adaslicer: an ada program slicer
DESCRIPTION
AdaSlicer: An Ada Program Slicer. Ricky E. Sward Department of Computer Science USAF Academy, CO [email protected]. A.T. Chamillard Computer Science Department University of Colorado Spring, CO [email protected]. Overview. Background Global Variables Identifying Globals - PowerPoint PPT PresentationTRANSCRIPT
AdaSlicer: An Ada Program SlicerAdaSlicer: An Ada Program Slicer
Ricky E. SwardDepartment of Computer Science
USAF Academy, CO
A.T. ChamillardComputer Science Department
University of Colorado Spring, CO [email protected]
OverviewOverview• Background• Global Variables• Identifying Globals• Annotating Globals• Re-engineering Globals• ASIS• Conclusions
BackgroundBackground
• Identifying global variables is well-defined • Discussed in programming language texts• Tools available to identify global variables• Useful to identify during re-engineering• In SPARK, globals are allowed, must annotate• Goal is to convert to parameters
OverviewOverview• Background• Global Variables• Identifying Globals• Annotating Globals• Re-engineering Globals• ASIS• Conclusions
Global VariablesGlobal Variables
• In Ada, each variable must be declared• Scope defines where a variable is visible
• A and B are local variables
procedure Local is A : Integer := 0; B : Integer := 3; begin A := B * 2;end Local;
Global VariablesGlobal Variables
• A non-local variable is defined outside scope• A global variable is non-local and also visible to
entire programprocedure Outer_Procedure is A : Integer := 0; procedure Inner_Procedure is B : Integer := 1; begin A := A + B; end Inner_Procedure;begin A := A + 1;end Outer_Procedure;
A is global
Global VariablesGlobal Variables• A package variable is in package global scope • A package variable is a “good” global
package One_Global is X : Integer := 10; procedure Outera (A : in out Integer);end One_Global;
package body One_Global is procedure Outera (A : in out Integer) is begin X := X + 1; end Outera;end One_Global;
Package var X
OverviewOverview• Background• Global Variables• Identifying Globals• Annotating Globals• Re-engineering Globals• ASIS• Conclusions
Identifying Global VariablesIdentifying Global Variables
package One_Global is X : Integer := 10; procedure Outera (A : in out Integer);end One_Global;
package body One_Global is procedure Outera (A : in out Integer) is Y : Integer := 0; procedure Innerb (B : in out Integer) is begin B := X; X := X + 1; end Innerb; begin Y := A; Innerb(A); end Outera;end One_Global;
A is a parameter
Y is local
• Using static analysis consider the scope of variables • Ignore local variables and parameters
Identifying Global VariablesIdentifying Global Variables• Using static analysis consider the scope of variables • Ignore local variables and parameters
package One_Global is X : Integer := 10; procedure Outera (A : in out Integer);end One_Global;
package body One_Global is procedure Outera (A : in out Integer) is Y : Integer := 0; procedure Innerb (B : in out Integer) is begin B := X; X := X + 1; end Innerb; begin Y := A; Innerb(A); end Outera;end One_Global;
B is a parameter
X is global
Identifying Global VariablesIdentifying Global Variables• Access declaration information in symbol table• Ok if package variable and procedure in outer scope
package One_Global is X : Integer := 10; procedure Outera (A : in out Integer);end One_Global;
package body One_Global is procedure Outera (A : in out Integer) is Y : Integer := 0; procedure Innerb (B : in out Integer) is begin B := X; X := X + 1; end Innerb; begin Y := A; Innerb(A); end Outera;end One_Global;
Variable Scope Nesting
Y Outera 1
X One_Global 0
... ... ...
