = 0;
+    while (length < 2) {
+        const ssize_t count = read(events[0], order + length, 2 - length);
+        if (count <= 0) break;
+        length += count;
+    }
+    close(events[0]);
+    int status = 0;
+    return waitpid(child, &status, 0) == child && WIFEXITED(status) && WEXITSTATUS(status) == 0 && length == 2 && order[0] == 'G' && order[1] == 'H';
+}
+
+}
+
+int main() {
+    if (!GuestHandlersRunFirst()) {
+        std::fputs("guest exit handlers must run before the host exit handlers\n", stderr);
+        return 1;
+    }
+    return 0;
+}