[rtems-users] C++ Virtual Functions

[Sergei Organov]

"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().

-- 
Sergei.