How to load an address that was allocated in a separate function using IRBuilder - LLVM 6.0












0















Working on a research project that requires to add load instructions to an analyzed LLVM IR code to load in a function func_A addresses that were allocated in a separate function func_B using IRBuilder. An example is shown as follows.



define void @func_B() {
%1 = alloca [1 x i32], align 4
}

define void @func_A() {
// load the address allocated above here using IRBuilder in an analysis pass
// to the IR code, something like the following:
// IRBuilder<> builder();
// builder.CreateLoad(val);
}


I've been able to find the to-be-loaded llvm:value*, i.e., val in the above example, but the problem is val is a local identifier declared in func_B and may conflict with func_A's identifiers (say func_A declares a local identifier named %1 too) when loaded in func_A.



How can I load func_B's %1 without conflicts in func_A? Note that I can't pass %1 to func_A as a function parameter since I don't want to change anything of the IR code but adding some load instructions.



Any help would be greatly appreciated!










share|improve this question



























    0















    Working on a research project that requires to add load instructions to an analyzed LLVM IR code to load in a function func_A addresses that were allocated in a separate function func_B using IRBuilder. An example is shown as follows.



    define void @func_B() {
    %1 = alloca [1 x i32], align 4
    }

    define void @func_A() {
    // load the address allocated above here using IRBuilder in an analysis pass
    // to the IR code, something like the following:
    // IRBuilder<> builder();
    // builder.CreateLoad(val);
    }


    I've been able to find the to-be-loaded llvm:value*, i.e., val in the above example, but the problem is val is a local identifier declared in func_B and may conflict with func_A's identifiers (say func_A declares a local identifier named %1 too) when loaded in func_A.



    How can I load func_B's %1 without conflicts in func_A? Note that I can't pass %1 to func_A as a function parameter since I don't want to change anything of the IR code but adding some load instructions.



    Any help would be greatly appreciated!










    share|improve this question

























      0












      0








      0








      Working on a research project that requires to add load instructions to an analyzed LLVM IR code to load in a function func_A addresses that were allocated in a separate function func_B using IRBuilder. An example is shown as follows.



      define void @func_B() {
      %1 = alloca [1 x i32], align 4
      }

      define void @func_A() {
      // load the address allocated above here using IRBuilder in an analysis pass
      // to the IR code, something like the following:
      // IRBuilder<> builder();
      // builder.CreateLoad(val);
      }


      I've been able to find the to-be-loaded llvm:value*, i.e., val in the above example, but the problem is val is a local identifier declared in func_B and may conflict with func_A's identifiers (say func_A declares a local identifier named %1 too) when loaded in func_A.



      How can I load func_B's %1 without conflicts in func_A? Note that I can't pass %1 to func_A as a function parameter since I don't want to change anything of the IR code but adding some load instructions.



      Any help would be greatly appreciated!










      share|improve this question














      Working on a research project that requires to add load instructions to an analyzed LLVM IR code to load in a function func_A addresses that were allocated in a separate function func_B using IRBuilder. An example is shown as follows.



      define void @func_B() {
      %1 = alloca [1 x i32], align 4
      }

      define void @func_A() {
      // load the address allocated above here using IRBuilder in an analysis pass
      // to the IR code, something like the following:
      // IRBuilder<> builder();
      // builder.CreateLoad(val);
      }


      I've been able to find the to-be-loaded llvm:value*, i.e., val in the above example, but the problem is val is a local identifier declared in func_B and may conflict with func_A's identifiers (say func_A declares a local identifier named %1 too) when loaded in func_A.



      How can I load func_B's %1 without conflicts in func_A? Note that I can't pass %1 to func_A as a function parameter since I don't want to change anything of the IR code but adding some load instructions.



      Any help would be greatly appreciated!







      llvm llvm-ir






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      asked Nov 16 '18 at 21:39









      RuiRui

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      184
























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          You, obviously, can't do that. It is as if you wanted to access int a from the bar() in the following example:



          int foo()
          {
          int a = 5;
          }

          int bar()
          {
          ...
          }


          Since %1 is allocated on the stack, its memory get freed when the function func_B finishes, so it may not even exist during func_A execution.



