Miguel Masmano

TLSF: a new dynamic memory allocator for real-time systems

Dynamic storage allocation (DSA) algorithms play an important role in the modern software engineering paradigms and techniques (such as object oriented programming). Using DSA increases the flexibility and functionalities of applications. There exists a large number of references to this particular issue in the literature. However, the use of DSA has been considered a source of indeterminism in the real-time domain, due to the unconstrained response time of DSA algorithms and the fragmentation problem. Nowadays, real-time applications require more flexibility: the ability to adjust system configuration in response to workload changes and application reconfiguration. This aspect adds value to the definition and implementation of dynamic storage allocation algorithms. Considering these reasons, DSA algorithms with a bounded and acceptable timing behaviour must be developed to be used by real-time operating systems (RTOSs). In this paper a DSA algorithm called two-level segregated fit memory allocator (TLSF), developed specifically to be used by RTOS, is introduced. The TLSF algorithm provides explicit allocation and deallocation of memory blocks with a temporal cost /spl Theta/(1).

A constant-time dynamic storage allocator for real-time systems

Dynamic memory allocation has been used for decades. However, it has seldom been used in real-time systems since the worst case of spatial and temporal requirements for allocation and deallocation operations is either unbounded or bounded but with a very large bound.In this paper, a new allocator called TLSF (Two Level Segregated Fit) is presented. TLSF is designed and implemented to accommodate real-time constraints. The proposed allocator exhibits time-bounded behaviour, O(1), and maintains a very good execution time. This paper describes in detail the data structures and functions provided by TLSF. We also compare TLSF with a representative set of allocators regarding their temporal cost and fragmentation.Although the paper is mainly focused on timing analysis, a brief study and comparative analysis of fragmentation incurred by the allocators has been also included in order to provide a global view of the behaviour of the allocators.The temporal and spatial results showed that TLSF is also a fast allocator and produces a fragmentation close to that caused by the best existing allocators.

Dynamic Memory Management for Embedded Real-Time Systems

Dynamic memory storage has been widely used during years in computer science. However, its use in real-time systems has not been considered as an important issue because the spatial and temporal worst case for allocation and deallocation operations were unbounded or bounded but with a very large bound.

ORK+/XtratuM: an open partitioning platform for Ada

The ARINC 653 standard defines an Integrated Modular Avionics (IMA) architecture for building complex systems consisting of several real-time applications with different levels of criticality running in the same hardware platform. Applications execute in partitions that are isolated from each other in the temporal and spatial (i.e. storage) domains. The standard defines an architecture and an applications program interface (API) for an operating system or application executive (APEX) supporting these concepts. This paper describes an implementation of a partitioning platform for Ada based on a similar approach. The platform is built with two components: the XtratuM hypervisor, which supports multiple virtual machines on a single computer, and the Open Ravenscar Kernel (ORK+), a small, reliable real-time kernel supporting the Ada Ravenscar tasking profile. This combination provides an open-source platform that enables highintegrity Ada applications to share the same computer board with other, possibly less critical, applications.

XtratuM hypervisor redesign for LEON4 multicore processor

XtratuM is an open source hypervisor that uses para-virtualization techniques designed to comply with safety critical real-time requirements. Several projects aimed to define a reference architecture for space on-board systems have adopted XtratuM as a virtualization layer in order to enforce the strong spatial and temporal isolation between software components that is required on real-time airborne systems. Given the shift in the general trend in processor development towards multicore processors, the European Space Agency (ESA) is commissioning a set of studies in order to evaluate their suitability for their use on the space market. This paper focuses on the porting of XtratuM to the LEON4 multicore processor, in the frame of a ESA study that pursues to assess its fitness for its use in future space missions.

Memory Resource Management for Real-Time Systems

Dynamic memory storage has been widely used for years in computer science. However, its use in real-time systems has not been considered as an important issue, and memory management has not receive much consideration, whereas todays real-time applications are often characterized by highly fluctuating memory requirements. In this paper we present an approach to dynamic memory management for real-time systems. In response to application behavior and requests, the underlying memory management system adjusts resources to meet changing demands and user needs. The architectural framework that realizes this approach allows adaptive allocation of memory resources to applications involving both periodic or aperiodic tasks. Simulation results demonstrate the suitability of the proposed mechanism.

Running Ada on real-time linux

The Real-Time Linux operating system (RTLinux) is an attractive platform for real-time programming, since real-time tasks can be guaranteed bounded response times, whilst a number of applications, IDEs, GUIs, etc. are also available for the same platform. In RTLinux, real-time tasks are implemented (in C) as kernel modules. Special care must be taken when writing kernel modules: an error in a single task can make the whole system hang or crash, since they are executed in the kernel memory space. This is clearly an area where Ada can be of great help: Adas strong typing, consistency checking, robust syntax and readability, and the availability of high quality compilers, encourage the writing of correct software and allow to catch coding errors early in the implementation. In this paper, we show the state of development of a compilation system for Ada programs on RTLinux, based on the GNAT Ada compiler.

Detecting Stack Based Kernel Information Leaks

The Linux kernel has become widely adopted in the mobile devices and cloud services, parallel to this has grown its abuse and misuse by attackers and malicious users. This has increased attention paid to kernel security through the deployment of kernel protection mechanisms. Kernel based attacks require reliability, kernel attack reliability is achieved through the information gathering stage where the attacker is able to gather enough information about the target to succeed. The taxonomy of kernel vulnerabilities includes information leaks, that are a class of vulnerabilities that permit access to the kernel memory layout and contents. Information leaks can improve the attack reliability allowing the attacker to read sensitive kernel data to bypass kernel based protections.

Multicore partitioned systems based on hypervisor

Abstract Multi-core processors are increasingly being considered to provide the performance required by future safety critical systems. In some domains like space, it is specially significant due to the processor technology frequency is limited by the presence of radiation. In that case, the way to increase computing power can be achieved by the use of multi-core systems. There is a number of challenges involved in the migration to multi-core processor architectures in safety-critical embedded systems domain which are still unresolved and which contribute to increase the complexity of the design. Even if multi-core processors may offer several benefits to embedded systems, their use is not straightforward. Virtualization techniques maturity have reach the level to offer guarantees in critical systems. In this paper, we present a multi-core hypervisor for mixed-criticality applications as one of the results of the MultiPARTES project. The paper analyse the design and implementation of XtratuM for multi-core and details a performance analysis to determine the overheads incurred by the virtualization layer and presents some results when shared resources are considered.

Enforcing trust in control automotive platforms

Trusted computing is a main concern for ensuring that the platform is secure and dependable. This paper will study AUTOSAR regarding to this area and will propose some suggestions to enforce trust in control automotive platforms.