Re: Debug info issue with DW_TAG_lexical_block ?

[Mohamed Shafi <shafitvm@xxxxxxxxx>]

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http://gcc.gnu.org/ml/gcc-help/2012-06/msg00091.html



On 8 June 2012 16:53, Mohamed Shafi <shafitvm@xxxxxxxxx> wrote:
> Hi,
>
> I tried debugging the following function with arm and native C and C++ compiler.
>
> void func(int in)
> {
>     int a;
>     in++;
>     {
>          int k, j;
>          k = 10;
>          j = k + 44;
>          in = j + 1;
>          a = in;
>     }                  <------      Line 1
>     a = in;
>     a++;
> }           <--------- Line 2
>
> When i try to print the value of 'a' when the execution reaches "line
> 2" i get the message "No symbol "a" in current context.". Here is the
> gdb output:
>
> (gdb) l
> 15                j = k + 44;
> 16                in = j + 1;
> 17                a = in;
> 18           }
> 19           a = in;
> 20           a++;
> 21      }
> 22
> 23      int main()
> 24      {
> (gdb) s
> 21      }
> (gdb) p a
> No symbol "a" in current context.
> (gdb) p in
> $1 = 55
> (gdb)
>
> For the same program i am able to view the value of 'a' if i compile
> this as a C program. This happens because DW_TAG_lexical_block which
> is generated only for in C++ debug info marks the scope of variable
> 'a' between prologue and epilogue of the code. Since the epilogue is
> not present in the scope, the variable cannot be viewed when the
> control reaches the closing brace of the function.
>
> Is this an expected behavior?
> Since in C i can view the variable at the end of the function is not
> logical to have the same behavior for C++ code also?
>
> Regards,
> Shafi