Haskell on risc os!

Hello!

Thought I’d mention that I have just finished building the JHC as a cross compiler to risc os!
GHC is a much harder code base to port, but I have made progress in that area too, although it may come down to waiting for GCCSDK to update their gcc version.

If you want to have a play, you can find a docker image here

Brilliant!

I had to work out how to use docker first, here’s what I did

1. Install docker using package manager
2. Make file ~/Main.hs with

main :: IO ()
main = putStrLn "Hello, world!"

3.

sudo -aG docker myusername
(restart)
sudo systemctl start docker
docker pull yobson/riscos-gccsdk-jhc
docker images
(look at id for image)
docker run -it <id for image>
docker ps
(look at container name)
docker cp ~/Main.hs containername:/root/Main.hs

Now in container

# arm-unknown-riscos-jhc Main.hs

Back on host

docker cp containername:/root/hs,e1f ~/hs,e1f

4. Then copied hs,e1f to risc os and ran it.

I wonder how _swix would look? Maybe

import Data.Word
data Arg = String s | Word8 b | Word32 w | Int i | Bool b
swix :: String -> [Int] -> [Int] -> [Arg] -> IO [Word32]
swix name in_regs out_regs in_args = out_words

so

main = do
  swix "OS_Write0" [0] [] [String "Hello"]
  swix "OS_NewLine" [] [] []
  rs <- swix "OS_ReadModeVariable" [0,1] [2] [-1, 4]
  putStrLn $ "XEigFactor:" ++ show (head rs)

Where should I go in the docker container to see the risc os changes you’ve made to jhc?

So far, other than getting it to build the rts correctly for risc os, I’ve done nothing!

The plan is risc os libraries next. I’m thinking toolbox or oslib first.

If you want to make a base risc os library, I’d be happy to include it in the container

Which version of gcc do you use? There are new versions in the autobuilder directory.

I’m quite liking jhc.

I think what ghc would help with is errors. I’d expect when a SWI generates an error for an exception to be raised in Haskell. So then you could go

import Control.Exception
import OSLib.OS

myError :: Error
myError = Error {errnum = 3, errmess = "An error"}

main :: IO ()
main = catch (os_generate_error myError)
             (\Error {errnum = n, errmess = m} ->
               putStrLn $ "SWI generated error:" ++ m)

But catch doesn’t work in jhc.

Unfortunately jhc’s garbage collector is picking up a null pointer. Specifically the argument val of s_set_used_bit called by gc_add_grey called by gc_perform_gc.

I don’t know how to fix this :-(

Great news James – thanks for working on this!

Julie! Feel free to provide some code for me to look at. I’ve hacked on this compiler a lot in the past!

And Michael, is that a gcc cross compiler? Or Risc os compiler? I need a cross compiler and posix libraries in order to bootstrap GHC.

Feel free to provide some code for me to look at.

Since then I’ve found it’s making an array with a length of zero that causes a null-pointer to get fed into the garbage collector.

The code

import Data.Array
import System.Mem

main :: IO ()
main = do
  print $ (array (0, -1) [] :: Array Int Int)
  performGC

compiled with

jhc Main.hs -o Main -pjhc-1.0

prints

array (0,-1) []
Segmentation fault (core dumped)

Looking at the C it produces (-C —tdir=./), there’s a line

sptr_t* x418 = gc_array_alloc(gc,v163333528);

That function in gc_jhc.c is

// Allocate an array of count garbage collectable locations in the garbage
// collected heap.
heap_t A_STD
gc_array_alloc(gc_t gc, unsigned count)
{
        if (!count)
                return NULL;
        if (count <= GC_STATIC_ARRAY_NUM)
                return (wptr_t)s_alloc(gc, array_caches[count - 1]);
        if (count < GC_MAX_BLOCK_ENTRIES)
                return s_alloc(gc, find_cache(NULL, arena, count, count));
        return s_monoblock(arena, count, count, 0);
        abort();
}

In my example count is zero and the NULL sptr_t returned is put on the gc stack.

Maybe it should return TO_SPTR(P_VALUE, NULL) instead so that gc_peform_gc skips over the entry in the stack?