Improve error checking on game launch.

See #21886

Core/FileLoaders/LocalFileLoader.cpp

@@ -72,10 +72,10 @@ LocalFileLoader::LocalFileLoader(const Path &filename)
 			return;
 		}
 		fd_ = fd;
-		isOpenedByFd_ = true;
 		DetectSizeFd();
 		return;
 	}
+	// else, fall through to normal file loading (legacy build, old Android etc).
 #endif
 
 #if defined(HAVE_LIBRETRO_VFS)
@@ -153,20 +153,13 @@ bool LocalFileLoader::Exists() {
 	// If we opened it for reading, it must exist.  Done.
 #if defined(HAVE_LIBRETRO_VFS)
 	return file_ != nullptr;
+#elif PPSSPP_PLATFORM(IOS)
+	return fd_ != -1;
 #elif !defined(_WIN32)
-	if (isOpenedByFd_) {
-		// As an optimization, if we already tried and failed, quickly return.
-		// This is used because Android Content URIs are so slow.
-		return fd_ != -1;
-	}
-	if (fd_ != -1)
-		return true;
+	return fd_ != -1;
 #else
-	if (handle_ != INVALID_HANDLE_VALUE)
-		return true;
+	return handle_ != INVALID_HANDLE_VALUE;
 #endif
-
-	return File::Exists(filename_);
 }
 
 bool LocalFileLoader::IsDirectory() {
@@ -182,8 +175,9 @@ s64 LocalFileLoader::FileSize() {
 }
 
 size_t LocalFileLoader::ReadAt(s64 absolutePos, size_t bytes, size_t count, void *data, Flags flags) {
-	if (bytes == 0)
+	if (bytes == 0) {
 		return 0;
+	}
 
 	if (filesize_ == 0) {
 		ERROR_LOG(Log::FileSystem, "ReadAt from 0-sized file: %s", filename_.c_str());

Core/FileLoaders/LocalFileLoader.h

@@ -53,5 +53,4 @@ private:
 	u64 filesize_ = 0;
 	Path filename_;
 	std::mutex readLock_;
-	bool isOpenedByFd_ = false;
 };

Core/FileSystems/BlockDevices.cpp

@@ -222,7 +222,7 @@ static bool FindUDFLayerFileEntrySectors(FileLoader *fileLoader, u32 rootSector,
 BlockDevice *ConstructBlockDevice(FileLoader *fileLoader, std::string *errorString) {
 	if (!fileLoader->Exists()) {
 		// Shouldn't get here really.
-		*errorString = "File doesn't exist";
+		*errorString = "File not readable or doesn't exist";
 		return nullptr;
 	}
 	if (fileLoader->IsDirectory()) {
@@ -230,12 +230,16 @@ BlockDevice *ConstructBlockDevice(FileLoader *fileLoader, std::string *errorStri
 		*errorString += fileLoader->GetPath().ToString();
 		return nullptr;
 	}
+	if (fileLoader->FileSize() < 8) {
+		*errorString = "File is too small to read the header.";
+		return nullptr;
+	}
 
 	char buffer[8]{};
 	size_t size = fileLoader->ReadAt(0, 1, 8, buffer);
 	if (size != 8) {
 		// Bad or empty file
-		*errorString = "File is empty";
+		*errorString = "Failed to read 8-byte header";
 		return nullptr;
 	}
 

Core/Loaders.h

@@ -77,7 +77,7 @@ public:
 	virtual bool IsRemote() {
 		return false;
 	}
-	virtual bool Exists() = 0;
+	virtual bool Exists() = 0;  // This is permitted to essentially be "IsReadable" and not actually report existence (let's say the permissions are wrong, for example...)
 	virtual bool ExistsFast() {
 		return Exists();
 	}

GPU/Common/ShaderUniforms.h

@@ -53,8 +53,8 @@ R"(  mat4 u_proj;
   mat3x4 u_world;
   mat3x4 u_texmtx;
   vec4 u_xywh;
-  vec3 u_vpScale; float u_NaN; // w = offsetX
-  vec4 u_vpOffset; // w = offsetY
+  vec3 u_vpScale; float u_NaN;
+  vec4 u_vpOffset;
   vec2 u_rasterOffset; vec2 u_minZmaxZ;
   vec4 u_uvscaleoffset;
   vec4 u_matambientalpha;