lnkscript .ctors/.dtors; Must be in RAM or can be in ROM?

[William A. Gatliff]

Jeff:


.ctor and .dtor are function pointer tables.

To see how they work, compile any C++ module that has global object
instantiations in it, and look at the assembly language.  In general,
what happens is (at least for the PPC EABI target) the compiler
generates a function that contains a "this" pointer for the global
object, and a call to the object's constructor.

.ctor and .dtor are lists of pointers to these functions.  For the
EABI target, putting them in ROM is ok.

Here's a snipped from some of my ppc-eabi startup code, that you may
find illustrative:


/* a symbol created by the linker, resides at the start of .ctor. */
extern void (*__CTOR_LIST__[])(void);

/* the end of .ctor */
extern void (*__CTOR_END__[])(void);

/*
  Invokes constructors by walking through
  all the function pointers in the .ctor section.
*/
void __eabi_ctors ( void )
{
  int wctor;
  int nctor = __CTOR_END__ - __CTOR_LIST__;
 
 
  for( wctor = 0; wctor < nctor; wctor++ )
    (*(__CTOR_LIST__[wctor]))();
 
  return;
}


HTH,

b.g.

On Mon, Jul 30, 2001 at 06:13:17PM -0500, Jeff Frohwein wrote:
>  A friend of mine has a link script which includes the following sections
> for embedded c++ support. I have spent the last 8 hours searching these
> archives & doing web searches to figure out if it is reasonable to put
> these sections in ROM.
> 
>  I have found several posts that mention they should be in RAM. However,
> they did not state their reasoning for this.
> 
>  My friend suggests that he has had no problems with his code by putting
> then in ROM.
> 
>  Can anyone guide me towards a definitive answer or direct me to where I
> can locate such?
> 
>  Thanks,
> 
>  Jeff
> ---------------
> .ctors   :
>   {
>     KEEP (*crtbegin.o(.ctors))
>     KEEP (*(EXCLUDE_FILE (*crtend.o) .ctors))
>     KEEP (*(SORT(.ctors.*)))
>     KEEP (*(.ctors))
>     . = ALIGN(4);
>   } >ROM =0
> 
>   .dtors   :
>   {
>     KEEP (*crtbegin.o(.dtors))
> 
>     KEEP (*(EXCLUDE_FILE (*crtend.o) .dtors))
>     KEEP (*(SORT(.dtors.*)))
>     KEEP (*(.dtors))
>     . = ALIGN(4);
>   } >ROM =0
> 
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-- 
Bill Gatliff
bgat@billgatliff.com

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