cvs commit: fptools/ghc/docs/comm/the-beast driver.html
Manuel M. T. Chakravarty
Fri, 24 Aug 2001 15:56:32 +1000
"Simon Marlow" <firstname.lastname@example.org> wrote,
> > > This does, however, lead to a complication. Normal
> > > Haskell programs do not have a main function, so this is
> > > supplied by the RTS. It calls startupHaskell, which
> > > itself calls __init_PrelMain, which is therefore, since
> > > it occurs in the standard library, one of the symbols
> > > passed to the linker. However, when the main function is
> > > provided by the programmer (e.g. when there is no main
> > > module, but a C module instead), __init_PrelMain had
> > > better not be linked in, because it tries to call
> > > __init_Main, which won't exist.
> > >
> > > This reads to me as if the complication arises only because
> > > of the business of breaking the cycle between the RTS and
> > > HSstd. However, I think, this is not true. The RTS has to
> > > be linked in anyway. So, it will include a `main()', which
> > > overall leads to `__init_Main' being linked in (with or
> > > without cycle).
> > >
> > > Have I misunderstood you or do I misunderstand the setup
> > > itself?
> > Well, there's extra complication owing to the -u's, but
> > basically I think
> > you're right. The main() stuff leads to even more complications under
> > DLLized systems on Windows, after all. Perhaps I should write
> > something
> > about that too...
> The RTS's main() refers to __init_PrelMain which in turn refers to
> __init_Main. Although the RTS's main() might not be linked in if the
> program provides its own, the driver will normally force __init_PrelMain
> to be linked in anyway, using -u, because it's a back-reference from the
> RTS to HSstd. The -no-hs-main flag causes the driver not to do this.
So, the driver arranges that the C program providing the
main() that we want to use appears in the link line after
the RTS. Therefore, the RTS's main is never used and
without the -u the label __init_PrelMain wouldn't be
linked. Ok, got it.
I'll edit the explanation in the commentary a bit to make