Symbol Table
OverviewOverview• Background• Global Variables• Identifying Globals• Annotating Globals• Re-engineering Globals• ASIS• Conclusions
Annotating Global VariablesAnnotating Global Variables• One option in our tool is to add SPARK annotation
--# global <mode> <variable name>;
package One_Global is X : Integer := 10; procedure Outera (A : in out Integer);end One_Global;
package body One_Global is procedure Outera (A : in out Integer) is Y : Integer := 0; procedure Innerb (B : in out Integer) is --# global in out X; begin B := X; X := X + 1; end Innerb; begin Y := A; Innerb(A); end Outera;end One_Global;
package One_Global is X : Integer := 10; procedure Outera (A : in out Integer);end One_Global;
package body One_Global is procedure Outera (A : in out Integer) is Y : Integer := 0; procedure Innerb (B : in out Integer) is --# global in out X; begin B := X; X := X + 1; end Innerb; begin Y := A; Innerb(A); end Outera;end One_Global;
Annotating Global VariablesAnnotating Global Variables
REF set: { B, X }
DEF set: { B, X }
• To determine mode of global, look at DEF and REF
OverviewOverview• Background• Global Variables• Identifying Globals• Annotating Globals• Re-engineering Globals• ASIS• Conclusions
Re-engineering Global VariablesRe-engineering Global Variables• Add global as formal parameter• Add global as actual parameter in call• Use the global definition of the variable to build
the parameter• Use the DEF and REF set to build the mode
– Appears only in REF, build as “in” parameter– Appears only in DEF, build as “out” parameter– Appears in both DEF and REF, build as “in out” using
conservative approach
• For example...
package One_Global_New is X : Integer := 10; procedure Outera (A : in out Integer);end One_Global;
package body One_Global_New is procedure Outera (A : in out Integer) is Y : Integer := 0; procedure Innerb ( B : in out Integer; X : in out Integer ) is begin B := X; X := X + 1; end Innerb; begin Y := A; Innerb(B => A, X => X); end Outera;end One_Global_New;
Re-engineering Global VariablesRe-engineering Global Variables
Add as formal
Add as actual
Re-engineering Global VariablesRe-engineering Global Variables
• What if a global is nested deeper?• May need to change two or more procedures• Add global as formal parameter• Add global as actual parameter• Check to see if actual is global
• For example...
package body Two_Globals is procedure Outera ( A : in out Integer ) is procedure Innerb ( B : in out Integer ) is procedure Innerc ( C : in out Integer ) is begin C := Y; Y := Y + 1; end Innerc; begin B := B + 1; Innerc(C => B); end Innerb; begin Innerb(B => A); end Outera;end Two_Globals;
Re-engineering Global VariablesRe-engineering Global Variables
Y is a global
package body Two_Globals_new is procedure Outera ( A : in out Integer ) is procedure Innerb ( B : in out Integer) is procedure Innerc ( C : in out Integer; Y : in out Integer ) is begin C := Y; Y := Y + 1; end Innerc; begin B := B + 1; Innerc(C => B, Y => Y); end Innerb; begin Innerb(B => A); end Outera;end Two_Globals_new;
Re-engineering Global VariablesRe-engineering Global Variables
Y is a global
Need Y here
package body Two_Globals_new is procedure Outera ( A : in out Integer ) is procedure Innerb ( B : in out Integer; Y : in out Integer) is procedure Innerc ( C : in out Integer; Y : in out Integer ) is begin C := Y; Y := Y + 1; end Innerc; begin B := B + 1; Innerc(C => B, Y => Y); end Innerb; begin Innerb(B => A, Y => Y); end Outera;end Two_Globals_new;
Re-engineering Global VariablesRe-engineering Global Variables
Add Y as formal
Add Y as actual
Add Y as formal
Add Y as actual
OverviewOverview• Background• Global Variables• Identifying Globals• Annotating Globals• Re-engineering Globals• ASIS• Conclusions
Ada Semantic Interface Specification Ada Semantic Interface Specification (ASIS)(ASIS)
• Procedures for accessing Ada program structure• Used ASIS 3.15a1 & GNAT Ada Compiler 3.15a1• Reasonable learning curve• Examples provided with ASIS are great• Very powerful tool
ConclusionsConclusions
• Need to develop a graphical user interface• Target re-engineering efforts• Also automatic refactoring applications