why adding extern(C) cause a runtime error?

[Dav1d via Digitalmars-d-learn]

On Saturday, 11 July 2015 at 01:22:14 UTC, mzfhhhh wrote:
> win7   x86  dmd2.067.1 ok
> ubuntu x64  dmd2.067.1 error
> -------------------------------------
> import std.stdio;
> import std.socket;
>
> extern(C)
> void recv()
> {
>     writeln("recv...");
> }
>
> extern(C)
> void send()
> {
>     writeln("send...");
> }
>
>
> int main(string[] argv)
> {
>     //copy from std.socket unittest
>
>     immutable ubyte[] data = [1, 2, 3, 4];
>     auto pair = socketPair();
>     scope(exit) foreach (s; pair) s.close();
>
>     pair[0].send(data);
>
>     auto buf = new ubyte[data.length];
>     pair[1].receive(buf);
>     assert(buf == data);
>
>     return 0;
> }
> ----------------------------------
> send...
> recv...
> core.exception.AssertError at a.d(27): Assertion failure
> ----------------
> ./a() [0x43d61f]
> ./a(_Dmain+0xcc) [0x43d1bc]
> ./a(_D2rt6dmain211_d_run_mainUiPPaPUAAaZiZ6runAllMFZ9__lambda1MFZv+0x1f) [0x4400fb]
> ./a(void rt.dmain2._d_run_main(int, char**, extern (C) int 
> function(char[][])*).tryExec(scope void delegate())+0x2a) 
> [0x44004e]
> ./a(void rt.dmain2._d_run_main(int, char**, extern (C) int 
> function(char[][])*).runAll()+0x30) [0x4400b4]
> ./a(void rt.dmain2._d_run_main(int, char**, extern (C) int 
> function(char[][])*).tryExec(scope void delegate())+0x2a) 
> [0x44004e]
> ./a(_d_run_main+0x1dc) [0x43ffc8]
> ./a(main+0x17) [0x43d637]
> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf5) 
> [0x7f5fabd8fec5]

You basically "overwrite" the C send(2) and recv(2) functions 
with your code (the actual symbols, the linker will yours instead 
the "real" ones). So std.socket doesn't call the C functions but 
yours. Yours obviously don't send and receive data. If you really 
want to "overwrite" these functions you might be able to call the 
original ones via dlsym.