Compositional correctness of IP-based system design: Translating C/C++ Models into SIGNAL Processes Rennes, November 04, 2005 Hamoudi Kalla and Jean-Pierre Talpin Espresso Team

2 Outline Introduction Preliminaries Translating C/C++ Models into SIGNAL Processes  Principles  Example  Implementation Conclusion and Future works

3  Simulators and test tools  They may not cover all design errors  We need formal verification to ensure the quality of system designs  we need formal models C/C++ System Design Validation Introduction

4 System Design Validation Using Formal Models Our Methodology C/C++ Models Formal Models : SIGNAL processes automatic translation

5 Control Data-Flow Graph (CDFG) Single Statement Assignment (SSA) Preliminaries

6  Represents a procedure or a program as a directed graph G=(V, E), where the set V represents control flow nodes and E represents jumps in the control flow  Control Flow nodes are Basic blocks, Test blocks, and Join Blocks Control Data Flow Graph

7 int example(int a, int b, int c) { int x, y, z, result; y = a * b; z = a * c; if (y>z) x = y – z; else x = z – y; result = x * a; return result; } Preliminaries Control Data Flow Graph: Nodes C/C++ program CDFG

8  Basic Blocks (BB) are instructions without any jumps.  Test blocks (T) describe conditional branching expressions.  Join blocks (J) represent the end of conditional branches. Preliminaries Control Data Flow Graph: Nodes CDFG

9  SSA is a form of Control Data Flow Graph that allows optimizations to be done efficiently and easily  In SSA, every variable receives exactly one assignment during its lifetime Preliminaries Single Statement Assignment (SSA) Form … x = a * b; x = a * c; … x1 = a * b; x2 = a * c; … SSA

10 Control Data Flow Graph its associated Static Single Assignment form Preliminaries Single Statement Assignment (SSA) Form New function

11 Translating C/C++ Models into SIGNAL Processes C/C++ Models SIGNAL processes SSA Form GCC ?

12 Translating C/C++ Models into SIGNAL Processes C/C++ Models SIGNAL processes GCC f 1, …, f n functions f 1  SSA 1 f n  SSA n SSA 1  process 1 SSA n  process n … … … ?

13 Translating C/C++ Models into SIGNAL Processes Function f (SSA) Process f (SIGNAL) Encode nodes, edges, assignment statement, conditional branching, and Ф function Principle

14 Encoding SSA Nodes (blocks) Translating C/C++ Models into SIGNAL Processes Boolean BB1, T2, BB2, BB3, J1, BB4; x t1 t2 t3 t4 t5 … BB1 true false false false false … T2 false true false false false … BB2 false false true false false … BB3 false false false true false … J1 false false false false true … BB4 false false false false true … t1 t2 t3 t4 t5 … BB1 true false false false false … T2 false true false false false … BB2 false false true false false … BB3 false false false true false … J1 false false false false true … BB4 false false false false true … Instants blocks

15 Translating C/C++ Models into SIGNAL Processes B1 B2 | B2 : = true when pre_B1 default false | pre_B1 : = B1$ init false t1 t2 t3 t4 t5 … B1 true false false false false … pre_B1 false true false false false … B2 false true false false false … t1 t2 t3 t4 t5 … B1 true false false false false … pre_B1 false true false false false … B2 false true false false false … Encoding SSA Edges : for Basic and Test blocks

16 Translating C/C++ Models into SIGNAL Processes Encoding SSA Edges : for Join blocks J1 B1 | J1 : = true when pre_B1 default true when pre_B2 default false t1 t2 t3 t4 t5 … pre_B2 false true false false false … pre_B1 false false false false false … J1 false false true false false … t1 t2 t3 t4 t5 … pre_B2 false true false false false … pre_B1 false false false false false … J1 false false true false false … B2

