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Article - CS258897

ObjectAda sometimes generates invalid code to store a bit field record compoment

Modified: 18-Mar-2017   


Applies To

  • ObjectAda 9.2

Description

  • Values of enumeration types in executable are wrong
  • Record components have the wrong value
  • In some cases, ObjectAda generates the wrong instructions:
    • Record components less than 16 bits that occupy more than one byte of memory
    • Problem seems to occur most frequently if data type is an enumeration type
  • Example of source code that exposes the problem:
  • package bug_pkg is
   type T1 is (e1,e2,e3,e4,e5);
   type rec is record
      b : boolean;
      z : T1;
   end record;
   for rec use record
      b at 0 range 0..5;
      z at 0 range 6..8;
   end record;

   type ptr is access all T1;

   procedure test (r : in out rec; p : ptr; b : boolean);
end;

package body bug_pkg is
   procedure test (r : in out rec; p : ptr; b : boolean) is
   begin
      r := (b,p.all);
   end;
end;
  • Incorrect code generated when compiling source code above:
  • The code generated to store the record component r.z is as follows:
         MOV    BH, [EAX+0]   <--------------- Value loaded into BH
         CMP    BH, 4
         JA     SHORT L7

         SHL    BX, 6     <--  Incorrectly assumes value was loaded into BL
         AND    BX, 448
         AND    WORD PTR [EBP-4], 65087

         OR     [EBP-4], BX ;  DY4
         MOV    EBX, [EBP+8] ;  r
         MOV    CX, [EBP-4] ;  DY4
         MOV    [EBX+0], CX

    ​
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