Implement posix app loading (#643)

- Added POSIX desktop support for SDK builds, application packaging, and integration testing.
- Added POSIX filesystem partitions and improved application path handling.
- Added simulator support for loading and running applications dynamically.
- Improved simulator task stack handling and display startup reliability.
- Improved simulator display scaling, resizing, high-DPI support, and pointer accuracy.
- Fixed LVGL timers and input polling on POSIX. (fixes simulator with Linux on some Intel graphics platforms)
- Standardized data paths across platforms.
- Logging now works via separate task: this allows apps to write to log without it affecting their stdout (for apps that output text as relevant date for other apps, like the File Selection app)
- Fixes for app stdio

Modules/app-posix-module/source/app_posix_loader_service.cpp

@@ -0,0 +1,124 @@
+// SPDX-License-Identifier: Apache-2.0
+#include <app/loader.h>
+#include <app/location.h>
+
+#include <tactility/error.h>
+#include <tactility/log.h>
+
+#include <service/manager.h>
+
+#include <dlfcn.h>
+#include <sys/stat.h>
+
+#include <new>
+#include <string>
+
+constexpr auto* TAG = "app_posix_loader";
+
+namespace {
+
+/** load()-allocated state, passed back through run()/unload(). */
+struct PosixAppRuntime {
+    void* handle = nullptr;
+};
+
+bool is_regular_file(const std::string& path) {
+    struct stat path_stat {};
+    return ::stat(path.c_str(), &path_stat) == 0 && S_ISREG(path_stat.st_mode);
+}
+
+// location.location can be either an app's install directory or the .so file directly; the
+// former resolves to the per-architecture binary at {dir}/elf/posix-{TACTILITY_POSIX_ARCH}.so,
+// mirroring app_esp32_loader_service.cpp's resolve_elf_path().
+error_t resolve_app_path(const std::string& path, std::string& resolvedPath) {
+    if (path.ends_with(".so")) {
+        resolvedPath = path;
+        return ERROR_NONE;
+    }
+    std::string shared_object_path = path + "/elf/posix-" TACTILITY_POSIX_ARCH ".so";
+    if (!is_regular_file(shared_object_path)) {
+        return ERROR_NOT_FOUND;
+    }
+    resolvedPath = shared_object_path;
+    return ERROR_NONE;
+}
+
+error_t api_load(AppLocation location, AppRuntime* out_runtime) {
+    if (location.type != APP_LOCATION_PATH) {
+        LOG_E(TAG, "Unsupported location type");
+        return ERROR_NOT_SUPPORTED;
+    }
+
+    std::string app_path;
+    auto error = resolve_app_path(static_cast<const char*>(location.location), app_path);
+    if (error != ERROR_NONE) {
+        LOG_E(TAG, "Failed to resolve app path: %s", location.location);
+        return error;
+    }
+
+    LOG_I(TAG, "Loading %s", app_path.c_str());
+
+    // RTLD_NOW: a missing symbol fails here, not mid-run(). RTLD_LOCAL: this app's own exported
+    // symbols (if any beyond its entry point) don't leak into the process's global scope and
+    // clash with a different app's.
+    void* handle = dlopen(app_path.c_str(), RTLD_NOW | RTLD_LOCAL);
+    if (handle == nullptr) {
+        LOG_E(TAG, "dlopen(%s) failed: %s", app_path.c_str(), dlerror());
+        return ERROR_NOT_FOUND;
+    }
+
+    auto* runtime = new (std::nothrow) PosixAppRuntime { .handle = handle };
+    if (runtime == nullptr) {
+        LOG_E(TAG, "Out of memory");
+        dlclose(handle);
+        return ERROR_OUT_OF_MEMORY;
+    }
+
+    *out_runtime = runtime;
+    return ERROR_NONE;
+}
+
+int32_t api_run(AppRuntime runtime_ptr, uint32_t /*app_instance_id*/, int argc, char* argv[]) {
+    auto* runtime = static_cast<PosixAppRuntime*>(runtime_ptr);
+
+    dlerror(); // clear any pending error, per dlsym(3)'s own recommended idiom for telling a NULL
+               // symbol address apart from a real lookup failure
+    void* symbol = dlsym(runtime->handle, "main");
+    const char* lookup_error = dlerror();
+    if (symbol == nullptr || lookup_error != nullptr) {
+        LOG_E(TAG, "dlsym(\"main\") failed: %s", lookup_error != nullptr ? lookup_error : "not found");
+        return -1;
+    }
+
+    auto* main_fn = reinterpret_cast<AppMainFn>(symbol);
+    return main_fn(argc, argv);
+}
+
+void api_unload(AppRuntime runtime_ptr) {
+    auto* runtime = static_cast<PosixAppRuntime*>(runtime_ptr);
+    dlclose(runtime->handle);
+    delete runtime;
+}
+
+AppLoaderApi loader_api = {
+    .load = api_load,
+    .run = api_run,
+    .unload = api_unload,
+};
+
+void* create_service(const ServiceManifest*) {
+    return &loader_api;
+}
+
+void destroy_service(const ServiceManifest*, void*) {
+}
+
+} // namespace
+
+ServiceManifest loader_service_manifest = {
+    .id = APP_LOADER_PATH_SERVICE_ID,
+    .create_service = create_service,
+    .destroy_service = destroy_service,
+    .on_start = nullptr,
+    .on_stop = nullptr,
+};