Forcing a linking error?

[Edward Z. Yang]

Omer, this ticket may be of interest to you:

    https://ghc.haskell.org/trac/ghc/ticket/7790

Edward

Excerpts from Ömer Sinan Ağacan's message of 2015-08-14 03:51:49 -0700:
> Here's an example that fails with a link time error when -threaded is not used:
> 
>     ➜  rts_test  ghc --make Main.hs
>     [1 of 1] Compiling Main             ( Main.hs, Main.o )
>     Linking Main ...
>     Main.o: In function `rn4_info':
>     (.text+0x26): undefined reference to `wakeUpRts'
>     collect2: error: ld returned 1 exit status
> 
> With -threaded it works:
> 
>     ➜  rts_test  ghc --make Main.hs -threaded
>     Linking Main ...
> 
> Code:
> 
>     ➜  rts_test  cat Main.hs
>     {-# LANGUAGE ForeignFunctionInterface #-}
> 
>     module Main where
> 
>     foreign import ccall "wakeUpRts" wakeUpRts :: IO ()
> 
>     main :: IO ()
>     main = return ()
> 
> What I did is basically I found a function in GHC RTS that is only defined when
> THREADED_RTS is defined and referred to it in my program.
> 
> 2015-08-14 3:59 GMT-04:00 Erik de Castro Lopo <mle+hs at mega-nerd.com>:
> > Dear ghc-devs,
> >
> > There is a commonly used library which has at least one function
> > that when compiled into a program, requires the threaded run time
> > system. Without the threaded runtime, the program just hangs.
> >
> > One kludgy solution to this problem is to have the function check
> > for Control.Concurrent.rtsSupportsBoundThreads being true and
> > throwing an error if its not. However, it would be much nicer if
> > this could be turned into a link time error.
> >
> > Anyone have any ideas how this might be done?
> >
> > Cheers,
> > Eri
> > --
> > ----------------------------------------------------------------------
> > Erik de Castro Lopo
> > http://www.mega-nerd.com/
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