[Bug debug/33044] New: Local variables in C++ constructor not visible for debugging

[Bug debug/33044] New: Local variables in C++ constructor not visible for debugging

[seppo at totalviewtech dot com]

SUMMARY:
In gcc 3.2.3 (and other versions) the DWARF information created by gcc does not
create DW_AT_location attribute for local (static) variables inside a C++
constructor.

WHAT::

The reproducer below shows TWO problems related to debug information available
regarding variables inside a C++ a constructor. One type is (1) a local
variable inside a constructor and second type is (2) a local _static_ variable
inside a constructor. Sometimes TV is able to see the case (1) but only in the
Program Browser (PB); but case (2) is never correctly shown in TV, neither when
Diving, Stack Frame or in PB. 

For some versions of gcc TV can show type (1) in the PB, but for all gcc
versions TV fails to show type (2) at all. 

This problem is not related to TV alone, GDB fails to see these variables as
well.

On gcc 3.2.3, TV can see type (1) only in PB, but type (2) is
not visible to TV at all (only in symtable).

With PGI-7.0.5 (and some other non-gcc compilers) TV can see everything
alright.


REPRODUCE/TEST::

See attached c++ file.

dbreak 25
drun
dprint iii 
dprint foofoo


WHY::

In some gcc versions there is no DWARF information whatsoever related to types
(1) and (2).

In gcc 3.2.3 (and others, e.g. 4.0.3) the DWARF information created by gcc does
not create DW_AT_location attribute for neither type (1) and (2), e.g.

less tx_local.gcc3.2.3.txt
 <2><1760>: Abbrev Number: 41 (DW_TAG_variable)
     DW_AT_name        : foofoo
     DW_AT_decl_file   : 1
     DW_AT_decl_line   : 28
     DW_AT_type        : <178a>

less tx_local.pgi7.0.5.txt
 <1><1048>: Abbrev Number: 14 (DW_TAG_variable)
     DW_AT_name        : foofoo
     DW_AT_type        : <1864>
     DW_AT_location    : 5 byte block: 3 30 e0 4 8      (DW_OP_addr: 804e030; )

Therefore TV (or gdb) does not have enough information to resolve these
variables. 

These variables do exist in the symtable, e.g.:

d1.<> sgrep foofoo
{kind loader_symbol} {id 1|795} {full_pathname
##/nfs/netapp0/user/home/seppo/tx_local.out_gcc3.2.3#tx_local_var_cpp_constructor.cxx/_ZZN1AC1Eii\
E6foofoo} {artificial 0} {scope_owner 1|220} {loader_name _ZZN1AC1EiiE6foofoo}
\
{loader_file_path tx_local_var_cpp_constructor.cxx} {location {{ldam
0x900007a0\
}}} {address_class module_static_var} {length 96} {weak 0}

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

#include <stdio.h>
class A {
public:
  A (int a, int b);
  int a_;
  int b_;
  int c_;
};

A::A (int a, int b) : a_ (a), b_ (b), c_ (0)
{
  int iii;
  iii = 42;
  c_ = a_ * b_;
  c_ += iii;
  static const int foofoo[6][4] = { {0,1,2,3},
                                    {1,2,3,4},
                                    {2,3,4,5},
                                    {3,4,5,6},
                                    {4,5,6,7},
                                    {5,6,7,8} };

  printf("c_ = %d\n", c_);
  printf("foofoo = %d\n", foofoo);
}

int main (int, char* *)
{
  int a = 34, b = 56;
  A x (a, b);
  return x.a_ + x.b_;
}

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX


-- 
           Summary: Local variables in C++ constructor not visible for
                    debugging
           Product: gcc
           Version: 3.2.3
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: debug
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: seppo at totalviewtech dot com
 GCC build triplet: linux-x86 (2.6.16.13-4-smp)


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

[Bug debug/33044] Local variables in C++ constructor not visible for debugging

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|critical                    |normal


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

[Bug debug/33044] Local variables in C++ constructor not visible for debugging

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2007-08-10 21:13 -------
The mainline produces:
        .ascii "foofoo\0"       # DW_AT_name
        .byte   0x1     # DW_AT_decl_file (t.cc)
        .byte   0x10    # DW_AT_decl_line
        .long   0x282   # DW_AT_type
        .byte   0x5     # DW_AT_location
        .byte   0x3     # DW_OP_addr
        .long   __ZZN1AC1EiiE6foofoo

