feasibility of modifying Linux ld-linux.so to identify which mapped files are shared libraries

[Ray Bryant]

Ian Wienand wrote:
> On Wed, May 11, 2005 at 09:33:34AM -0500, Ray Bryant wrote:
> 
>>Christoph Hellwig has suggested that instead we modify the dynamic loader
>>to mark mapped files in kernel memory as being shared libraries; this would
>>likely be communicated to the kernel via a new MMAP flag.
> 
> 
> I can see situations where this could be useful for more than just
> your immediate project.
> 
> We've demonstrated using IA64 protection keys for sharing TLB entries.
> If we knew at mmap() time this was a shared library we could setup
> keys then.  I think that could work out better than doing it carte
> blanche on MAP_SHARED since it might help manage the limited
> protection key registers better.
> 
> It might also act as an extra hint that this is a good candidate for a
> higher order superpage than it may otherwise be allocated.
> 
> Not that anyone cares what I think, but I can see how this could be
> useful.
> 
> -i
> ianw@gelato.unsw.edu.au
> http://www.gelato.unsw.edu.au

Hi Ian,

What kind of interface do you have in mind here?  I was thinking along the
lines of using a program to set some special bits (or add a special section)
to the elf header indicating that a corresponding bit needed to be passed into
mmap/madvise when the segment was mapped into memory by the dynamic loader.

Can you fit into such a scheme or do you need a more general capability?
(It sounds as if you might want to execute an arbitrary function at ld.so
time for each ELF segment, but that goes a bit beyond the scope of what I
was thinking.)

-- 
Best Regards,
Ray
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                   Ray Bryant
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