Re: trying to get a registerised alpha build

Duncan Coutts wrote:
> On Fri, 2006-03-31 at 11:43 +0100, Simon Marlow wrote:
>
> > Duncan Coutts wrote:
> >
> >
> > > What would you recommend is the bat way for us to verify that each bit
> > > of the registerised build is working? If we turn everything on including
> > > the mangler and it breaks where do we start debugging?
> >
> > I usually do this in one big step.
>
>
> Right 'o. :-)
>
>
> > Regarding debugging, I just wrote this wiki page:
> >
> >   http://hackage.haskell.org/trac/ghc/wiki/DebuggingGhcCrashes
> >
> > That should tell you everything you need to know, please feel free to 
> > expand it as you discover things.
>
>
> That's fantastic, thanks.
>
>
> > > Is it possible to build without tailcalls (ie using the
> > > mini-interpreter) but using the stg->machine register mappings?
> >
> > Certainly.  I think if you use -optc-DUSE_MINIINTERPRETER and 
> > -fno-asm-mangling everywhere, that should get you registers but no 
> > mangling or tail calls.
>
>
> Unfortunately this doesn't quite work because the TABLES_NEXT_TO_CODE
> ends up inconsistent. I'm not quite sure why that happens to be honest.
>
> Our clue is that the sanity check in initStorage barfs:
>   ASSERT(LOOKS_LIKE_CLOSURE_PTR(&stg_dummy_ret_closure));
>
> By looking at this in gdb (thanks again for the ghc gdb guide!) we found
> that this is because this closure was generated assuming
> TABLES_NEXT_TO_CODE to be true but of course since we're using
> -optc-DUSE_MINIINTERPRETER then the rts .c code is getting compiled
> with !TABLES_NEXT_TO_CODE which changes the definition of
> LOOKS_LIKE_CLOSURE_PTR.

I think the culprit is this bit of code in ghc/codeGen/SMRep.lhs:

tablesNextToCode :: Bool
#if defined(ia64_TARGET_ARCH) || defined(powerpc64_TARGET_ARCH)
tablesNextToCode = False
#else
tablesNextToCode = not opt_Unregisterised
#endif

This is the compiler's idea of TABLES_NEXT_TO_CODE, which doesn't match 
the RTS's idea from RtsConfig.h.  I suggest you just tweak this directly 
- the right way is probably to have another build system variable eg. 
$(GhcTablesNextToCode), but that's tricky to get right, and not 
generally useful (but by all means go ahead if you want).

Also, I'm worried about the generation of 
ghc/includes/DerivedConstants.h, because this code in 
ghc/includes/Makefile says this:

ifeq "$(GhcUnregisterised)" "YES"
SRC_CC_OPTS += -DNO_REGS -DUSE_MINIINTERPRETER
endif

So if you want USE_MINIINTERPRETER without GhcUnregisterised, it better 
be in SRC_CC_OPTS here.

Cheers,
        Simon