Dynamic load real-time tasks

[Chris Johns]

On 26/06/2017 18:34, Павел Жданов wrote:
> Hello everyone.
> 
> I'm interested in dynamic loading and have the following situation:
> 
>  1. There are two files init.c and dl.c.
>  2. dl.с defines rtems_main function . This function just print some string
>     using printf fuction. It complied to dl.o but not linked against standard
>     libraries so printf symbol is unresolved.
>  3. I want to load dl.o from init.с and use rtems_main function (with dl_open
>     and so on). Final init.exe is linked against standard libraries so it has
>     printf symbol resolved.
>  4. dl.o is loaded from the dos partition.
>  5. At the moment a can load dl.o and call rtems_main only if it doesn't use
>     printf or functions from other libraries.
> 
> My questions are:
> 
>  1. Is this scenario possible?

Yes.

>  2. How to link dl.o with init.exe to resolve printf (and may be other functions
>     that are used by rtems_main and resolved in init.exe)?

Have you loaded a symbol table for the base image that contains the 'printf'
function. To create see:

https://docs.rtems.org/branches/master/user/tools/index.html#rtems-symbols

> 
> Platfrom: i386, pc486. I tried to use rtems-ld and i386-rtems4.11-ld but could
> not resolve necessary symbols.
> 

Dynamic loading of code requires the dependence between your base image code,
dynamically loaded and the system libraries needs to be managed. You can do this
manually and Joel gave a hint, or could take a look at the RAP format executable
format the 'rtems-ld' generates.

Chris