Memory overflow protection for embedded systems using run-time checks, reuse, and compression

Abstract

Out-of-memory errors are a serious source of unreliability in most embedded systems. Applications run out of main memory because of the frequent difficulty of estimating the memory requirement before deployment, either because it depends on input data, or because certain language features prevent estimation. The typical lack of disks and virtual memory in embedded systems has two serious consequences when an out-of-memory error occurs. First, there is no swap space for the application to grow into, and the system crashes. Second, since protection from virtual memory is usually absent, the fact that a segment has exceeded its bounds is not even detected and hence no pre-crash remedial action is possible.This work improves system reliability in two ways. First it proposes a low-overhead system of run-time checks by which the outof-memory errors are detected just before they will happen, by using carefully optimized compiler-inserted run-time check code. Such error detection enables the designer to incorporate systemspecific remedial action, such as transfer to manual control, shutting down of non-critical tasks, or other actions. Second, this work proposes five related techniques that can grow the stack or heap segment after it is out of memory, into previously un-utilized space such as dead variables and space freed by compressed live variables. These techniques can avoid the out-of-memory error if the extra space recovered is enough to complete execution.Results from our benchmarks show that the overheads from the system of run-time checks for detecting memory overflow are extremely low: the run-time and code-size overheads are 1.1% and 0.09% on average. When the reuse functionality is included, the run-time and code-size overheads increase to only 3.2% and 2.33%, but the method is able to grow the stack or heap beyond its overflow by an amount that ranges from 0.7% to 93.5% of the combined stack and heap size.

A Dynamic Control Mechanism of Interrupt Stack Overflow on Real‐Time Embedded Monitor (REMON)

“…There are various methods for the detection and prevention of SOF in embedded systems. For example, software for dynamic overflow checking is incorporated when applications are compiled [17], return addresses and pointers are rewritten in advance [18,19], and hardware such as MPUs (memory protection unit, ARM-specific hardware) or MMUs is employed [20][21][22][23].…”

“…Since embedded systems are not usually provided with overflow detection functions and swap areas, memory overflow cannot be dealt with by using virtual memory. Thus, memory overflow protection is provided in which overflow detection software is incorporated into application software at compile time [17].…”

“…A comparison between the proposed method and previous methods is given in Table 1. In the case of memory overflow protection [17], stack-guard [18], and dynamic buffer overflow detector [19] with a check code incorporated into applications, the source code is required; in addition, these methods assume explicit use of memory by applications, and do not aim at detection of overflow in stacks used implicitly, as in the case of function calls.…”

Offline compression for on-chip ram

“…The constrained nature of RAM in embedded systems is well known and a number of research efforts have addressed this problem using online schemes that dynamically recover unused or poorly used space. Biswas et al [7] and Middha et al [19] use compiler-driven techniques to blur the lines between different storage regions. This permits, for example, stacks to overflow into unused parts of the heap, globals, or other stacks.…”

“…Our work targets legacy C code and reduces RAM requirements automatically and transparently. Compile-time predictability rules out online RAM compression, a family of techniques that find and exploit redundant data as a system executes [7,32].…”