Specifying Segment Attributes

Specifying Segment Attributes

[Prasad Venkata Boddupalli]

Hello,

I am writing a loader for a multi-threaded processor in which multiple
instances of an application run on different threads. Multiple
instances, besides their data segments mapped to a different physical
location also have a shared memory. The loader needs to recognize this
shared segment in the elf-executable. From the elf specification and the
linker script command language, I realized that one of the ways of
specifying the segment attribute as 'shared' is to use the 'PHDRS' command
and specify the attribute as part of the 'flags' of that segment.

Is there any other way as the use of PHDRS command will force one to
describe all segments ?

thanks,
Prasad.

Re: Specifying Segment Attributes

[Daniel Jacobowitz]

On Mon, Aug 29, 2005 at 12:25:22PM -0700, Prasad Venkata Boddupalli wrote:
> Hello,
> 
> I am writing a loader for a multi-threaded processor in which multiple
> instances of an application run on different threads. Multiple
> instances, besides their data segments mapped to a different physical
> location also have a shared memory. The loader needs to recognize this
> shared segment in the elf-executable. From the elf specification and the
> linker script command language, I realized that one of the ways of
> specifying the segment attribute as 'shared' is to use the 'PHDRS' command
> and specify the attribute as part of the 'flags' of that segment.
> 
> Is there any other way as the use of PHDRS command will force one to
> describe all segments ?

Not without changing the linker.

From something I sent to Ian last week, off list, so increment the
"third":

> This is the third time in the last couple of weeks that I've felt we                                  
> needed a mechanism to add an additional program header explicitly:                                    
> give it a name, add one to the number estimated by SIZEOF_HEADERS,                                    
> allow sections to be assigned to it... do you think it could be                                       
> feasibly implemented?  I haven't looked at the magic behind                                           
> SIZEOF_HEADERS.                                                                                       
>                                                                                                       
> But making folks define PHDRS manually when they really just want to                                  
> extend it is a real nuisance.                                                                         

Ian made some other suggestions, that I'll let him share if he wants
to, but I'm still attached to mine :-)

-- 
Daniel Jacobowitz
CodeSourcery, LLC

Re: Specifying Segment Attributes

[Nick Clifton]

Hi Prasad,

> location also have a shared memory. The loader needs to recognize this
> shared segment in the elf-executable. From the elf specification and the
> linker script command language, I realized that one of the ways of
> specifying the segment attribute as 'shared' is to use the 'PHDRS' command
> and specify the attribute as part of the 'flags' of that segment.
> 
> Is there any other way as the use of PHDRS command will force one to
> describe all segments ?

How about using memory regions ?  If you decide that the shared memory 
will always start at a specific, high address you could create a MEMORY 
region to describe this, and then assign any sections in the input files 
that need to go into shared memory to this region.

Cheers
   Nick