[okl4-developer] FASS on gumstix

[Jamie Lennox]

Jamie Lennox wrote:
> 
> Hi all,
> 
> Having been stumped over benchmarks in a FASS system and looking into 
> the way that FASS/FCSE works then the default configurations for gumstix 
> aren't correct to enable FASS. Predominately binaries should be linked 
> within the 0x0-0x1FFFFFFF range. How do we go about enabling FASS for 
> iguana (OKL4 v2.1.1 - patch 9) when all protection domains are linked 
> into the same address space and binary? Where is this being implemented? 
> as from what i can see it appears that the kernel is emulating fass 
> rather than using it.
> 
> Thanks,
> Jamie
> 
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> 

I realise the initial post of this was a little ambiguous, so i'll let you
know what i've discovered. On a gumstix when sending an IPC the first thing
that happens on the return from a call is the application will fault on its
stack pointer address. Looking through everything the stack is allocated to
the application by elfweaver/build system and has been allocated within the
range of address space provided to iguana root server. 

I think that this crossing of fass boundaries has marked the PDs as dirty
and then the TLB is flushed, then on return from the next context switch we
have to reload the stack pointer. 

So my questions are i suppose: 
- Does this sound correct? Why else would it fault on the stack after every
return from a syscall (that involved a context switch)?
- How do i force the build system to locate the stack and all other sections
into the same slice of 32 MB memory so FASS will work?
- The ARMv5 default vaddress is 0x80000000 and v4 is 0x10000, my reading of
FCSE says that everything should be linked into 0x00000000-0x01FFFFFFFF. Is
OKL4 doing this as a translation or does arm simply truncate this when a pid
is written?

If it appears i have the wrong impression of FASS then please feel free to
straighten it out also 

Thanks Jamie


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