[rtems-users] C++ Virtual Functions

[Joel Sherrill <joel@OARcorp.com>]

Sergei Organov wrote:
> "Smith, Gene" <gene.smith at siemens.com> writes:
> 
> 
>>Sergei Organov wrote, On 2/2/2005 12:10 PM:
>>
>>
>>>"Smith, Gene" <Gene.Smith at siemens.com> writes:
>>>
>>
>>>>I am having some problems running code containing C++ virtual
>>>>functions in rtems. When the code tries to branch to a virtual
>>>>function address using "bctrl" instruction, the address (in ctr) is
>>>>way out of range and results in a machine check exception.
>>>>
>>>>Is there anything I need to do special in rtems for virtual functions to
>>>>work? Is anyone using virtual functions, pure or impure, in rtems? I am
>>>>still using rtems 4.6.1 and my ppc40x-derived bsp.
>>>
>>>Besides what others have already suggested to check for, it could be the
>>
>>>case that you call a virtual member function of a static or global
>>>object for which constructor hasn't been invoked (yet). In this case
>>>virtual table pointer in the object isn't initialized. Global
>>>constructors are invoked by special startup code so you need to check if
>>>this code is linked in and executed. Check for .ctors section in the
>>>executable as well.
>>
>>Yes, that is what I just concluded in my previous post to this thread.
>>I could see *no* .ctors or .dtors sections in my original output file.
>>The .ctors and .dtors sections were supposedly placed into the .text
>>section (see the attached linkcmds on previous msg). I then moved them
>>out of .text into their own sections following .got2 (as shown in
>>referenced example linkcmds, psim and motorola) and now I do see the
>>sections .c(d)tors in the output following .got2. However, I still
>>don't seem to see any initialization (construction) of the global
>>object in question (its constructor is never hit when a breakpoint is
>>put on it).
> 
> 
> The code that calls constructors doesn't in fact use .ctors section in
> any way, it uses __CTOR_LIST__  and probably __CTOR_END__ symbols that
> seem to be correctly defined by your linker script, so moving all that
> from .text to separate .ctors won't help.
> 
> Most probably you don't link in correct C++ startup code or somehow it's
> not called. There are guys on the list that know much better than me how
> C++ startup code is linked in and invoked in RTEMS. I can't tell out of
> my head as for historical reasons I do it manually in my projects, not
> using RTEMS standard ways. I.e., I have my own routine that calls all
> the functions put into the table referenced to by __CTOR_LIST__ and call
> it before main().
> 

psim in the CVS tree and head of the 4.6 branch works for C++ and 
exceptions.  The trick is in the linkcmds and bsp_specs.  If you get 
those right, it should just work.

bsp_specs
==========
The *startfile section needs to include ecrti, rtems_crti, and crtbegin.

The *endfile section needs to include crtend and ecrtn.

CHeck out psim/bsp_specs on the head of the 4.6 branch or the trunk.
It looks different from the gen405/bsp_specs.

linkcmds
=========
Look for the .init and .fini sections and the CTOR/DTOR (caps) related
sections.

--joel