Which is correct.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

[Bug debug/33044] Local variables in C++ constructor not visible for debugging

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2007-08-10 21:15 -------
4.1.0 produces:
        .uleb128 0xd    # (DIE (0x185) DW_TAG_variable)
        .ascii "foofoo\0"       # DW_AT_name
        .byte   0x1     # DW_AT_decl_file
        .byte   0x10    # DW_AT_decl_line
        .long   0x285   # DW_AT_type
        .byte   0x5     # DW_AT_location
        .byte   0x3     # DW_OP_addr
        .long   _ZZN1AC1EiiE6foofoo

So this was fixed in 4.1.0 and above as 4.0.0 does not produce the location.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.1.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

[Bug debug/33044] Local variables in C++ constructor not visible for debugging

[seppo at totalviewtech dot com]

------- Comment #3 from seppo at totalviewtech dot com  2007-08-14 20:32 -------
Hi Andrew,

Thanks for the quick response. The static variable foofoo seems to be OK in
DWARF and the DW_AT_location is there. But for some reason I still do not see
the _non-static_ iii variable and its DW_AT_location attribute in DWARF. The
DWARF information is completely missing (at least with the 4.1.2 version).

Interestingly enough with 4.0.3 both iii and foofoo are listed, but both miss
the DW_AT_location attribute. With 4.1.2 the latter is fixed and the former has
been dropped altogether?

Thanks,
Seppo


-- 

seppo at totalviewtech dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|FIXED                       |
            Version|3.2.3                       |4.1.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

[Bug debug/33044] Local variables in C++ constructor not visible for debugging

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2007-08-14 22:40 -------
The iii bug is PR 27574.  
So one problem was fixed for 4.1.0 and the other problem is already recorded as
a different PR number so I am going to close this as fixed.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

[Bug debug/33044] Local variables in C++ constructor not visible for debugging

[nikolay at totalviewtech dot com]

------- Comment #5 from nikolay at totalviewtech dot com  2007-08-24 13:15 -------
This is not fixed neither in 4.1.0 nor in any later version. The problem is
that DIE for static foofoo was indeed produced, but produced in wrong place.
<2><260>: Abbrev Number: 7 (DW_TAG_subprogram)  --- Constructor declaration
     DW_AT_external    : 1      
     DW_AT_name        : A      
     DW_AT_decl_file   : 1      
     DW_AT_decl_line   : 16     
     DW_AT_declaration : 1      
<1><27f>: Abbrev Number: 10 (DW_TAG_subprogram) --- Broken declaration 
     DW_AT_sibling     : <2bc>  
     DW_AT_specification: <260> 
     DW_AT_decl_line   : 22     
     DW_AT_inline      : 0      (not inlined)
.....
 <2><2a7>: Abbrev Number: 13 (DW_TAG_variable)- this is where foofoo was emited
     DW_AT_name        : foofoo 
     DW_AT_decl_file   : 1      
     DW_AT_decl_line   : 28     
     DW_AT_type        : <3a1>  
     DW_AT_location    : 5 byte block: 3 c0 86 4 8      (DW_OP_addr: 80486c0)
<1><2c1>: Abbrev Number: 15 (DW_TAG_subprogram) -- real constructor declaration
     DW_AT_sibling     : <2fd>  
     DW_AT_abstract_origin: <27f>       
     DW_AT_low_pc      : 0x8048474      
     DW_AT_high_pc     : 0x80484ed      
     DW_AT_frame_base  : 0      (location list)
 <2><2ee>: Abbrev Number: 17 (DW_TAG_lexical_block) -- this is the scope, where
foo and all other variables should be defined. 
     DW_AT_low_pc      : 0x8048495      
     DW_AT_high_pc     : 0x80484eb      
 <3><2f7>: Abbrev Number: 18 (DW_TAG_variable)  --- this is supposed to be
"iii"
     DW_AT_location    : 2 byte block: 91 74    (DW_OP_fbreg: -12)
---------------------------------------------------------------------
So dwarf producer is clearly confused and emits static foofoo in wrong broken
subprogram declaration. Instead it should emit it inside lexical block <2ee> 


-- 

nikolay at totalviewtech dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nikolay at totalviewtech dot
                   |                            |com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

[Bug debug/33044] Local static variable in C++ constructor not visible for debugging

[seppo at totalviewtech dot com]

------- Comment #6 from seppo at totalviewtech dot com  2007-08-24 13:52 -------
Hi Andrew,

Reopened the bug (see comment above). Do also notice that the (due to the
above) static foofoo inside constructor is still not visible to either TV or
gdb. 

