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From: "shafitvm at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/53797] New: Not able to print local variable while debugging at -O0
Date: Thu, 28 Jun 2012 11:33:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53797

             Bug #: 53797
           Summary: Not able to print local variable while debugging at
                    -O0
    Classification: Unclassified
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: shafitvm@gmail.com


I tried debugging the following function with arm,i686 and ppc C and C++
compiler.

void func (int);
int main ()
{
    func (20);
    return 0;
}

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


Invocation line :

g++ main.cpp -g3 -gdwarf-2 --save-temps -dA -o main.elf

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.