GHCi不适用于FFI导出声明/共享库

Question

关于Haskell中的FFI和GHC的交互模式我有一个问题.

(来源也可以通过要点获得):

FFISo.hs:

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ForeignFunctionInterface #-}
module Main where

import qualified Data.ByteString.Char8 as B

foreign import ccall "callMeFromHaskell"
  callMeFromHaskell :: IO ()

foreign export ccall callMeFromC :: IO ()
callMeFromC :: IO ()
callMeFromC = B.putStrLn "callMeFromC"

main :: IO ()
main = do
  B.putStrLn "main"
  callMeFromHaskell
  return ()

抄送:

#include <stdio.h>

void callMeFromC(void);

void callMeFromHaskell(void)
{   
    printf("callMeFromHaskell\n");
    callMeFromC();
}

Makefile文件:

GHC_OPT := -Wall -O2 -fno-warn-unused-do-bind

all: ffiso

test: ffiso
    ./$<

ffiso: FFISo.hs c.c
    ghc --make $(GHC_OPT) $^ -o $@

clean:
    rm -rf *.hi *.o ffiso *_stub.*

ghci0: ffiso
    echo main | ghci FFISo.hs

ghci1: ffiso
    echo main | ghci FFISo.hs c.o

ghci2: ffiso
    echo main | ghci FFISo.hs c.o FFISo.o

编译和链接工作正常:

$ make test
ghc --make -Wall -O2 -fno-warn-unused-do-bind FFISo.hs c.c -o ffiso
[1 of 1] Compiling Main             ( FFISo.hs, FFISo.o )
Linking ffiso ...
./ffiso
main
callMeFromHaskell
callMeFromC

但是,如果我想使用GHCi,则会失败并显示以下消息:

$ make ghci0
echo main | ghci FFISo.hs
GHCi, version 7.4.1: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Ok, modules loaded: Main.
Prelude Main> Loading package bytestring-0.9.2.1 ... linking ... done.
<interactive>: FFISo.o: unknown symbol `callMeFromHaskell'

Prelude Main> Leaving GHCi.

好吧,让我们尝试给GHCi提供c.o目标文件.

$ make ghci1
echo main | ghci FFISo.hs c.o
GHCi, version 7.4.1: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading object (static) c.o ... done
ghc: c.o: unknown symbol `callMeFromC'
linking extra libraries/objects failed
make: *** [ghci1] Error 1
final link ... 

哦好吧......让我们试试FFISo.o:

$ make ghci2
echo main | ghci FFISo.hs c.o FFISo.o
GHCi, version 7.4.1: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading object (static) c.o ... done
Loading object (static) FFISo.o ... done
ghc: FFISo.o: unknown symbol `bytestringzm0zi9zi2zi1_DataziByteStringziInternal_PS_con_info'
linking extra libraries/objects failed
make: *** [ghci2] Error 1
final link ... 

那就是我被困住的地方.

我用两个不同的环境测试了它,结果相同:

$ # system 1
$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.4.1
$ uname -a
Linux phenom 3.2.13-1-ARCH #1 SMP PREEMPT Sat Mar 24 09:10:39 CET 2012 x86_64 AMD Phenom(tm) II X6 1055T Processor AuthenticAMD GNU/Linux

$ # system 2
$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.12.1
$ uname -a
Linux hermann 2.6.32-22-generic-pae #36-Ubuntu SMP Thu Jun 3 23:14:23 UTC 2010 i686 GNU/Linux

Answer 1

在调用GHCi时,您需要指定一些要链接的对象,因为在c.o链接顺序时C对象特别挑剔.

首先,您需要添加bytestring包的目标文件.这是通过添加-package bytestring到GHCi命令行来完成的.

然后,您需要添加定义的实际对象文件callMeFromC.当FFISo.hs被编译,它不会产生一个输出的目标文件callMeFromC.它改为使用GHC命名约定和导出Main_zdfcallMeFromCzuak4_closure,它实际上是一个静态全局变量,指向包含实际函数定义和环境的闭包/"thunk".这样你就不能这样写:

foregin export ccall foo :: IO ()
foo = undefined

...并且一旦程序启动就会使运行时崩溃,因为foo无法评估"函数值" .只有在实际使用该功能后才会检查功能定义.

GHC生成一个存根文件,其中包含用于从C调用Haskell函数的C代码.此文件被调用FFISo_stub.c,并FFISo_stub.o为您编译.该目标文件导出callMeFromC可以直接调用的"C版本" .随意检查生成的代码,这很有意思.

总而言之,在调用GHCi时需要使用此命令行:

ghci -package bytestring FFISo.o c.o FFISo_stub.o FFISo.hs