I have changed the title of the bug to reflect that we are only concerned of
static variable in this bug report (the gzz-bug #27574 covers the non-static
case).

Thanks,
Seppo


-- 

seppo at totalviewtech dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|FIXED                       |
            Summary|Local variables in C++      |Local static variable in C++
                   |constructor not visible for |constructor not visible for
                   |debugging                   |debugging


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

[Bug debug/33044] Local static variable in C++ constructor not visible for debugging

[pinskia at gcc dot gnu dot org]

------- Comment #7 from pinskia at gcc dot gnu dot org  2007-08-24 16:14 -------
This all comes down to cloning.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

[Bug debug/33044] Local static variable in C++ constructor not visible for debugging

[nikolay at totalviewtech dot com]

------- Comment #8 from nikolay at totalviewtech dot com  2007-08-24 16:45 -------
(In reply to comment #7)
> This all comes down to cloning.
> 

What do you mean?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

Re: [Bug debug/33044] Local static variable in C++ constructor not visible for debugging

[Andrew Pinski]

On 24 Aug 2007 16:45:41 -0000, nikolay at totalviewtech dot com
<gcc-bugzilla@gcc.gnu.org> wrote:
> What do you mean?

The IA64 C++ ABI requires two (or three) versions of constructor.  So
GCC "clones" functions to deal with that.  And we emit the context of
the local static variable part of the original function, not part of
any of its clones.

-- Pinski

[Bug debug/33044] Local static variable in C++ constructor not visible for debugging

[pinskia at gmail dot com]

------- Comment #9 from pinskia at gmail dot com  2007-08-24 16:51 -------
Subject: Re:  Local static variable in C++ constructor not visible for
debugging

On 24 Aug 2007 16:45:41 -0000, nikolay at totalviewtech dot com
<gcc-bugzilla@gcc.gnu.org> wrote:
> What do you mean?

The IA64 C++ ABI requires two (or three) versions of constructor.  So
GCC "clones" functions to deal with that.  And we emit the context of
the local static variable part of the original function, not part of
any of its clones.

-- Pinski


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

[Bug debug/33044] Local static variable in C++ constructor not visible for debugging

[rguenth at gcc dot gnu dot org]

------- Comment #10 from rguenth at gcc dot gnu dot org  2008-01-13 15:43 -------
Unclear status of this bug.  Removing target milestone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|4.1.0                       |---


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

[Bug debug/33044] Local static variable in C++ constructor not visible for debugging

[le dot ben dot smith at gmail dot com]

------- Comment #11 from le dot ben dot smith at gmail dot com  2008-08-27 23:26 -------
I just noticed this problem with gcc 4.3.0.  I'm not familiar with compiler
internals, so I don't understand all the details of the previous comments.  It
sounds like this is a gdb bug then...  Is that correct?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

[Bug debug/33044] Local static variable in C++ constructor not visible for debugging

[dodji at gcc dot gnu dot org]

------- Comment #12 from dodji at gcc dot gnu dot org  2008-08-29 09:58 -------
This is an update of what we get with gcc-4_3-branch.

For the program (line numbers added for better legibility):

     1  #include <stdio.h>
     2  class A {
     3  public:
     4    A (int a, int b);
     5    int a_;
     6    int b_;
     7    int c_;
     8  };
     9  
    10  A::A (int a, int b) : a_ (a), b_ (b), c_ (0)
    11  {
    12    int iii;
    13    iii = 42;
    14    c_ = a_ * b_;
    15    c_ += iii;
    16    static const int foofoo[6][4] = { {0,1,2,3},
    17                                      {1,2,3,4},
    18                                      {2,3,4,5},
    19                                      {3,4,5,6},
    20                                      {4,5,6,7},
    21                                      {5,6,7,8} };
    22  
    23    printf("c_ = %d\n", c_);
    24    printf("foofoo = %d\n", foofoo);
    25  }
    26  
    27  int main (int, char* *)
    28  {
    29    int a = 34, b = 56;
    30    A x (a, b);
    31    return x.a_ + x.b_;
    32  }
    33  

I get the dwarf info below:

[...]