17 Translating C/C++ Models into SIGNAL Processes Encoding Assignment Statement t1 t2 t3 t4 t5 … B1 false true false false false false … Pre_B1 false false true false false false … x … y … z … t1 t2 t3 t4 t5 … B1 false true false false false false … Pre_B1 false false true false false false … x … y … z … X1 = y1 + z1 B1 | x1 : = ( y1 + z1 ) when B1 default x1$

18 Translating C/C++ Models into SIGNAL Processes Encoding Conditional Branching Statement If (x>y) goto B1; else goto B2; If (x>y) goto B1; else goto B2; T1 B1 | test1 : = (x>y) when T1default false | pre_test1 : = test1$ init false t1 t2 t3 t4 t5 … T1 false true false false false … pre_T1 false false true false false … Test1 false true false false false … pre_test1 false false true false false … B1 false false true false false … B2 false false false false false … t1 t2 t3 t4 t5 … T1 false true false false false … pre_T1 false false true false false … Test1 false true false false false … pre_test1 false false true false false … B1 false false true false false … B2 false false false false false … B2 | B1 : = true when pre_test1 when pre_T1 default false | B2 : = true when not pre_test1 when pre_T1 default false

19 Translating C/C++ Models into SIGNAL Processes Encoding Ф Function X3 = Ф(x1,x2) J1 B1 | x3 : = x1 when pre_B1 default x2 X1 = … X2 = … B2 Y = x3 + … B3

20 Translating C/C++ Models into SIGNAL Processes Encoding Loop Statement : Blocks If (x>y) goto B1; else goto B2; If (x>y) goto B1; else goto B2; T1 B2 | test1 : = (x>y) when T1default false | pre_test1 : = test1$ init false … … … … B1 … … B0 … … J1 | T1 : = true when pre_B0 default true when pre_B1 default false | B1 : = true when pre_test1 when pre_T1 default false | B2 : = true when not pre_test1 when pre_T1 default false

21 Translating C/C++ Models into SIGNAL Processes Encoding Loop Statement : statements If (i2<10) goto B1; else goto B2; If (i2<10) goto B1; else goto B2; T1 B2 | i1 : = 1 when B0 default i1$ … … i3 := i2 + 1 B1 i1 := 1 B0 i2 := Ф(i1,i3) J1 | i2 : = i1 when pre_B0 default i3 | i3 : = i2$ +1 when pre_B1 default i3$

22 Translating C/C++ Models into SIGNAL Processes Encoding pointers (1) x = 10; if (T) p = &x ; else p = &y ; z = *p; SSA If (T) goto B1; else goto B2; If (T) goto B1; else goto B2; T1 B1 p1 = &x p2 = &y B2 X = 10 B0 p3 = Ф(p1,p2) J1 z = *p3 B3 Signal p = (p_tag,p_star) p_tag = 0  p = &x p_start = x p_tag = 1  p = &y p_start = y

23 Translating C/C++ Models into SIGNAL Processes Encoding pointers (2) If (T) goto B1; else goto B2; If (T) goto B1; else goto B2; T1 B1 p1 = &x p2 = &y B2 X = 10 B0 p3 = Ф(p1,p2) J1 z = *p3 B3 p1 = (p1_tag,p1_star) p1_tag = 0  p1 = &x p1_star = x p2 = (p2_tag,p2_star) p2_tag = 1  p2 = &y p2_star = y p3 = (p3_tag,p3_star) p3_tag = p1_tag U p2_tag p3_star = Ф (p1_start,p2_star) | z : = p3_start when B3 | p3_star : = x when (p3_tag=0) default y when (p3_tag=1)

24 Translating C/C++ Models into SIGNAL Processes Implementation

25  A methodology to validate C/C++ system design :  Extend this work in order to: encode arrays, pointers and functions calls, remove global synchronisation, reduce the number of variables/signals. it automatically creates formal models from C/C++ system models, it is based on the internal representation SSA of GCC and uses the synchronous language SIGNAL as a formal platform. Conclusion and Future Works