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The Future of Correct Software

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It is estimated that software bugs cost the economy over $60B a year ... Customers still favor features and performance. Programmers notoriously overconfident ... – PowerPoint PPT presentation

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Title: The Future of Correct Software


1
The Future of Correct Software
  • George Necula

2
Software Correctness is Important
  • Where there is software, there are bugs
  • It is estimated that software bugs cost the
    economy over 60B a year (1 of GDP)
  • Average cost of downtime can be 1M/hour
  • Software bugs are responsible for over 50 of
    known security vulnerabilities

3
Software Correctness is Hard
  • Social challenges
  • Customers still favor features and performance
  • Programmers notoriously overconfident
  • Economic challenges
  • Correctness costs more than extra features
  • Technical challenges
  • Impossible to build perfect software quality
    tools
  • False alarms and missed errors are facts of life

4
The Open Source Quality Group
  • Members
  • Rastislav Bodik, George Necula, Sanjit Seshia
  • Collaborators at Stanford, Microsoft, IBM, Intel
  • And 15 graduate students
  • Develop techniques and tools for building,
    deploying and monitoring quality software
  • Use Open Source software as a test bed

5
1. Building Correct Software
  • Tools can help only if we bring more information
    in the software process
  • Find unobtrusive ways to get programmer
    assistance with correctness reasoning
  • Programs express how things must be done
  • Programmers know the what and why !
  • Example Programming by sketching
  • by Rastislav Bodik, Sanjit Seshia

6
The Sketching Experience
sketch
7
Promising Properties
  • Sketched programs are developed
  • rapidly the low-level details are synthesized
    automatically
  • correctly implementation guaranteed to behave
    like the specification

8
Example Sorting by hand
  • int merge (int a, int b, int n)
  • for (int i 0 i lt n i)
  • if ( jltn ( !(kltn) aj lt bk) )
  • resulti aj j
  • else
  • resulti bk k
  • return result
  • The devil is in the details

9
Sorting sketched
  • int merge (int a, int b, int n)
  • for (int i 0 i lt n i)
  • if ( synthesize( , , lt, !, ) )
  • resulti aj j
  • else
  • resulti bk k
  • return result
  • Sketch compiler fills in the details correctly
  • Sketches are programs with missing details
  • Specifications can be slow/simple programs

hole
10
Experience with Sketching Ciphers
  • User experiment
  • goal implement a mini-cipher
  • how C programmer vs. sketching programmer
  • Results
  • sketching programmer was twice as fast
  • sketched cipher ran 50 faster
  • Next sketching for general purpose programs

11
2. Deploying Correct Software
  • Todays view of software
  • Software is executable
  • Future view of software
  • Software is checkable and executable
  • We need to redefine what software is
  • Software Executable content
  • Assurance support

12
Today Digital Signatures
Code
Trust the code producer
  • Not a behavioral assurance
  • Dangerous !
  • Does not scale well
  • Good but not enough

Consumer
13
Future Semantic Assurance
Code
Safety Proof
Code producer helps the consumer to check the
code
Proof Checking
  • Proof-carrying code
  • Provides semantic assurance
  • Producer does the hard work

Consumer
14
Challenges
  • How small can you make the proofs?
  • Today about 25 of the code and shrinking
  • How do you generate proofs ?
  • Certifying software synthesis tools (compilers)
  • Automatic today for memory safety, resource usage
    constraints
  • Next make more software tools certifying

15
3. When Everything Else Fails
  • The future of correct software must include
    incorrect software
  • We must deal with execution errors
  • Monitoring, recovery, restarting,
  • Example Cooperative Bug Isolation

16
Post-Deployment Monitoring
Cooperative Bug Isolation
17
Idea Measure Reality
  • Go beyond measuring crashes
  • Monitor good and bad executions
  • Spread cost of monitoring over many users
  • Collect feedback data mine for bug causes
  • Actual user runs are a vast resource
  • Number of real runs gtgt number of testing runs
  • Real-world executions are most important

18
Bug Isolation Architecture
Sampler
ShippingApplication
ProgramSource
Compiler
StatisticalDebugging
Pro?leJ/L
Top bugs withlikely causes
19
Public Deployment in Progress
  • Applications do have bugs
  • Attract more users for statistical analysis

20
Conclusion
  • Social factors will work in favor of software
    correctness
  • Technology must provide affordable solutions for
    correctness
  • Bring more information into software process
  • Software synthesis from high-level specifications
  • Software distributions with assurance support
  • Good error handling always important
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