[Pkg-haskell-maintainers] Bug#722248: Bug#722248: ghci not provided on arm

[Thomas Preud'homme]

Le mardi 10 septembre 2013 18:23:42 Colin Watson a écrit :
> 
> Thanks for looking into this further.
> 
> I think that inlining the cache flush will mean that every chunk of
> bytecode assembled by the interpreter will flush the instruction cache
> every time it's called.  It will be even slower than it's necessary for
> it to be.  That in itself would probably be tolerable.
> 
> Much more importantly, though, this patch misses the point of flushing
> the instruction cache.  The point is that we need to flush the cache in
> order for the processor to reliably read back the code that we just
> wrote out; flushing the cache in that very code is not a viable approach
> to that, because the cache-flushing code itself might not be read.  So
> I'm afraid I don't think this is going to work properly.  It might work
> some of the time, of course, depending on cache locality, but I can't
> see how it would work reliably.

My apologize, I didn't realize this was the generated code. I don't know if 
it's because of the language but I can't make much sense of what the code is 
doing. I assumed this code was some jit compiler and that the jump was 
executed when a function has just been compiled in order to actually call that 
function. If it's part of the generated function indeed it's very suboptimal 
and won't work as you very well explained.

My apologize but I don't think I can bring this further without investing 
quite some time to understand the code.

> 
> I would suggest testing whether some reasonable stack actually builds
> with this; I don't know how much testing you did but it e.g. isn't
> enough to just start ghci.  Perhaps see if haskell-conduit runs its
> doctests successfully during build.

You're right, I should have done so. I don't know anything about ghc and I 
didn't know how to test it. I should have searched a bit on google, probably I 
would have found some code sample easily but I guess I lacked motivation.

Thanks for being so quick in looking at the patch.

Best regards,

Thomas
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