Static Program Analysis of Embedded Software
Ramakrishnan Venkitaraman
Graduate Student, Computer Science
Advisor: Dr. Gopal Gupta
Software Reuse & System Integration
But, the Integrated System does not
work
Cost of ProjectCompanies
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.
Why Software Standard?
• Incompatibilities make integration difficult.
• Complexity in software reuse.
• COTS Marketplace.
• Time to Market.
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.
Problem and Solution
• Problem: Detection of hard coded addresses in programs without accessing source code.
• Solution: “Static Program Analysis”
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.
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.
Hard Coded Addresses
• Bad Programming Practice.
• Results in non relocatable code.
• Results in non reusable code.
Overview Of Our Approach
• Input: Object Code of the Software
• Output: Compliant or Not Compliant status
Activity Diagram for our Static Analyzer
Disassemble Object Code
Split Into Functions
Obtain Basic Blocks
Obtain Flow Graph
Static Analysis
Output the Result
Basic Aim Of Analysis
• Find a path to trace pointer origin.
• Problem: Exponential Complexity • Static Analysis approximation makes it linear
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;}
{ { q } }
{ { p } }
P IS HARD CODED
So, the program is not compliant with the standard
Analyzing Assembly – Hard
000007A0 main:000007A0 07BD09C2 SUB.D2 SP,0x8,SP000007A4 020FA02A MVK.S2 0x1f40,B4000007A8 023C22F6 STW.D2T2 B4,*+SP[0x1]000007AC 00002000 NOP 2000007B0 023C42F6 STW.D2T2 B4,*+SP[0x2]000007B4 00002000 NOP 2000007B8 0280A042 MVK.D2 5,B5000007BC 029002F6 STW.D2T2 B5,*+B4[0x0]000007C0 00002000 NOP 2000007C4 008C8362 BNOP.S2 B3,4000007C8 07BD0942 ADD.D2 SP,0x8,SP000007CC 00000000 NOP 000007D0 00000000 NOP
{{ }}
{ { B4 } }
{{ B4 }}
B4 = 0x1f40
So, B4 is HARD CODED
Code is NOT Compliant
Phases In Analysis
• Phase 1: Find the set of dereferenced pointers.
• Phase 2: Check the safety of dereferenced pointers.
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)
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}.
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.
Merging Information
• If no merging, then exponential complexity.
• Mandatory when loops
• Information loss.
If (Cond)
ThenBlock B
ElseBlock C
Block D
Block A
Block E
Extensive Compliance Checking
• Handle all cases occurring in programs.
• Single pointer, double pointer, triple pointer…
• Global pointer variables.
• Static and Dynamic arrays.
Extensive Compliance Checking
• Loops – all forms (e.g. for, while…)
• Function calls.
• Pipelining and Parallelism.
• Merging information from multiple paths.
Analysis Stops when…
• Compliance of all the pointers are established.
• Errors and warnings are reported.
• Log file containing statistics of the analysis is created.
Analysis Results
Program # Lines # * Ptrs # Hard Coded
Chain Length
Running Time (ms)
t_read 80 3 0 0 1280
timer1 126 17 6 1 1441
mcbsp1 196 0 0 0 1270
figtest 292 19 10 2 1521
m_hdrv 345 6 2 1 2262
dat 949 10 8 12 2512
gui_codec 1139 109 28 1 3063
codec 1188 109 28 1 3043
stress 1203 105 0 1 4505
demo 1350 82 47 9 4716
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.
So…
• Hard Coding is a bad programming practice. • Non relocatable/reusable code.
• A Static Analysis based technique is useful and practical.
Software Reuse & System Integration
WOW!!!! It works…
Select ONLY Compliant Software
Questions…
More Information: Ramakrishnan Venkitaraman
[email protected]/~ramakrishnan/
www.utdallas.edu/~gupta/alps/
• Click to continue• Extra slides
General Programming Rules• No tool currently exists to check for
compliance.• SIX rules.
1) All programs should follow the runtime conventions of TI’s C programming language.
2) Algorithms must be re-entrant.
3) No hard coded data memory locations.4) No hard coded program memory locations.
5) Algorithms must characterize their ROM-ability.
6) No peripheral device accesses.
Some examples showing 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
void main(){ int *p, val;
p = ….;val = …;
if(val) p = 0x900;else p = malloc(…);
*p;}
Example3:Conditional Hardcoding
NOTE: We don’t care ifa pointer is hard coded and is never dereferenced.
Sample Code
Fig. Flow Graph