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[英]Using the Haskell FFI to marshal structs; also, how to use FunPtr
[英]How do I use a FunPtr from Haskell?
假設有以下文件:
測試2.h:
typedef int (*signature) ();
extern const signature lol2;
測試2.c:
#include "test2.h"
int lol() {
return 42;
}
const signature lol2 = lol;
測試2.hs:
module Main where
import Foreign.C
import Foreign.Ptr
type Fun =
IO CInt
foreign import ccall
"test2.h lol2"
fun_ptr
:: FunPtr Fun
foreign import ccall "dynamic" mkFun :: FunPtr Fun -> Fun
lol = mkFun fun_ptr
main = do
fortytwo <- lol
putStrLn $ show $ fortytwo
使用以下編譯:
gcc -shared test2.c -Wall -Wextra -o libtest2.so -g3 -ggdb3
ghc -o test2 Test2.hs -ltest2 -optl-Wl,-rpath,. -L. -g
(GHC 在 lol2 聲明之前發出關於缺少“&”的警告,但我認為警告是錯誤的,所以我忽略它。另外,請注意我沒有使用-dynamic
。如果我這樣做,結果是一樣的)
但是,我在運行時得到一個 SIGSEGV:
(gdb) break scheduleWaitThread
Breakpoint 1 at 0x468150: file rts/Schedule.c, line 2509.
(gdb) r
Starting program: [...]/test2
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Breakpoint 1, scheduleWaitThread (tso=0x4200105388, ret=ret@entry=0x0, pcap=pcap@entry=0x7fffffffd7f8) at rts/Schedule.c:2509
2509 rts/Schedule.c: No such file or directory.
(gdb) bt
#0 scheduleWaitThread (tso=0x4200105388, ret=ret@entry=0x0, pcap=pcap@entry=0x7fffffffd7f8) at rts/Schedule.c:2509
#1 0x0000000000483864 in rts_evalLazyIO (cap=cap@entry=0x7fffffffd7f8, p=p@entry=0x4a5420, ret=ret@entry=0x0) at rts/RtsAPI.c:530
#2 0x00000000004707ae in hs_main (argc=1, argv=0x7fffffffd9e8, main_closure=0x4a5420, rts_config=...) at rts/RtsMain.c:72
#3 0x0000000000406b46 in main ()
(gdb) finish
Run till exit from #0 scheduleWaitThread (tso=0x4200105388, ret=ret@entry=0x0, pcap=pcap@entry=0x7fffffffd7f8) at rts/Schedule.c:2509
Program received signal SIGSEGV, Segmentation fault.
0x00000000004a4d90 in lol2 ()
(gdb)
崩潰后堆棧似乎無法使用:
(gdb) bt
#0 0x00000000004a4d90 in lol2 ()
#1 0x000000000040669d in r2ad_info ()
#2 0x0000000000000000 in ?? ()
我究竟做錯了什么? 我該如何調試?
ccall
只能導入函數,而lol2
是沒有函數的。 使用帶有value
限定的capi
導入:
{-# LANGUAGE CApiFFI #-}
module Main where
-- ... etc ...
foreign import capi "test2.h value lol2" fun_ptr :: FunPtr Fun
-- ... etc ...
這不是很明顯,但手冊說要這樣做,並且它有效。 您看到的警告信息仍然出現; 我認為您可能想將其報告為錯誤。
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