[Dwarf-Discuss] Question / Proposal: breakpoints at global C++ constructors and destructors

[Daniel Gutson]

On Sun, Oct 5, 2014 at 12:47 PM, Michael Eager <eager at eagercon.com> wrote:
> On 10/05/14 07:27, Daniel Gutson wrote:
>>
>> Hello,
>>
>>     this is my first post to this list.
>>
>> Context: I've been a gdb and gcc maintainer in the past, but I'm not a
>> DWARF expert, so my post is
>> from the user's POV.
>>
>> PROBLEM: ability to break in (all) the global objects' constructors
>> (that is, before main() is called),
>> and destructors (after main() ).
>>
>> As a matter of proof of concept, we've developed a gdb script that is
>> also nontrivial and imperfect.
>> FWIW, there were two ways: one implementation-agnostic by regex
>> finding the ctors of all objects and
>> adding breakpoints in all of them, then breaking at main, disabling
>> the former and continuing;
>> another way was implementation-specific, knowing the internals of the
>> __static_initialization_and_destruction_0
>> mechanism. Our proof of concept used the first approach but had a lot of
>> issues.
>>
>> So, it would be absolutely trivial if there was a DW_CTOR_CALL /
>> DW_DTOR_CALL with the address
>> of the call instruction, so the debugger can break on those calls, and
>> do a step-into to get into the ctor/dtor body.
>
>
> I don't think that a special DWARF TAG would be required for this.
> You could use DW_TAG_subprogram to describe the ctor/dtor routine,
> marked with with DW_AT_artificial.

It's not a solution, because the problem is not identifying the
function (the constructor
in this case), but the CALL to the constructor.
Why? Because the same class could have several global instances, and non-global
(attributes, local) instances.
So what is needed is to identify the invoking places.

>
>
> --
> Michael Eager    eager at eagercon.com
> 1960 Park Blvd., Palo Alto, CA 94306  650-325-8077



-- 

Daniel F. Gutson
Chief Engineering Officer, SPD


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