Question

我对Haskell中的FFI和GHC again的交互模式有疑问。

考虑FFISo.hs：

{-# LANGUAGE OverloadedStrings #-}
module Main where

import qualified Data.ByteString.Char8 as B

import FFIFun.Foo

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

c.c：

#include <stdio.h>

void callMeFromC(void);

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

FFIFun/Foo.hs：

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ForeignFunctionInterface #-}
module FFIFun.Foo 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"

和Makefile：

SHELL := bash

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,_stub.*} ffiso FFIFun/*{.hi,.o,_stub.*}

ghci: ffiso
    ghci -package bytestring FFIFun/Foo.o c.o FFISo.hs

你也发现它here as a gist。

所以，我现在的问题是：

$ make ghci
[...]
Ok, modules loaded: Main, FFIFun.Foo.
Prelude Main> -- fine, it's loading.
Prelude Main> :t callMeFromC

<interactive>:1:1: Not in scope: `callMeFromC'
Prelude Main> -- uhm, why?
Prelude Main> :t main
main :: IO ()
Prelude Main> main


GHCi runtime linker: fatal error: I found a duplicate definition for symbol
   FFIFunziFoo_callMeFromC_info
whilst processing object file
   ./FFIFun/Foo.o
This could be caused by:
   * Loading two different object files which export the same symbol
   * Specifying the same object file twice on the GHCi command line
   * An incorrect `package.conf' entry, causing some object to be
     loaded twice.
GHCi cannot safely continue in this situation.  Exiting now.  Sorry.

Hrmpf，这里有什么问题？有趣的是，我在i686上得到了一个不同的错误（上面，它是x86_64系统，但GHC 7.4.1）：

GHCi runtime linker: fatal error: I found a duplicate definition for symbol
   __stginit_FFIFunziFoo
whilst processing object file
   ./FFIFun/Foo.o
This could be caused by:
   * Loading two different object files which export the same symbol
   * Specifying the same object file twice on the GHCi command line
   * An incorrect `package.conf' entry, causing some object to be
     loaded twice.
GHCi cannot safely continue in this situation.  Exiting now.  Sorry.

此外，是否有一些关于它的文件？我觉得我是唯一一个在FFI和GHCi遇到困难的人。

编辑：请注意，make test工作正常：

$ ghc --make -Wall -O2 -fno-warn-unused-do-bind FFISo.hs c.c -o ffiso
[1 of 2] Compiling FFIFun.Foo       ( FFIFun/Foo.hs, FFIFun/Foo.o )
[2 of 2] Compiling Main             ( FFISo.hs, FFISo.o )
Linking ffiso ...
./ffiso
main
callMeFromC
callMeFromHaskell
callMeFromC

Answer 1

这是字节码解释器GHCi中动态链接目标文件的a known limitation。

如果加载静态链接到给定C对象的已编译代码，然后同时解释一些Haskell，它也通过FFI引用到同一个C对象，则运行时链接程序将被强制加载C对象动态。

现在您的地址空间中有两个版本的C符号，随后出现故障。

您必须在GHCi模式下解释所有内容，或者放弃使用GHCi进行此过程。对于某些OS链接器，您可以通过动态表（-x标志）公开静态链接的符号表。

使用FFI声明时GHCi运行时链接程序问题

1 个答案: