[LLVMbugs] [Bug 13317] Debug information for inline constructor not proper.

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=13317

Karthik <karthikthecool at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|INVALID                     |

--- Comment #5 from Karthik <karthikthecool at gmail.com> 2012-07-16 01:32:26 CDT ---
Dear Eric,Douglas
Thanks for the quick reply. I had one quick query.

As Douglas mentioned 'C1' name is the complete object constructor and the 'C2'
name is the base object constructor. But in the example

class Apple
{
public:
 Apple ()
    {
      int b = 0;
    }
};

int
main (void)
{
  Apple b;
  return 0;
}

This class has no base. Why does it have a "complete object constructor" and a
"base object constructor" for each?

This dual emission of constructor results in problem with setting breakpoints
in constructors as we have two info for same location.

For e.g.
In the above code if we run the gdb session as follows-


/opt/home/blitz # gdb a.out 
GNU gdb (Linaro GDB) 7.2-2011.03-0-SLP
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "arm-linux-gnueabi".
For bug reporting instructions, please see:
<http://bugs.launchpad.net/gdb-linaro/>...
Reading symbols from /opt/home/blitz/a.out...done.
(gdb) b main
Breakpoint 1 at 0x83ca: file ./class.cpp, line 13.
(gdb) b 6
Breakpoint 2 at 0x8406: file ./class.cpp, line 6.
(gdb) r
Starting program: /opt/home/blitz/a.out 

Breakpoint 1, main () at ./class.cpp:13
warning: Source file is more recent than executable.
13        Apple a;
(gdb) c
Continuing.

Breakpoint 2, Apple::Apple (this=0xbe811ab8) at ./class.cpp:6
6            int b = 0;
(gdb) bt
#0  Apple::Apple (this=0xbe811ab8) at ./class.cpp:6
#1  0x000083f2 in Apple::Apple (this=0xbe811ab8) at ./class.cpp:7
#2  0x000083d8 in main () at ./class.cpp:13
(gdb) Quit
(gdb) 


In the above session we can find that we had set break point at line 6 and have
not yet reached line 7. But the  bt command when run at line 6 also emits the
wrong info -
#1  0x000083f2 in Apple::Apple (this=0xbe811ab8) at ./class.cpp:7
(line 7 info which comes from C1 constructors prologue_end .loc)

There are few other GDB problems as well when we debug the constructor.


When we looked up we found that the same issue was reported in case of GCC. 
We can refer-

http://stackoverflow.com/questions/6921295/dual-emission-of-constructor-symbols
http://gcc.gnu.org/bugs/#known,

When we checked the same in case of gcc it seems it actually alias the symbols
to the same code for both.
A temporary patch seems to have been given as per
http://sources.redhat.com/ml/gdb/2004-07/msg00163.html

We might need to do something similar in case of clang. Please let us know if
our analysis is correct. 
Thanks

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