Static Program Analysis of Embedded Software

1. Static Program Analysis of Embedded Software Ramakrishnan Venkitaraman Graduate Student, Computer Science Advisor: Dr. Gopal Gupta

2. Companies Cost of Project Software Reuse & System Integration But, the Integrated System does not work

3. Outline • Importance of Software Standards. • Static Analysis based tool developed by us to enforce software standard compliance. • How the marriage between industry and university research increases software reuse.

4. Why Software Standard? • Incompatibilities make integration difficult. • Complexity in software reuse. • COTS Marketplace. • Time to Market.

5. TI XDAIS Standard • Contains 35 rules and 15 guidelines. • SIX General Programming Rules. • No tool currently exists to check for compliance. • We want to build a tool to ENFORCE software compliance for these rules.

6. Problem and Solution • Problem: Detection of hard coded addresses in programs without accessing source code. • Solution: “Static Program Analysis”

7. Interest in Static Analysis • “We actually went out and bought for 30 million dollars, a company that was in the business of building static analysis tools and now we want to focus on applying these tools to large-scale software systems” • Remarks by Bill Gates, 17th Annual ACM Conference on Object-Oriented Programming, Systems, Languages and Application, November 2002.

8. Static Analysis • Defined as any analysis of a program carried out without completely executing the program. • Un-decidability: Impossible to build a tool that will precisely detect hard coding.

9. Hard Coded Addresses • Bad Programming Practice. • Results in non relocatable code. • Results in non reusable code.

10. Overview Of Our Approach • Input: Object Code of the Software • Output: Compliant or Not Compliant status Obtain Basic Blocks Split Into Functions Disassemble Object Code Output the Result Static Analysis Obtain Flow Graph Activity Diagram for our Static Analyzer

11. Basic Aim Of Analysis • Find a pathto trace pointer origin. • Problem: Exponential Complexity • Static Analysis approximation makes it linear

12. Analyzing Source Code – Easy #include<stdio.h> void main() { int *p, *q; //some code p = (int*)8000; //some code q = p; //some code *q = 5; } So, the program is not compliant with the standard P IS HARD CODED { { p } } { { q } }

13. Analyzing Assembly – Hard {{ }} 000007A0 main: 000007A0 07BD09C2 SUB.D2 SP,0x8,SP 000007A4 020FA02A MVK.S2 0x1f40,B4 000007A8 023C22F6 STW.D2T2 B4,*+SP[0x1] 000007AC 00002000 NOP 2 000007B0 023C42F6 STW.D2T2 B4,*+SP[0x2] 000007B4 00002000 NOP 2 000007B8 0280A042 MVK.D2 5,B5 000007BC 029002F6 STW.D2T2 B5,*+B4[0x0] 000007C0 00002000 NOP 2 000007C4 008C8362 BNOP.S2 B3,4 000007C8 07BD0942 ADD.D2 SP,0x8,SP 000007CC 00000000 NOP 000007D0 00000000 NOP B4 = 0x1f40 So, B4 is HARD CODED Code is NOT Compliant { { B4} } {{ B4 }}

14. Phases In Analysis • Phase 1: Find the set of dereferenced pointers. • Phase 2: Check the safety of dereferenced pointers.

15. Building Unsafe Sets (Phase 1) • The first element is added to the unsafe set during pointer dereferencing. • E.g.If“*Reg” in the disassembled code, the unsafe set is initialized to {Reg}. • ‘N’ Pointers Dereferenced  ‘N’ Unsafe sets • Maintained as SOUS (Set Of Unsafe Sets)

16. Populating Unsafe Sets (Phase 2) • For e.g., if • Reg = reg1 + reg2, the element “Reg” is deleted from the unsafe set, and the elements “reg1”, “reg2”, are inserted into the unsafe set. • Contents of the unsafe set will now become {reg1, reg2}.

17. Handling Loops • Complex:# iterations of loop may not be known until runtime. • Cycle the loop until the unsafe set reaches a “fixed point”. • No new information is added to the unsafe set during successive iterations.

18. Merging Information • If no merging, then exponential complexity. • Mandatory when loops • Information loss. Block A If (Cond) Then Block B Else Block C Block D Block E

19. Extensive Compliance Checking • Handle all cases occurring in programs. • Single pointer, double pointer, triple pointer… • Global pointer variables. • Static and Dynamic arrays.

20. Extensive Compliance Checking • Loops – all forms (e.g. for, while…) • Function calls. • Pipelining and Parallelism. • Merging information from multiple paths.

21. Analysis Stops when… • Compliance of all the pointers are established. • Errors and warnings are reported. • Log file containing statistics of the analysis is created.

22. Analysis Results

23. Current Status and Future Work • Prototype Implementation done • But, context insensitive, intra-procedural • Extend to context sensitive, inter-procedural. • Extend compliance check for other rules.

24. So… • Hard Coding is a bad programming practice. • Non relocatable/reusable code. • A Static Analysis based technique is useful and practical.

25. WOW!!!! It works… Software Reuse & System Integration Select ONLY Compliant Software

26. Questions… More Information: Ramakrishnan Venkitaraman ramakrishnan@student.utdallas.edu www.utdallas.edu/~ramakrishnan/ www.utdallas.edu/~gupta/alps/

27. Click to continue • Extra slides

28. General Programming Rules • No tool currently exists to check for compliance. • SIX rules. • All programs should follow the runtime conventions of TI’s C programming language. • Algorithms must be re-entrant. • No hard coded data memory locations. • No hard coded program memory locations. • Algorithms must characterize their ROM-ability. • No peripheral device accesses.

29. Some examples showing hardcoding void main() { int *p, val; p = ….; val = …; if(val) p = 0x900; else p = malloc(…); *p; } Example3: Conditional Hardcoding void main() { int * p = 0x8800; // Some code *p = …; } Example1: Directly Hardcoded void main() { int *p = 0x80; int *q = p; //Some code *q = …; } Example2: Indirectly Hardcoded NOTE: We don’t care if a pointer is hard coded and is never dereferenced.

30. Sample Code

31. Fig. Flow Graph