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Dynamic Object File Loading



Chris Johns wrote:
> Till Straumann wrote:
>> Chris Johns wrote:
>>> Bassem Fahmy wrote:
>>>  
>>>> Hi,
>>>> i'd like to handle the Dynamic Object File Loading. what shuold i 
>>>> do to start. is there in approvals i should take before i start.
>>>>  
>>>>     
>>>
>>> Please head to http://www.rtems.org/wiki/index.php/RTEMSSummerOfCode 
>>> in the wiki and the Student information sections.
>>>
>>> For dynamic loading there is a wiki page about the project:
>>>
>>>   http://www.rtems.org/wiki/index.php/Dynamic_Object_File_Loading
>>>
>>> If you have specific questions feel free to contact me.
>>>
>>>   
>> One thing the wiki doesn't mention (I know, I should add this 
>> myself...):
>>
>> Ordinary shared libraries (as created e.g., by the gnu tools) are
>> designed to be shared among processes where each process
>> possibly has a different virtual address map. Thus, the 
>> relocation-mechanism
>> has to be flexible enough to allow 'per-process' relocations.
>>
>> This is solved with a level of indirection (GOT and PLTs) which
>> add some overhead to every access of an external reference
>> (compared to static linking).
>>
>> Since RTEMS is a 'single-address-space' system there
>> is really no need for this indirection.
>>
>> Avoiding this overhead was one reason for implementing
>> cexp's linker as a static linker.
>>
>
> This is an important point and should be added to the Wiki. It is 
> important we capture things like this. I would add it but I feel I 
> would not do as good a job of it.
>
> Did you profile this or was it by inspection and analysis ?
The latter.
>
>> Also: the soon to be released, new version of cexp comes
>> with an ELF reader that may be useful to this project, too
>> (I was unable to find an ELF reader under a suitable
>> license which would not read the entire ELF file into
>> memory before operating on it. My ELF reader [on
>> a 'seekable' filesystem] only reads the required/requested
>> pieces of a file).
>
> Great and yes I also have not seen an ELF reader like this. Thanks.
>
> Regards
> Chris
>
>>
>> -- Till
>>
>>> Regards
>>> Chris
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>>>   
>>