<1><c5>: Abbrev Number: 11 (DW_TAG_subprogram) <-- //This is the A::A
constructor at line 10.
    <c6>   DW_AT_specification: <0xa6>  
    <ca>   DW_AT_decl_line   : 10       
    <cb>   DW_AT_inline      : 0        (not inlined)
    <cc>   DW_AT_sibling     : <0x102>  
 <2><d0>: Abbrev Number: 12 (DW_TAG_formal_parameter)
    <d1>   DW_AT_name        : (indirect string, offset: 0x47): this    
    <d5>   DW_AT_type        : <0x102>  
    <d9>   DW_AT_artificial  : 1        
 <2><da>: Abbrev Number: 13 (DW_TAG_formal_parameter)
    <db>   DW_AT_name        : a        
    <dd>   DW_AT_decl_file   : 1        
    <de>   DW_AT_decl_line   : 10       
    <df>   DW_AT_type        : <0x57>   
 <2><e3>: Abbrev Number: 13 (DW_TAG_formal_parameter)
    <e4>   DW_AT_name        : b        
    <e6>   DW_AT_decl_file   : 1        
    <e7>   DW_AT_decl_line   : 10       
    <e8>   DW_AT_type        : <0x57>   
 <2><ec>: Abbrev Number: 14 (DW_TAG_variable) <--- this if the foofoo variable
    <ed>   DW_AT_name        : (indirect string, offset: 0x0): foofoo
    <f1>   DW_AT_decl_file   : 1        
    <f2>   DW_AT_decl_line   : 16 
    <f3>   DW_AT_type        : <0x214>  
    <f7>   DW_AT_location    : 9 byte block: 3 20 8 40 0 0 0 0 0       
(DW_OP_addr: 400820)

[...]

So we see here that the foofoo variable is generated with an DW_AT_location,
inside the A::A constructor we are interested in.

However, in GDB, at line 23:
(gdb) bt
#0  A (this=0x7fff6616bd80, a=34, b=56) at test-PR33044.cc:23
#1  0x0000000000400645 in main () at test-PR33044.cc:30

I get:
(gdb) p foofoo
No symbol "foofoo" in current context.

As Andrew pointed, gcc can generate several copies (two, or three) of a given
constructor. Those copies don't necessarily have the same signatures, of
course. So A::A(int, int) might yield to an additional copy of the constructor
being generated.
The debugging for A::A(int, int) info is only generated for the "initial"
constructor. Not for the additional copy.

So my question now is what happens when GDB actually breaks in the additional
copy ? Can it detect that it broke in a constructor that is "only" a copy of
the "real" one ? Or does it expect that all the copies be associated with
debugging info ?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

[Bug debug/33044] Local static variable in C++ constructor not visible for debugging

[dodji at gcc dot gnu dot org]

------- Comment #13 from dodji at gcc dot gnu dot org  2008-08-29 14:41 -------
Created an attachment (id=16162)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=16162&action=view)
The debug info of the program

Okay, here is a more accurate analysis. I will refer to the debug info
attached.

As I said in my previous comment, the foofoo variable is decribed by DIE <ec>,
which is a child DIE of the DW_TAG_subprogram DIE at <c5>. <c5> is the DIE of
the constructor A::A(int, int).

In GDB, When I set a beakpoint in A::A(int, int) the debugger actually stops on
a subprogram which DIE is <107>. This <107> DIE describes an "Out-of-Line
Instance" of of A::A(int, int). So <107> rightfully has an
DW_AT_abstract_origin attribute that links back to the abstract tree of
A::A(int, int) at <c5>.

However, foofoo does not have any DIE that is a child node of <107>. The DIE
<14d> seems to be the DIE describing iii, not foofoo.
That might be the reason why GDB is not finding foofoo.

On the other hand, the DWARF3 specs says (in section 3.3.8.2, point 1).

"An entry in the concrete instance tree may be omitted if it contains only a
DW_AT_abstract_origin attribute and either has no children, or its children are
omitted. Such
entries would provide no useful information.".

This text is at PDF page 65 (or document page 53).

So by the DWARF3 spec, I would believe that the debugger should be able to walk
through the DIE of the abstract tree A::A(int, int) to find the entry <ec> that
describes foofoo.

On the other hand, GCC could maybe play nice and generate a DIE for foofoo as a
child node of the lexical block of <107>. But then maybe that would incur some
dwarf bloat.

Any comment ?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044

[Bug debug/33044] Local static variable in C++ constructor not visible for debugging

[jason at gcc dot gnu dot org]

------- Comment #14 from jason at gcc dot gnu dot org  2008-08-29 16:09 -------
Dodji is right: since the variable is shared between all concrete instances,
there is no need to repeat anything about it in the concrete instance.  The
debugger should find the information it wants in the abstract instance.

This is a bug in GDB.


-- 

jason at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33044