Re: [linuxsh-dev] init problems on MMU-less SH-4

[David M. <da...@sn...>]

Jivin Paul Mundt lays it down ...
> Hi,
> 
> Running into a bit of weirdness, and was curious if anyone had seen this
> before.
> 
> I'm presently running on an SH-4, with the MMU implicitly turned off
> (and CONFIG_MMU unset). I've taken care of dealing with paging_init()
> changes, tlb ops, etc. to deal with the lack of an MMU, and none of that
> appears to be an issue. 
> 
> My current problem is that the minute init tries to start, I get endless
> unaligned userspace access traps. If I implicitly flush the cache prior
> to turning the MMU off, I don't have this problem, instead it runs into
> a sort of livelock situation where init just hangs .. though I'm still
> able to ping the target. Flushing the tlb prior to turning the MMU off
> for added sanity doesn't seem to make a difference one way or the other.
> 
> Also, flushing the cache at context switch time (to work around
> potential aliasing issues, SH is VIPT) doesn't seem to make a difference
> here either. I haven't tried running uncached yet, though I doubt that's
> an issue here.
> 
> Anyone seen this kind of behavior before? Suggestions?

I suspect that you are still running ELF programs.  When you turn off the
MMU support in the kernel,  the rules for applications change a little.
They cannot be paged in for example, and they have to be loaded (and
relocated) at run time.  Normal elf programs are loaded at a fixed
addresses and this cannot work without an MMU.

The uClinux guys use a program called elf2flt (ELF to flat) to make flat
binaries that can be run without an MMU.  You can find it at:

	http://cvs.uclinux.org/cgi-bin/cvsweb/elf2flt/

I don't believe there is SH support in it at the moment,  but it isn't a
huge amount of work. Generally only a few relocation types need to be
handled,

Cheers,
Davidm

-- 
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