          The only thing you can do is to store the value of %1 into a global variable in func_B and load it in func_A:



          @var = [1 x i32] zeroinitializer

          define void @func_B() {
          %1 = alloca [1 x i32], align 4
          store %1, @var
          }

          define void @func_A() {
          // load the address allocated above here using IRBuilder in an analysis pass
          // to the IR code, something like the following:
          // IRBuilder<> builder();
          // builder.CreateLoad(val);
          %1 = load @var
          }





          share|improve this answer























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            1 Answer
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            0














            You, obviously, can't do that. It is as if you wanted to access int a from the bar() in the following example:



            int foo()
            {
            int a = 5;
            }

            int bar()
            {
            ...
            }


            Since %1 is allocated on the stack, its memory get freed when the function func_B finishes, so it may not even exist during func_A execution.



            The only thing you can do is to store the value of %1 into a global variable in func_B and load it in func_A:



            @var = [1 x i32] zeroinitializer

            define void @func_B() {
            %1 = alloca [1 x i32], align 4
            store %1, @var
            }

            define void @func_A() {
            // load the address allocated above here using IRBuilder in an analysis pass
            // to the IR code, something like the following:
            // IRBuilder<> builder();
            // builder.CreateLoad(val);
            %1 = load @var
            }





            share|improve this answer




























              0














              You, obviously, can't do that. It is as if you wanted to access int a from the bar() in the following example:



              int foo()
              {
              int a = 5;
              }

              int bar()
              {
              ...
              }


              Since %1 is allocated on the stack, its memory get freed when the function func_B finishes, so it may not even exist during func_A execution.



              The only thing you can do is to store the value of %1 into a global variable in func_B and load it in func_A:



              @var = [1 x i32] zeroinitializer

              define void @func_B() {
              %1 = alloca [1 x i32], align 4
              store %1, @var
              }

              define void @func_A() {
              // load the address allocated above here using IRBuilder in an analysis pass
              // to the IR code, something like the following:
              // IRBuilder<> builder();
              // builder.CreateLoad(val);
              %1 = load @var
              }





              share|improve this answer


























                0












                0








                0







                You, obviously, can't do that. It is as if you wanted to access int a from the bar() in the following example:



                int foo()
                {
                int a = 5;
                }

                int bar()
                {
                ...
                }


                Since %1 is allocated on the stack, its memory get freed when the function func_B finishes, so it may not even exist during func_A execution.



                The only thing you can do is to store the value of %1 into a global variable in func_B and load it in func_A:



                @var = [1 x i32] zeroinitializer

                define void @func_B() {
                %1 = alloca [1 x i32], align 4
                store %1, @var
                }

                define void @func_A() {
                // load the address allocated above here using IRBuilder in an analysis pass
                // to the IR code, something like the following:
                // IRBuilder<> builder();
                // builder.CreateLoad(val);
                %1 = load @var
                }





                share|improve this answer













                You, obviously, can't do that. It is as if you wanted to access int a from the bar() in the following example:



                int foo()
                {
                int a = 5;
                }

                int bar()
                {
                ...
                }


                Since %1 is allocated on the stack, its memory get freed when the function func_B finishes, so it may not even exist during func_A execution.



                The only thing you can do is to store the value of %1 into a global variable in func_B and load it in func_A:



                @var = [1 x i32] zeroinitializer

                define void @func_B() {
                %1 = alloca [1 x i32], align 4
                store %1, @var
                }

                define void @func_A() {
                // load the address allocated above here using IRBuilder in an analysis pass
                // to the IR code, something like the following:
                // IRBuilder<> builder();
                // builder.CreateLoad(val);
                %1 = load @var
                }






                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered Nov 17 '18 at 8:44









                arrowdarrowd

                22.2k44981




                22.2k44981






























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