[GSOC2013] Dynamic object file loading

Chris Johns chrisj at rtems.org
Sat Apr 20 04:01:58 UTC 2013

Peng Fan wrote:
>     Added the code, I can see the three files: libx.a shell-init  x.rap
>     Here appears another problem:
>     When"rap ld ./x.rap", it tells"error: loading: (0)"
>     When"dlo x.rap","error: duplicate global symbol: hello". However,  dlo libx.a:xa.c.1.o and dlo libx.a:x-long-name-to-create-gnu-extension-in-archive.c.1.o is ok.
> Tried to find why "When "rap ld ./x.rap", it tells "error: loading: (0)""

Did you grep for the string and set a break point in it and then look at 
the back trace ? This is a pretty bad error message. Something is wrong 

> I trace rtld using sparc-rtems4.11-gdb.
> In rap.c, there are two functions to do the loading ,linking and finding
> symbol job, dlopen foucsing on loading and resolving symbols, while
> dlsym returns the symbol address.


> When debugging dlopen returns sucessfully, but "init = dlsym
> (app->handle, "*rtems*");" returns with "init=NULL".Thus rap load failed.

What is "*rtems*" ? Wild cards will not work.

> In dlsym, It first try find the symbol in it's local "global_table".


> In
> x.rap, It's global_table includes "hello", "w_writeln" ,"x_writeln",
> "y_writeln", "z_writeln", "public", "my_main". with no one matches
> "*rtems*". Then It tries to find the symbol in global symbol which maybe
> generated in rtld-gsyms.c using a hash method.However, it still can not
> find the    match "rtems" symbol. Thus, failed.

Oh ok I get what is happening, yes this is correct. The symbols is 
'rtems' and it is a kind of 'main' for the RTEMS application. It is 
nothing more than that. The x.rap is a progression and I ended up 
testing the whole think with a waf based libbsdports that create a RAP 
image. I need to get this out onto a server somewhere.

> I do not know the "rtems" symbol means what. I see it is assigned to
> init, and then init(*, *). I am confusing  about why "rtems".

This is understandable because I failed to add the reason to the doco. 
As I said this is an RTEMS Application's main. I did not want to use 
main because this has a well known and understood use.

Well done on getting this far. If you add an 'rtems' function to the 
x.rap and have it print something the load should work.


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