strace: Create a status_t type handler and use it for return values.

This way, we save 3 string comparisons on every non-empty return value.

Actually this code was broken before, and did not print error names
for return types other than status_t, because message.return_value
is an unsigned integer and thus "< 0" was always false. Now we cast
appropriately in the new TypeHandler, so this works properly.

src/bin/debug/strace/TypeHandler.cpp

@@ -91,6 +91,39 @@ TypeHandlerFactory<bool>::Create()
 	return new TypeHandlerImpl<bool>();
 }
 
+// status_t
+class StatusTypeHandler : public TypeHandler {
+public:
+	StatusTypeHandler() {}
+
+	string GetParameterValue(Context &context, Parameter *, const void *address)
+	{
+		return RenderValue(context, get_value<status_t>(address));
+	}
+
+	string GetReturnValue(Context &context, uint64 value)
+	{
+		return RenderValue(context, value);
+	}
+
+private:
+	string RenderValue(Context &context, uint64 value) const
+	{
+		string rendered = context.FormatUnsigned(value);
+		if (value <= UINT32_MAX && (status_t)value <= 0) {
+			rendered += " ";
+			rendered += strerror(value);
+		}
+		return rendered;
+	}
+};
+
+TypeHandler *
+create_status_t_type_handler()
+{
+	return new StatusTypeHandler;
+}
+
 // read_string
 static
 string

src/bin/debug/strace/TypeHandler.h

@@ -97,6 +97,7 @@ struct TypeHandlerFactory {
 
 extern TypeHandler *create_pointer_type_handler();
 extern TypeHandler *create_string_type_handler();
+extern TypeHandler *create_status_t_type_handler();
 
 // specialization for "const char*"
 template<>

src/bin/debug/strace/strace.cpp

@@ -265,10 +265,21 @@ patch_syscalls()
 	// instead of having this done here manually we should either add the
 	// patching step to gensyscalls also manually or add metadata to
 	// kernel/syscalls.h and have it parsed automatically
+
 	extern void patch_fcntl();
 	extern void patch_ioctl();
 	extern void patch_area();
 
+	for (size_t i = 0; i < sSyscallVector.size(); i++) {
+		Syscall *syscall = sSyscallVector[i];
+		const string returnTypeName = syscall->ReturnType()->TypeName();
+		// patch return type handlers
+		if (returnTypeName == "status_t" || returnTypeName == "ssize_t"
+				|| returnTypeName == "int") {
+			syscall->ReturnType()->SetHandler(create_status_t_type_handler());
+		}
+	}
+
 	patch_fcntl();
 	patch_ioctl();
 	patch_area();
@@ -455,21 +466,12 @@ print_syscall(FILE *outputFile, Syscall* syscall, debug_post_syscall &message,
 					syscall->Name().c_str() + 6);
 			}
 		}
+
 		Type *returnType = syscall->ReturnType();
 		TypeHandler *handler = returnType->Handler();
 		::string value = handler->GetReturnValue(ctx, message.return_value);
-		if (value.length() > 0) {
+		if (value.length() > 0)
 			print_to_string(&string, &length, " = %s", value.c_str());
-
-			// if the return type is status_t or ssize_t, print human-readable
-			// error codes
-			if (returnType->TypeName() == "status_t"
-				|| ((returnType->TypeName() == "ssize_t"
-						|| returnType->TypeName() == "int")
-					&& message.return_value < 0)) {
-				print_to_string(&string, &length, " %s", strerror(message.return_value));
-			}
-		}
 	}
 
 	// print arguments